ELSEVIER 0890-6238(95)02015-2

Reproductive Toxicology, Vol. 10, No. 1, pp. 29-36, 1996 Copyright 0 1996 Elsevier Science Inc. Pked in the USA. All rights reserved

OEJO-6238/96 $15.00 + .oO

TWELVE-MONTH EVALUATION OF RHESUS MONKEY DAMS AND INFANTS AFTER RELAXIN (HRLX-2) INFUSION IN LATE PREGNANCY

MARI S. GOLUB,* NORMA J. GALIHER,~ PETER K. WORKING,? and ADAM GREENSPAN~ Departments of *Internal Medicine and SRadiology, University of California, Davis, Davis, CA

TGenentech, Inc., South San Francisco, CA

Abstract -Pregnant rhesus monkeys received daily i.v. infusions of chemically synthesized human relaxin (hRlx-2) (0.1 mg/kg/day N = 6,2.0 mg/kg/day N = 6, vehicle control N = 7) from the onset of cervical softening to delivery (0 to 14 infusions) to simulate potential therapeutic use of this agent for cervical ripening. Repro- ductive fitness of dams was evaluated during the next breeding season, and infants were studied through 12 months of age. Birth weight and size, neonatal heart rate and body temperature and neurobehavioral status were not intluenced by intrauterine relaxin exposure. Neonatal muscle tone was greater and responsiveness was lower in the hRlx-2 treated infants than in controls. No group differences were seen in infant postnatal growth, maturation or incidence of health problems. Maternal endpoints including uterine involution, resumption of menses, conception rate, and pregnancy outcome were similar across groups. Systemic exposure of rhesus monkeys to relatively high levels of hRLx-2 in late pregnancy did not have apparent long term effects for the measures evaluated under conditions of the experiment. Conclusions concerning adverse effects are limited by the small sample size.

Key Words: relaxin; pregnancy; neonate; infant; monkeys; toxicology; development; fertility; growth.

INTRODUCTION

Relaxin is a peptide hormone with a limited distribution of receptor populations located primarily in the uterine myometrium, the uterine cervix and the pubic symphy-

sis. These receptor systems have been shown to promote

uterine quiescence and cervical softening in rats and pigs (1). Systemic relaxin titers do not increase in late preg-

nancy in women (2) or monkeys (3), but local (autocrine/ paracrine) release of relaxin is thought to play a role in labor readiness (4). These properties have suggested the

therapeutic use of exogenous relaxin in late pregnancy for cervical ripening. Human relaxin (hRLx-2) has been

chemically synthesized (5), and clinical trials have been

undertaken in pregnant women (6). Currently, information is rapidly expanding on the

sources, target tissues and physiologic functions of re- laxin (5). Relaxin is also produced in the nonpregnant

Current address for Norma 3. Galiher: Consultant in Toxicology, 434 Carmelita Drive, Mountain View, CA 94040-32559.

Current address for Peter K. Working: Liposome Technology, Inc, 1050 Hamilton Court, Menlo Park, CA 94025.

Portions of this paper were presented at the 1991 Meeting of the Society of Toxicology. Supported by Cienentech, Inc.

Address correspondence to: Mari S. Golub, California Regional Primate Research Center, University of California, Davis, Davis, CA 95616, phone (916)752_5119;FAX (916) 752-2880, email msgolub@ucdavis.edu.

Received 17 April 1995; Revision received 17 July 1995; Accepted 27 July 1995.

29

state and in early pregnancy, and relaxin receptors have

been identified in rat brain (7) and heart (8). Relaxin may

play a role in establishing the uteroplacental vasculature

in early pregnancy (9) and in blood pressure regulation in

the nonpregnant state (10). Exogenous relaxin adminis-

tration is not known to have long term effects on the

reproductive system or on fetal development. However,

no direct examination of reproductive and developmental

toxicity of relaxin is available in the published literature.

