Relationships between concentrations of ovarian steroids, insulin-like growth factor-1 and...

EISEVIER

ANIMAL REPRODUCTION

SCIENCE Animal Reproduction Science 41 (1996) 119- 129

Relationships between concentrations of ovarian steroids, insulin-like growth factor- 1 and

IGF-binding proteins during follicular development in the ewe

M. Khalid, W. Haresign *

Faculty of Agricultural and Food Sciences, Uniuersily of Nottingham, Sutton Bonington Campus, Loughborough, LE12 5RD, UK

Accepted 18 August 1995

Abstract

The objective of the present study was to determine how insulin-like growth factor-l (IGF-1) and IGF-binding proteins (IGFBPs) are related to in vivo follicular development in the sheep. Oestrus was synchronised in 20 cyclic ewes and the animals were slaughtered 44 h after the second injection, just before the start of preovulatory luteinising hormone (LH) surge. Normal growing follicles were dissected from the ovaries of each ewe and their diameters measured. The follicular fluid was aspirated and assayed for oestradiol, testosterone and total IGF- 1 content. The follicles were classified as either non-oestrogenic or oestrogenic if the follicular fluid content of oestradiol was less than 60 ngml- ’ or more than 60 ng ml-‘, respectively. The mean diameter of oestrogenic follicles was significantly (P < 0.001) higher than that of non-oestrogenic ones, but testosterone concentrations did not differ. IGF-1 concentrations in oestrogenic follicles were significantly (P < 0.01) lower than those in non-oestrogenic ones, with a significant (P < 0.01) negative correlation between follicular oestradiol content and IGF-1 concentration. IGFBPs were

identified by Western ligand blot analysis using 12% sodium dodecyl sulphate polyacrylamide gel electrophoresis under non-reducing conditions and band intensities on autoradiographs were quantified by scanning densitometry. The intensity of the doublet of IGFBP at 44-42 kDa was significantly (P < 0.02) higher in follicular fluid from oestrogenic follicles, whereas the intensity of the band at 35 kDa was significantly (P < 0.001) higher in follicular fluid from non-oestro- genie follicles. Some of the non-oestrogenic follicles also exhibited bands at 32.0-28.5 kDa with

* Corresponding author. Tel.: (01 15) 95 1 6056; fax: (01 15) 95 1 6060; e-mail: [email protected].

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120 M. Khalid, W. Haresign/Animal Reproduction Science 41 (1996) 119-129

variable intensities, but such bands were totally absent in oestrogenic follicles. The results of this study suggest an involvement of both IGF-1 and IGFBPs in ovine follicular development.

Keywords: Sheep-ovary; IGF-1; IGFBPs; Folliculogenesis

1. Introduction

While cell differentiation in ovarian follicles is controlled largely by pituitary gonadotrophins and ovarian steroids (Richards, 1980; Dorington et al., 1983; Amsterdam and Rotmensch, 1987; McNeilly et al., 1991), a number of peptide growth factors have also been implicated in the local regulation of granulosa cell function (Hsueh et al., 1984). Of these, the involvement of insulin-like growth factor-l (IGF-1) in the growth, development and differentiation of ovarian follicles is well documented (see for review Adashi et al., 1985). On the basis of in vitro studies, IGF-1 has been shown to enhance follicle stimulating hormone (FSH) stimulated oestrogen and progesterone production in murine (Adashi et al., 1985; Davoren et al., 1985), bovine &hams, 19871, porcine (Veldhuis et al., 1987; Maruo et al., 1988) and ovine (Monniaux and Pisselet, 1992) granulosa cells. Moreover, relationships have been shown to exist between follicular fluid concentrations of IGF-1 and various biochemical markers of cell differentiation in cattle (Spicer et al., 1988; Echternkamp et al., 1990; Spicer and Enright, 1991) and pigs (Meurer et al., 1991).

In biological fluids, IGFs are bound to specific, high affinity binding proteins (Drop et al., 1991) which can modulate the actions of IGFs within the ovary (Clemmons, 1992). In porcine follicles, the profile of IGF-binding proteins (IGFBPs) depend upon their stage of development (Mondschein et al., 1990). In the ewe, follicular growth and atresia have been reported to be influenced less by changes in IGF-1 concentrations than by changes in IGFBP levels (Monget et al., 1993). However, growth and atresia in that study was determined by microscopic examination of the granulosa cells of individual follicles rather than by biochemical markers of cell differentiation. In the present study, therefore, an attempt has been made to relate changes in IGF-1 and IGFBPs in follicular fluid to physiological status of follicles as determined by steroidogenic content of follicular fluid. Follicles used in this study were collected from cyclic ewes during the follicular phase of their oestrous cycle.

2. Materials and methods

2.1. Animals and management

Twenty cyclic Mule ewes (Blueface Leicester c? X Swaledale Q) were housed indoors under conditions of natural daylength and temperature, and fed a maintenance ration of hay and concentrates, with water always available. Oestrus was synchronised in all ewes by giving two i.m. injections of 100 p,g of a PGF2a analogue (Estrumate;

M. Khalid, W. Haresign/Animul Reproduction Science 41 (1996) 119-129 121

Coopers Animal Health Ltd., Macclesfield, UK) 9 days apart. All ewes were slaughtered 44 h after the second injection, and blood samples collected 38, 41 and 44 h after the second injection were analysed for LH concentrations to confirm that all follicles had been collected prior to the onset of the pre-ovulatory LH surge. Soon after slaughter, all visually normal growing follicles (2 mm diameter or larger) were dissected from each ovary. Any follicle showing visual signs of atresia was rejected. Follicular fluid was aspirated with a 26-gauge needle and divided into two equal portions of at least 30 l.~l. In the case of small follicles, in which the volume of follicular fluid was insufficient to achieve two portions of 30 ~1 each, follicular fluid from the same category of follicles (preferably from the same animal) was pooled. One portion of each follicular fluid sample was stored at - 20°C for the estimation of IGF-1 and IGFBPs; the other portion was diluted with 500 ~1 of Hank’s balanced salt solution (Sigma Diagnostics, St. Louis, MO) before storage at - 20°C and was used to determine the steroid content of individual follicles.

2.2. Oestradiol assay

Measurements of oestradiol concentrations in follicular fluid were carried out without prior extraction by the method validated by Foxcroft et al. (1987). The limit of the sensitivity of the assay within the present study was 15 pgml-‘, samples were analysed in a single assay and the intra-assay coefficient of variation was 7.8%.

2.3. Testosterone assay

The assay used for the measurement of testosterone in follicular fluid was based on the method described by Purvis et al. (1974), but without prior extraction. The method was validated by comparing the values obtained from a range of samples with and without extraction. The correlation coefficient obtained was 0.88 (P < O.OOl>, and samples assayed at different volumes showed parallelism with the standard curve. The limit of sensitivity of the assay within the present study was 0.02 ngml- ‘, all samples were analysed in a single assay and the intra-assay coefficient of variation was 11 .l%.

2.4. IGF-I assay

Immunoreactive IGF-1 in follicular fluid was determined by radioimmunoassay after an acid-ethanol extraction to dissociate IGF-1 from its binding proteins using the method of Daughaday et al. (1980). The antiserum for IGF-1 assay was kindly provided by Dr. S. Spencer (MAF Technology, Ruakura Agricultural Centre, New Zealand). The same highly purified batch of IGF-1 (Peninsula Laboratories, Europe Ltd., St. Helens, UK) was used for both standards and radioiodination. Briefly, aliquots of follicular fluid were diluted 1:4 with a mixture of 87.5% ethanol and 12.5% 2 N HCl and incubated for 30 min at room temperature. The samples were then centrifuged for 30 min at 200C1 X g and 4°C. After neutralisation with 0.855 M Tris, the supematant was then used in the


IGF-1 (np) or Folilllar Fluid @I)

Fig. 1. Demonstration of parallelism between the IGF-1 standard curve (0) and extracted samples of serial dilutions of pooled follicular fluid ( ??1. Binding is expressed as a percentage of the zero value on the standard curve.

radioimmunoassay. This extraction procedure resulted in parallelism between the IGF-1 standard and different volumes of ovine follicular fluid (Fig. 1).