The rhesus monkey is a valuable model for human

reproductive toxicity because of the similarity in hor-

monal control of breeding and pregnancy, single off-

spring gestation, and prolonged intrauterine fetal devel-

opment. The rhesus monkey relaxin gene has been

sequenced and homology with the human H2 relaxin gene established (11). Human relaxin is biologically ac- tive in rhesus monkeys (12,13). Earlier studies have

demonstrated that hRlx-2 has a half life of 150 min (14) and reaches the fetus (15) when administered during late pregnancy to the rhesus monkey. In this study, daily infusions of pharmacologic concentrations of hRLx-2

were administered to pregnant monkeys beginning at de- tection of cervical softening and continuing until deliv-

ery. Although this led to a varying number of infusions within treatment groups, it simulated the potential human use of this agent and ensured that the fetus was exposed within 24 h of delivery. It was important to determine whether relaxin would influence neonatal status

30 Reproductive Toxicology Volume IO. Number I. 1996

due to either an indirect action via effects on labor and

delivery or a direct action on the fetus. A broad based evaluation of dam and infant was conducted over the

year following delivery to determine whether infant de-

velopment or dams’ reproductive performance might be adversely influenced by the hRlx-2 infusions.

MATERIALS AND METHODS

Design

Dams were assigned to a treatment group on day

150 gestation with a randomization process designed to balance sex of fetus (as determined by ultrasound).

Original group sizes were N = 7, 6, and 6 (control, 0.1

mg/kg, and 2.0 mg/kg groups respectively). Infant fol- low-up group sizes were 7, 6 and 4; one fetus from the

hRlx-2 2.0 mg/kg group was stillborn and another was

released from the project because of congenital defects

(see Outcome of hRlx-2 treated pregnancy). Dam fol- lowup group sizes were 7, 6, and 6. One dam (0.1 mg/kg

group) was released from the project with a diagnosis of chronic colitis at the end of the followup breeding season

but all data to that point were included in the analysis.

The experiment was conducted blind to treatment group;

the material was coded for administration, and project records contained no indication of treatment until statis-

tical analysis was performed.

Selection of breeders

Multiparous rhesus monkey (Macaca mulatta) dams without a history of reproductive problems were selected from the breeding colony at the California Regional Pri-

mate Research Center (CRPRC).

Animal maintenance

Animal care followed the guidelines of the Federal

Animal Welfare Act and the Institute of Laboratory Ani- mal Resources of the National Research Council (16). CRPRC is accredited by the American Association for

Accreditation of Laboratory Animal Care. Protocols were approved prior to implementation by the University of California Davis Animal Use and Care Administrative Advisory Committee.

Breeders were housed in temperature (60” to 80°F) and photoperiod (lights off 4 PM to 4 AM) controlled

animal rooms in individual stainless steel cages. Cages

and drop pans were cleaned daily, and sterilized clean cages were provided monthly. Animals received a daily visual health check that included vaginal bleeding. Cages of near-term animals were checked daily between 6 and 8 AM for newborns. Any veterinary diagnoses and treat- ments were recorded in the animal’s permanent health record using standard nomenclature.

Dams were adapted to chair restraint and to the procedures required for hRlx-2 administration beginning on day 90 gestation (17). On day 143 +- 3 of gestation an indwelling femoral catheter with a subcutaneous port

was placed under general anesthesia and subsequently

monitored daily for patency. Beginning on day 150 of gestation, dams were examined daily to obtain a Bishop

score, an index of labor readiness based on results of manual vaginal palpation developed for use in human

obstetrics and adapted for monkeys (18). This examina- tion could be conducted without anesthesia after exten- sive adaptation of the animal and involved scoring of

cervical softness, length, dilation, and position and fetal head engagement. Sterile gloves and betadine swabbing of the perineum were used to guard against infection. When the Bishop score indicated labor readiness or when

term (165 days gestation) was reached, dams began to

receive hRlx-2 infusions which continued daily until de- livery. The number of infusions received for individual animals were: control group, 16, 13, 8, 7, 5, 1, 0; 0.1 mg/kg hRlx-2 group, 12, 11, 8, 5, 3, 2, 2; 2.0 mg/kg hRlx-2 group, 14, 14, 12, 8, 5, 3.

infant followup endpoints

Infants were housed from birth in the Primate Nurs- Neonatal period. A physical examination conducted ery, initially in incubators for thermal support and later in by veterinarians on the day of birth included 9 organ

small stainless steel cages. Incubators were supplied with

a terry cloth platform to which the infant could cling while nursing from a bottle. Beginning at 2 to 5 weeks of

age, peer socialization was initiated by housing infants in

groups of 2 or 3 for increasing periods of time until 24-h group housing was achieved.

At 4 to 6 months of age, infants were moved from the nursery to outdoor group housing with other like-

aged peers assigned to the study. The outdoor caging had

chain link walls, a solid roof, supplemental heating and

cooling and perches at a variety of heights.

Infants were fed formula (Enfamil with Iron) during the first weeks of life and gradually weaned to monkey

chow. Older infants and breeders were fed Purina 15

Monkey Chow (Ralston-Purina). Water was available ad libitum via an automatic system.

Drug preparation and administration

hRlx-2 is a form of human relaxin that has two chains of 24 and 33 amino acids and is thought to be the

mature product of the human relaxin gene H2. Chemi-

cally synthesized hRlx-2 and vehicle were obtained from Genentech, Inc. as a 1.67 or 2.0 mg/mL solution

and diluted in sterile saline to a constant volume of 25 ml for each 60 min infusion. hRlx-2 doses of 0, 0.1, and 2.0

mg/kg were based on the dam’s weight on day 150 of gestation. These doses represented the expected clinically

effective dose in humans and a 20-fold greater dose.

Relaxin in rhesus monkeys 0 M. S. GOLUB ET AL. 31

systems (integument, oral cavity, eyes, musculoskeletal, platelets, plasma protein, plasma color, fibrinogen, white

circulatory, spleen/lymph nodes, respiratory, digestive, blood cells, metamyelocytes, band neurtrophils, seg-

urogenital). Body measurements (crown-rump, skin- mented neutrophils, lymphocytes, monocytes, eosino-

folds, head circumference) were obtained at birth, day 7, phils, basophils, nucleated red blood cells, and erythro-

and day 14 postnatal. cyte morphology.

Neonatal neurobehavioral tests (reflexes, muscle

tone, irritability) (19) were administered on days 1 to 5,

7, and 14. The muscle tone evaluation was adapted from

a commonly used human neonatal scoring system, the Amiel-Tison Neonatal Adaptive Capacity Score, and in-

volved rating (none, low, medium, high, scored 0, 1,2, or

3) of resistance to displacement at the toes, fingers, knees, elbows, shoulders, and hips as well as resistance

of the head to dorsiflexion and response of the wrist and

ankle to dorsiflexion. Scores were totalled over all sites

to give an overall index of muscle tonus. Physiologic

stability was evaluated from continuous recording of

heart rate and core temperature obtained with a Hewlett-

Packard Neonatal Monitor during a l-h period on the

first day of life. In addition, overnight videotapes were

made on the first night after birth, and two subsequent nights during the first 4 d postnatal for evaluation of

sleep cycles. Spontaneous behavior was observed and scored for motor and postural maturity during a lo-min period on days 3 and 14 postnatal.

Dam follow-up endpoints

Postpartum period. A veterinary exam on the day of birth included uterine involution, placental retention,

vaginal inspection for lacerations, contusions and other

signs of dystocia, and a general evaluation of organ sys-

tems (integument, oral cavity, eyes, musculoskeletal, cir-

culatory, spleen/lymph nodes, respiratory, digestive, uro-

genital). Uterine involution was followed by ultrasound

at 2 to 3 day intervals until complete. Blood samples for

determination of relaxin antibodies were obtained at 3,6,

and 12 weeks and 6, 9, and 12 months postpartum.

Relaxin antibody assays. Neutralizing antibodies

were detected (+ or -) in a bioassay as a lower (>2 s.d.

below values obtained from control dams) level of CAMP generated by cultured human uterine cells when human relaxin (TN285, Genentech, Inc.) preincubated

with serum samples was added to the culture.

Growth and maturation. Infant developmental ex-

ams at 1, 3, 5, 7, 9, and 12 months of age included growth parameters (weight, crown rump length, head cir-

cumference, arm and thigh circumference, skinfold thickness, femur length) and maturational parameters

(tooth eruption, skeletal maturation as determined from

radiographs, anogenital distance) and a complete physi-

cal exam by organ system. Radiographs of both limbs (including hands/feet, elbows/knees, wrists/ankles and end of long bones) were taken at each exam and were

evaluated for age-appropriate maturational landmarks by the consulting radiologist (AG) according to previous studies in this laboratory (20) and information in the literature (21).