2.5. IGFBP analysis

IGFBPs in follicular fluid were identified by the method described by Hossenlopp et al. (1986). Briefly, 1.0 l.~l of follicular fluid was submitted to 12.0% sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) under non-reducing conditions. The separated proteins were electroblotted onto nitrocellulose filters which were treated with phosphate-buffered saline (PBS; 0.01 M, pH 7.4) containing 0.1% Nonidet P-40, 0.5% gelatin and 0.1% Tween-20, and then incubated overnight at 4°C with 1251-labelled IGF-1 (0.6 X lo6 cpmml-‘) in a sealed plastic bag with 5 ml 0.05 M phosphate buffer at pH 7.4. After incubation, the nitrocellulose membranes were washed three times for 90 min in PBS (pH 7.4) containing 0.1% Tween 20. The membranes were air-dried, and then exposed to Amersham Hyperfilm-MP in a casset with intensify- ing screens for one night at -70°C. Band intensity on autoradiographs of individual follicles was quantified by scanning densitometry.

2.6. Statistical analysis

A bimodal distribution of follicles was observed when frequency was plotted against oestradiol concentrations (Fig. 2). On the basis of this frequency distribution, individual follicles were classified as oestrogenic or non-oestrogenic if they had follicular fluid concentrations of oestradiol of over 60 ng ml- ’ or less than 60 ng ml-‘, respectively. The comparisons of follicle diameter, testosterone, IGF-1 and IGFBP band intensities between oestrogenic and non-oestrogenic follicles were undertaken by analysis of

M. Khlid W. Haresign/Animal Reproduction Science 41 (I 996) 119-129 123

31-60 61-70 71-60 81-110 Ill-140 ,141

Oestradiol Concentrations (@ml)

Fig. 2. Scatter diagram showing frequency distribution of follicles against oestradiol concentrations in the

follicular fluid.

variance, while relationships mined by regression analysis.

3. Results

between follicular fluid steroids and IGF-1 were deter-

A total of 37 oestrogenic potential ovulatory follicles was collected from 20 ewes, giving a ovulation rate of 1.85 f 0.21 follicles per ewe. This is very similar to the ovulation rate recorded for this breed in a range of other studies (M. Khalid and W. Haresign, unpublished observations, 1993).

The data comparing oestrogenic and non-oestrogenic follicles are presented in Table I. The mean diameter of oestrogenic follicles was significantly (P < 0.001) greater than that of non-oestrogenic ones, but testosterone concentrations did not differ. IGF-I

Table I Mean steroid, IGF- I and IGFBP contents in follicular fluid of non-oestrogenic and oestrogenic follicles

Variable Follicle type

Non-oestrogenic Oestrogenic

SEDCSEM) P

No. of follicles I8 37 Diameter (mm) 4.1 5.3 Oestradiol (ngml-’ 1 19.6 121.7 Testosterone (ng ml - ’ ) 0.26 0.38 IGF-I (ngml-‘) 375.0 250.0

ICFBP CC//*/ - ‘I

44-42 kDa 35 kDa

31 kDa

28.5 kDa Total

0.6 1 1.24 0.49 0.17

0.05 0.00 0.05 0.00 1.18 I.41

0.23 < 0.001

7.80 < 0.001

0.12 NS

47.1 < 0.01

0.25 < 0.02 0.08 < 0.001

(0.03)

(0.02) 0.29 NS

124 M. Khalid, W. Hares&n/Animal Reproduction Science 41 (1996) 119-129

kDa Non-oestrogenic Oestrogenic

35 32

28.5

Fig. 3. Western ligand blot analysis of representative examples of IGF-binding proteins in the follicular fluid of three non-oestrogenic and three oestrogenic follicles. Note the differences in the array of binding proteins between the two categories.

concentrations were significantly (P < 0.01) lower in large oestrogenic follicles than in small non-oestrogenic ones. A significant (P < 0.01) negative correlation was observed between follicular fluid oestradiol content and IGF-1 concentrations, although this accounted for only 19% of the variation in IGF-1 concentrations among follicles.

The band intensities of IGFBPs also differed between the two categories of follicles as illustrated in Fig. 3. The mean band intensity of the doublet of IGFBP at 44-42 kDa (presumed BP3) was significantly (P < 0.02) greater in follicular fluid from large oestrogenic follicles, whereas the mean intensity of the band at 35 kDa (presumed BP2) was significantly (P < 0.001) higher in follicular fluid from small non-oestrogenic follicles (Table 1). In addition, some of the non-oestrogenic follicles exhibited additional bands of IGFBP at 31 and 28.5 kDa with variable intensities, but such bands were totally absent in large oestrogenic follicles (Fig. 3). In spite of these differences in the array of IGFBPs between the two follicle classes, the total quantities of BPS were not significantly different (Table 1).