Health surveillance. All instances of veterinary di-

agnoses and treatment were identified in the individual medical record for each animal. Common disorders were

divided into general categories (gastrointestinal, skin rash, dehydration, trauma) for summary. Blood samples were obtained at each developmental exam (1, 3, 5, 7, 9, 12 months) for hematology and clinical chemistry. The

30 endpoints measured at each timepoint were serum chloride, carbon dioxide, potassium, sodium, anion gap, albumin, blood urea nitrogen, glucose, total protein, liver enzymes (SGPT, GGT), alkaline phosphatase, calcium, creatinine, phosphorous, red blood cells, hemoglobin, he- matocrit, mean corpuscular volume, mean corpuscular he- moglobin concentration, mean corpuscular hemoglobin,

Menstrual cycle and breeding. Resumption of men-

ses after delivery was monitored daily and entered into a

computerized cycle record. Timed mated breedings were scheduled and recorded weekly. Females were mated

with proven male breeders two times each month on

alternate days around the estimated time of ovulation (as

determined from menstrual cycle records) using stan-

dardized breeding colony procedures. Mating was de- tected from vaginal smears and pregnancy was verified

by ultrasonography on day 30 of gestation. Fetal growth and viability were evaluated by ultrasound on day 90 and 120 of gestation. Hematology and clinical chemistry

were determined at 3 month intervals until conception and at 45 d intervals during pregnancy (for measures, see

Infant Followup Endpoints: Health Surveillance). Dur-

ing pregnancy, body weights were determined at monthly intervals from the estimated date of conception.

Outcome of the follow-up pregnancy. A physical exam was conducted on dam and neonate on the day of

birth as described above (Outcome of hRlx-2-treated

pregnancy). Neonatal physical, morphometric, and neu- robehavioral exams were conducted on the day of birth as described above.

Statistical analysis All statistical analyses were conducted with Statis-

tical Analysis System (SAS) programs. Both parametric and nonparametric statistics were used depending on dis- tribution characteristics of parameters. The most com-

32 Reproductive Toxicology Volume 10. Number 1, 1996

mon approach taken was a one factor (treatment group)

analysis of variance (ANOVA) with post-hoc Bonferroni

r-tests. Post-hoc Dunnett’s tests were sometimes used for

behavioral measures. The body muscle tone score from

the neonatal neurobehavioral test battery was analyzed with the Mann-Whitney U-test. Measures evaluated in a

serial manner were analyzed with repeated measures pro-

cedures. Statistical tests indicating group differences at P

< .05 were considered significant. For post-hoc tests, the

probability required to reach statistical significance was

corrected for the number of comparisons made. For the

30 measures obtained from hematology and clinical

chemistry reports, ANOVAs with Bonferroni post-hoc

tests were conducted at each timepoint for each param-

eter. Statistically significant ANOVAs were considered

potentially relevant to treatment if both treated groups

deviated in the same direction from controls and if the

post-hoc test was significant for both treated groups or for the high dose (2.0 mg/kg hRlx-2) group. Group

means for potentially relevant comparisons were com- pared to informal normative data for adult rhesus avail-

abie at CRPRC.

RESULTS

Outcome of the hRlx-2 treated pregnancy

Eighteen of the 19 pregnancies ended in term, live

vaginal births (Table 1). One infant in the 2.0 mg/kg

group was stillborn; diagnosis at necropsy indicated sep- ticemia associated with positive Staphylococcus sp.

cultures. One newborn (2.0 mg/kg group) was released from

the project when congenital abnormalities (macrofossus

and pectum excavatum) were identified at the birth exam. The nature of these abnormalities indicated an

origin prior to hRlx-2 treatment, which did not begin until late third trimester. No treatment related abnormali-

ties were noted in the dams’ postpartum exams. An ob-

servation of mammary gland thickening and enlarged

Table 1. Outcome of hRlx-2-treated pregnancies

Treatment group

Controi 0.1 mgIkg

hRix-2 2.0 mgikg

hRlx-2

Number of dams 7 6 6 Age bears) Initial weight (kg) parity Number of infusions Gestation length (days) Live, vaginal births Birth weights (g)

10.0 2 3.3 7.7 + 1.9 7.0 + 0.9” 7.8 -t 1 .O 6.6 + 0.7 7.1 f 0.8 X922.1 2.3k2.1 I.8 + 1.2

726 6*4 9*5 16425 163+5 164+5

7 6 FP 464241 446r24 414 r 24

Values are mean f SD. “Significantly different from controls, P 4 0.05. bOne infant stillborn.

mammary lymph node was made in one dam in the 2.0

mg/kg hRlx-2 group, but no normative data are available to indicate whether this was treatment related.