4. Discussion

It should be noted that all follicles were harvested before the onset of the preovulatory LH peak, and therefore at a time when potential ovulatory follicles should be highly oestrogenic. Indeed, the similarity in the mean number of oestrogenic follicles per ewe in this study and the known ovulation rate for this breed would suggest that all follicles classified as oestrogenic were active preovulatory follicles.

The major findings of this study were a negative relationship between IGF-1 concentrations in follicular fluid and oestrogenic status of the follicles, and a difference in IGFBP profile between oestrogenic and non-oestrogenic follicles. Oestradiol concentrations in follicular fluid increased markedly as follicles developed, while intra-follicular IGF-1 concentrations decreased. Potential ovulatory (oestrogenic) follicles therefore

M. Khalid, W. Hares&/Animal Reproducrion Science 41 (1996) 119-129 125

contained significantly lower IGF-1 concentrations compared to non-ovulatory ones. The results of another study from this laboratory have also indicated a significant negative relationship between IGF-1 concentrations and oestrogenic status of follicles, but no such relationship existed between follicular fluid IGF- 1 concentrations and follicular development when only follicle diameter was taken into consideration (Haresign et al., 1994). A similar negative correlation between follicle diameter or oestrogenic status and intrafollicular IGF-1 concentrations has previously been reported for cows (Spicer et al., 1988) and pigs (Howard and Ford, 1992). However, this is not a consistent finding since some workers have found no correlation between follicle size and IGF-1 concentrations (sheep: Monget et al., 1993; pigs: Veldhuis et al., 1986; cows: Rutter and Manns, 1991; humans: Geisthovel et al., 1989), while yet others have reported a positive relationship (pigs: Hammond et al., 1985; humans: Eden et al., 1988). Such discrepancies are difficult to reconcile and do not necessarily mean that IGF-1 has no role in follicular development. They may be due to between species differences in the role of IGF-1 in follicle development, differences in patterns of follicle development as a result of the different experimental conditions employed, or variations in the efficiency of extraction of IGFBPs from follicular fluid prior to IGF-1 analysis. Such factors require further study.

The higher concentrations of IGF-1 within the follicular fluid of small follicles in the present study, together with the negative relationship between IGF-1 and oestradiol concentrations, may suggest a more active involvement of IGF-1 in the development of small follicles. However, this does not necessarily imply that IGF-1 plays no active role in the development of large follicles. For example, IGF-1 concentrations measured in large follicles were well within the range shown to be effective in stimulating both proliferation and steroidogenesis in ovine granulosa cells (Monniaux and Pisselet, 1992). Furthermore, granulosa cells obtained from large follicles respond to comparatively lower doses of IGF-1 (at least in terms of steroidogenesis) compared with those obtained from small follicles (Monniaux and Pisselet, 1992). In addition, IGF-1 in follicular fluid measured in the present study was total content, and it is not clear that how much of this was biologically available to the granulosa cells in small compared to large follicles, particularly in view of the different array and quantities of binding proteins between small and large follicles. Moreover, the number of IGF-1 receptors in the granulosa cells from large follicles has been reported to be lo-15 fold greater than those in small follicles (Spicer et al., 1994). Based on all of these findings, it is possible that although the total amount of IGF-1 may be less in follicular fluid from large oestrogenic follicles, comparatively more of it may be biologically available to an increased number of receptors to carry out its functions. Consistent with this suggestion is the demonstration that IGF-1 mRNA declines while IGF-1 receptor mRNA increases as granulosa cells differentiate (Zhou et al., 1991).

In this study, the relationships between IGFBPs and different physiological stages of follicular development with particular regard to steroidogenic status of ovine follicular fluid revealed both qualitative and quantitative differences in IGFBP profiles. Band intensity of presumed IGFBP3 (44-42 kDa) was significantly higher in oestrogenic follicles, whereas band intensity of presumed IGFBP2 (35-34 kDa) was significantly higher in non-oestrogenic follicles. Moreover, low molecular weight IGFBPs (31-28.5


kDa) were totally undetectable in oestrogenic follicles but were present in some of the small, non-oestrogenic follicles. Monget et al. (1993) have also reported similar relationships between ovine follicular fluid concentrations of IGFBPs and follicle size.