Infant followup

Neonatal period. Neonatal growth, physical exams,

morphometric parameters, physiologic parameters, and

clinical pathology endpoints were within normal ranges

and no group differences were indicated. In neurobehav-

ioral tests, muscle tonus was greater in the 0.1 hRlx-2

treated group on the day of birth, but groups were

equivalent by day 2 postnatal (Table 2). There was a

significant effect of treatment on responses to 10 re-

peated heel pinpricks recorded in the hRlx-2 treated in-

fants on the third (F = 5.52, p = .017) and fourth (F = 5.43, p = .019) day of life. There were no group differ-

ences in stability of heart rate or core temperature mea- sured on the first day of life. Scores varied widely across

animals for overnight rest-activity patterns, level of ac- tivity, and maturity of observed behaviors, and statistical

analysis did not reveal any group differences.

Growth and maturation through 12 months of age.

Morphometric measures reflected several dimensions of

growth including weight gain (body weight), subcutane-

ous fat deposition (skinfold thickness), linear growth

(crown-rump length), and development of lean body mass (arm and thigh circumference). No group differ-

ences were found for any growth parameter at any age

(Table 3). No signs of abnormal bone maturation were de-

tected in the radiographs of long bone epiphyseal growth centers and wrist/ankle bones taken at each examination.

Expected landmarks were seen at each age and no signs of excess mineralization associated with compensatory

growth (which would indicate a growth lag between ex- ams) were indicated. There were no statistical group dif-

ferences in the number of teeth erupted at each age ex- amined. All animals had a full set of 20 primary teeth by

7 months of age. For anogenital distance, the expected effect of sex was found but there were no treatment or

treatment-by-sex effects at any age.

Clinical pathology and health problems though 12 months of age. Clinical parameters at the first two time-

points (1 and 3 months of age) reflected variability typi- cal of infancy. Four statistical effects were detected by the 60 ANOVAs conducted at this time but no treatment or pathology related pattern was evident (TabIe 4). He- matology and clinical chemistry parameters were similar across treatment groups at the later test dates (5 to 12 months of age). Two incidences of statistical group dif- ferences in 120 ANOVAS conducted during this time period were not dose related, were not associated with

Relaxin in rhesus monkeys 0 M. S. GOLUB ET AL.

Table 2. Neonatal neurobehavioral parameters from hRlx-2-exposed infants

33

Days postpartum

0 1 2 3 4

Muscle tone (total score, max 60) control 0.1 mg!kg hRlx-2 2.0 mg/kg hRlx-2

Response to pinprick (number, max 10) control 0.1 mg/kg hRlx-2 2.0 m&g hRlx-2

54 + 5” 54*4 6Oi5 55 * 5 58 f 7 59 f 5b 56*6 51*6 6020 60* 10 56 + 2 59 + 6 6Oi4 57 + 10 60+2

7 f 4c 6+5 6+4 I*3 9&l 3+3 2+2 4+3 2 + 3d 5&ld 5*5 5+6 4+5 4+4 4+2

Fourteen parameters from the neurobehavioral test battery were analyzed. Significant group differences were noted only for the two parameters presented (see text). “Median f interquartile range. bControl vs. 0.1 mg/kg hRlx-2, U = 5.5, P = 0.025. “Mean f SD. dSignificantly different from control, Bonferroni post hoc test.

changes in other parameters, and were considered unre-

lated to treatment. No major pathologic conditions were recorded for

any animal. There were no treatment group differences in

the type or frequency of occurrence of minor health problems. One infant (control group) was released from

the study at 4 months of age because of a consistent record of poor health and growth and failure to respond

adequately to socialization. Despite continuous individu- alized care in the nursery, experience with this animal indicated that it would not survive in outdoor social

housing. Data recorded for this animal up to the time of release are included in the statistical analysis.

Maternal followup

Relaxin and relaxin antibodies. Relaxin antibodies

were detected at 3, 6, and 12 weeks postpartum in 216

dams in the 0.1 mg/kg group and 3/6 dams in the 2.0

mg/kg group (Table 5). One additional dam in each

group had relaxin antibodies at 3 and 6 but not 12 weeks.

Not all animals were sampled from 9 to 15 months post- partum because sampling was discontinued during preg-

nancy. Two of 4 hRlx-2 treated dams sampled also had

positive antibody tests at 9 months postpartum and 1 of 2 sampled at 12 months also had a positive test. In ad-

dition, one positive test near threshold value was re- corded for each of 3 control animals (Table 5).

Dams’ hematology, clinical chemistry, and physical

exams. No animals were pregnant at the 3-month time

point. However at 6 and 9 months, some animals had

become pregnant, and data were thus analyzed both in- cluding and excluding the pregnant animals. No consis-

tent hematology or clinical chemistry group differences

Table 3. Growth of rhesus monkey infants exposed to hRlx-2 in late gestation

Treatment group

Control 0.1 mg/kg hRlx-2 (n = 6) (n = 6)

2.0 m&g hRlx-2 (n = 4)

Body weight (g)

Crown rump (cm)

Head circumference (cm)

1 month 675 + 113 674 + 103 671 i 109 3 months 1004 + 132 1053 + 228 991 f 106 5 months 1297 + 117 1293 + 249 1134i89 I months 1573 f 210 16302301 172lklll 9 months 1886*268 1933 + 343 2032 + 119

12 months 2218 + 333 2220+452 2210 i 92 1 month 21.3 zt 1.2 21.5 + 1.4 21.4 zt 1.6 3 months 25.8 + 1.2 24.9 + 1.8 24.8 + 1.4 5 months 28.4 + 2.0 28.0 ? 1.6 28.0 f 1.2 7 months 30.3 * 1.3 30.4 & 2.1 30.5 f 1.1 9 months 32.6 k 1.9 32.5 + 2.1 33.3 f 1.0

12 months 35.5 f 1.3 35.0 + 1.7 35.1 + 0.7 1 month 21.2 + 0.7 21.4 f 0.8 22.0 f 0.7 3 months 22.1 f 0.7 22.3 + 1.2 22.8 f 0.6 5 months 23.3 zt 0.8 23.7 + 1.1 23.3 + 0.4 7 months 24.1 + 0.6 24.5 + 0.9 24.6 f 0.4 9 months 24.8 f 0.7 24.8 f 1.2 25.0 f 0.5

12 months 25.2 f 0.8 25.3 + 1.0 25.2 + 0.5

There were no indicated group difference at any age for any parameter. Other measures taken (arm and thigh circumference, skinfold thickness) also showed no group differences. Values are means f SD.

34 Reproductive Toxicology Volume IO. Number I. 1996

Table 4. Results of potentially treatment-related ANOVAs of hematology and clinical chemistry end points

0.1 m&g 2.0 mg/kg Time point Parameter ANOVA Control hRlx-2 hRlx-2

Dams 6 months postpartum Plasma protein (g/dL) F(2,15) = 6.22. P = 0.011 7.2 2 0. I 7.8*0.1i’ 7.8 + 0.2 6 months postpartum Monocytes (%) F(2,lS) = 6.08, P = 0.012 4t 1 I f 0.3” 2 * 0.3;’

Infants hRlx-2 treated pregnancy 1 month of age Blood urea nitrogen (mg/dL) H2.13) = 6.92, P = 0.009 12*2 6+ I 4* I”

Infants Follow-up pregnancy day of birth Alkaline phosphataae (U/I*) H2.9) = 5.05. P = 0.034 286 + 66 419261 5 IO f 35”

The time points for dams were 3 and 6 months postpartum (after the hRlx-2-treated pregnancy) and 4.5, 90, and 135 days gestation and day of birth (follow-up pregnancy). The time points for hRlx-2 treated infants were birth, 1, 3, 5.7.9, and 12 months of age. Infants from the follow-up pregnancy were evaluated only on the day of birth. For a list of measures obtained at each timepoint see text (lnj&zt folllow-up end poinrst health surveifiance). Values are mean f SEM. “Treatment groups significantly different from controls, Bonferroni post hoc test.

were observed; expected postpartum and pregnancy re-

lated changes were noted in all dams. Scattered statisti-

cally significant treatment group differences from con- trol were seen for some parameters at some endpoints,

but no treatment- or pathology-related pattern was noted. In three ANOVAS (total protein, plasma protein, and

monocyte counts six months after the hRlx-2 treated pregnancy) both treated groups differed from controls

(Table 4). There were no group differences in incidence of

health problems. A general pattern of poor health, in- cluding liquid stool, poor appetite, and dehydration, was

apparent in one dam (0.1 mg/kg group) who was subse-

quently released after a colon biopsy diagnosis of chronic colitis. Records indicate that 27.2% of animals

dying at >4 yrs of age in the colony from 1988 to 199 1 had similar alimentary tract lesions. No abnormalities

were observed during the general physical exams. One animal in the 0.1 mg/kg hRlx-2 group exhibited en-

larged/dilated uterine vessels during an ultrasound exam

for pregnancy detection.

Breeding outcome. The conception rate for the ex-

periment as a whole was 74% as compared to a colony wide value of 69.4% during that same breeding season.

There were no treatment group differences in the number

of conceptions, the mean number of breedings to con- ception, or time to conception (Table 6). There was no

relationship between breeding success and presence of relaxin antibody titers across animals.

Follow-up pregnancy parameters. The 0.1 mg/kg

group had lower average weight prior to pregnancy and a greater average weight gain during pregnancy (1.25 f 0.18 vs 1.04 + 0.08 kg, mean + sem) than the control group. No treatment-related effects on fetal intrauterine growth were detected from measures obtained during maternal ultrasound exams.

Follow-up pregnancy outcome. Ten of the 14 preg- nancies ended in normal term (155 to 170 days) live vaginal births. One dam (2.0 mg/kg group) aborted at 39

days gestation, one fetus (control) was stillborn, one dam

(control) delivered postdates (174 days gestation), and

one postdates pregnancy (2.0 mg/kg group) was termi- nated by cesarean section at 176 days. Background data

from CRPRC during the same breeding season indicated that 14.3% of pregnant rhesus monkeys had spontaneous

abortions and 12% of deliveries were postdates (>170

days). There were no group differences in mean birth

weights (control, 0.516 + 0.07 kg; 0.1 mg/kg hRlx-2, 0.494 f 0.02 kg; 2.0 mg/kg hRlx-2, 0.490 + 0.09 kg,

mean + sd) or morphometric measures of newborns. In

neurobehavioral testing, the 2.0 mg/kg hRlx-2 group had significantly lower body tonus than controls (U = 0, P

= .012). There were no other group differences in neu- robehavioral parameters. All dams and infants were re-

ported to be in “excellent” or “good” overall condition at the postpartum exam. Eye bruising, indicative of a

difficult labor was reported in 1 infant in the 0. I mg/kg group. One neonate (2.0 mg/kg group) was judged slight-

of-frame and also had the lowest birthweight in the study (420 g). Potentially treatment related ANOVAs were sta- tistically significant for alkaline phosphatase (Table 4).

DISCUSSION

There are both advantages and disadvantages to use of data from this experiment in evaluating health risk of late pregnancy relaxin administration. In the rhesus

Table 5. Detection of relaxin antibody in dams after hRlx-2 administration in late pregnancy

Treatment group

Time postpartum Control 0.1 mg/kg hRlx-2 2.0 mg/kg hRlx-2

3 weeks on 216 316 6 weeks o/7 216 316

I2 weeks o/7 116 216 9 months 216 l/4 214

12 months l/6 214 If2 IS months O/l O/l o/o

Ratios are the number of positive assays/number of dams assessed.

Relaxin in rhesus monkeys 0 M. S. GOLUB ET AL. 35

Table 6. Menstrual cycle and breeding evaluations by group

Control (excipient) 0.1 mg/kg hRlx-2 2.0 mg/kg hRlx-2

First sign of menses (days postpartum) Animals conceiving Breedings to conception Time to conception (days postpartum)

Values are mean + SEM.

89 + 62 511

2.6 + 1.7 236+41

monkey model it is possible to conduct clinical evalua-

tions directly comparable to those used in humans. Be-

cause of the ability to use high doses, precise control of

dosing and environments and the feasibility of long term

follow-up, the animal model is more sensitive than the human obstetric situation. However, small sample sizes

would not allow statistical detection of low incidence

adverse effects. Further, statistical power is limited for

continuous variables.

Doses used in this study included a pharmacologic level (0.1 mg/kg) for intravenous use and a dose 20 times the pharmacologic level (2.0 mg/kg). Relaxin use in

clinical trials has been limited to vaginal application.

Although serum hRlx-2 levels are not available from the

present study, previous investigations in the pregnant

rhesus monkey have shown that peak serum levels dur-

ing a one-hour infusion of 2.0 mg/kg hRlx-2 were 1500 ng/mL or approximately lo4 greater than preinfusion lev-

els (15). In contrast, vaginal application of hRlx-2 during clinical trials in pregnant women did not elevate circu-

lating relaxin concentrations (6). Thus, although mini- mally toxic doses were not identified, the high dose used

here can be considered to represent a substantial margin of safety for therapeutic uses.

There has been some concern that the onset of labor might be prevented or delayed in relaxin-treated preg- nancies due to reduction in uterine contractility. No in-

dication of prolonged gestation or labor dystocia was

seen in the hRlx-2 treated pregnancies. Similarly, no de-

lay in delivery was noted in a previous study when re- laxin infusions were conducted between 142 and 148

days gestation in monkeys (22). Similarly, no effects on

pregnancy outcome are associated with high circulating levels of relaxin in late gestation in diabetic women (23)

and elevated circulating relaxin levels are not associated with preterm labor in obstetric patients (24). There is some evidence from in vitro studies that the human myo- metrium is not as sensitive to antagonism by relaxin

as that of pigs (25) but no information is available for monkeys.

Research on cardiovascular effects of relaxin (10) suggest a possible impact on maternal, fetal and neonatal cardiovascular parameters. In a previous study (22), no fall in maternal blood pressure was noted during infu- sions at the 0.1 and 2.0 mgkg doses and fetal heart rate

104+50 14 + 34 316 616

3.0 f 2.6 1.8kO.7 232 + 70 175 + 36

patterns (as determined by Doppler ultrasound) did not

show abnormalities. Further, a one-hour monitoring of

neonatal EKG on the day of birth did not detect qualita-

tive or quantitative treatment effects. Locally produced

endogenous relaxin may be involved in regulation of

blood pressure, but no signs of cardiovascular toxicity

were apparent as a result of infusion of exogenous

relaxin. Exposure to relaxin clearly led to long term pres-

ence of relaxin antibodies in the dams’ circulation; 2/6

dams in the 0.1 mg/kg group and 3/6 dams in the 2.0

mg/kg group had antibodies 12 weeks after the last hRlx-2 administration. We were not able to follow dams

long enough to determine if and when antibody titers

disappeared. Also, it is noteworthy that occasional posi-

tive tests near the detection limit were recorded in con-

trols. However, presence of antibody did not apparently

influence subsequent conception. All dams in the 2.0

mg/kg group conceived and 516 animals carried the preg- nancy to term; there was one abortion and one postdates

pregnancy in the 2.0 mg/kg group. In the control group, there was one stillborn and one postdates pregnancy. No

statistical conclusions can be drawn from this small num-

ber of pregnancies, but considering the high dose admin- istered, and colony statistics, no pattern of concern is

indicated. Also, no effects on pregnancy outcome were

identified in an earlier study in which hRlx-2 was ad- ministered to rhesus monkeys in late gestation but prior

to labor readiness (22). Nonetheless, a full multigene-

ration study in rodent species would be helpful in evaluating effects of relaxin and relaxin antibodies on reproduction.

In rats, relaxin antibodies have been shown to in- terfere with nipple development and pup survival (26).

Nipple morphology could not be evaluated in detail from external examinations conducted in this study, and, be- cause our hRlx-2 treated infants were raised in the nurs-

ery, we did not have an opportunity to evaluate lactation.

Studies in humans indicate that the fetus does not produce relaxin and is apparently not exposed to detect- able levels of maternally produced endogenous relaxin (27). However, fetal serum concentrations are about 1% of maternal concentrations when exogenous HRlx-2 is administered to the pregnant rhesus monkey (15). No known receptors for relaxin exist in the fetus, although

36 Reproductive Toxicology

receptors in heart and brain have been demonstrated in the early postnatal period in the rat (28). The only sug-

gested fetal effects in the current study were transient

group differences from control in muscle tone in both the

hRlx-2 treated pregnancy and the followup pregnancy.

These effects did not indicate a pattern of pathology and

were similar in type and extent to those observed after

administration of obstetric analgesics (29).

Since relaxin belongs to the family of peptide hor-

mones that includes insulin and insulin-like growth fac-

tors (5) and has been demonstrated to stimulate GH se-

cretion in nonpregnant monkeys (12), it was important to

evaluate growth. Although the sample sizes used here would not be sensitive to small differences in size or

growth rate, no indication of group differences was seen,

even at the high intravenous dose. All infants from the

hRlx-2 treated pregnancies were within colony birth-

weight norms. In conclusion, a broad based evaluation after late

pregnancy hRlx-2 treatment of rhesus monkeys did not

provide any suggestion of pathology or abnormality in

growth and health of infants or subsequent breeding ca-

pability of dams.

Acknowledgments - All technical aspects of the study were conducted by Kelly A. Weaver and Dorene P. Bishop. This study was supported by Genentech Inc., South San Francisco, California, and was conducted under Good Laboratory Practice regulations with the assistance of the Quality Assurance Unit at CRPRC.

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