The fact that follicular fluid IGFBPs change both qualitatively and quantitatively in relation to physiological status suggests that IGFBPs may be involved in the control of follicular development in sheep. Although, it is difficult to determine from the present results the precise role of these IGFBPs in the process of folliculogenesis, previous studies on rat granulosa cells have indicated that in vitro treatment of such cells with IGFBP2 (Bicsak et al., 1990) or IGFBP3 (Vi et al., 1989; Bicsak et al., 1990) resulted in the inhibition of aromatase activity. Moreover, intra-bursal administration of IGFBP3 caused inhibition of ovulation in rats (Bicsak et al., 1991). Such an inhibitory role for IGFBP2 is consistent with the observed inverse relationship found between presumed IGFBP2 concentrations (the band at 35 kDa) and the oestrogenic status of individual follicles in the present study. However, the presence of IGFBP3 (44-42 kDa) in significantly higher quantities in oestrogenic follicles can not be explained on the basis of its role as an inhibitor of aromatase activity. IGFBP3 in oestrogenic follicles may therefore play another role in follicle development, such as acting as a reservoir for IGF-1 or by altering the transport of IGF-1 to its cell surface receptor (Adashi et al., 1990; Clemmons, 1990). In this way it may serve to ensure a high level of exposure of ovarian cells to IGF-1. Indeed, IGFBP3 (44-42 kDa) has already been reported to increase IGF-1 binding to the membrane surface via increased membrane-associated IGFBP3 rather than through increased binding by type 1 IGF receptors. Consequently different IGFBPs may have quite different roles to play during follicular development, with some antagonising and others promoting the effects of IGF-1 within the follicle. Such possibilities clearly require further study.

The possible source of IGFBPs in ovine follicular fluid is not entirely clear, and IGFBP production by ovine granulosa cells cultured in vitro is not well documented. Limited evidence (Perks et al., 1994) has shown that expression of the IGFBP2 gene in small ovine follicles is significantly higher compared with that in large ones, and this is consistent with the findings of present study. However, these workers were unable to find any expression of the IGFBP3 gene within the ovine ovary. The significantly higher concentrations of IGFBP3 found in follicular fluid from oestrogenic follicles in the present study is, therefore, difficult to reconcile with the findings of Perks et al. (19941, but two possibilities exist. First, it is possible that the technique used to monitor IGFBP3 gene expression was not sufficiently sensitive, or secondly IGFBP3 could be of extra-ovarian/endocrine origin, with higher quantities resulting simply from increased diffusion into the enlarging follicles. However, the possibility of an endocrine origin for IGFBP3 in sheep seems highly unlikely particularly since ovarian expression of the IGFBP3 gene has been reported to be tissue specific in other species including the rat (Nakatani et al., 19911, pig (Samaras et al., 1992) and human (Guidice et al., 1991).

The factors affecting the regulation of IGFBP production in the ovine follicular fluid are also not clear. However, the results of this study suggest that IGFBPs may be regulated differently in oestrogenic compared with non-oestrogenic follicles, and this is in accord with other findings. For example, the in vivo treatment of prepubertal gilts with growth hormone increased follicular fluid IGFBP3 concentrations without having

M. Khaki, W. Haresign/Animal Reproduction Science 41 11996) 119-129 127

any effect on IGFBP2, whereas treatment of similar animals with pregnant mares’ serum gonadotropin (PMSG) did not affect IGFBP3 but decreased IGFBP2 (Samaras et al., 1994). Moreover, different hormones may either stimulate or inhibit IGFBP production. Using in vitro porcine granulosa cell cultures, both insulin and IGF-1 have been shown to stimulate the production of IGFBP2 and IGFBP3 (Grimes and Hammond, 19921, whereas FSH has been shown to dramatically inhibit the production of the same BPS (Grimes et al., 1992). Furthermore, FSH can induce a protease which will degrade low molecular weight IGFBPs (Ling et al., 19931, and this is consistent with the absence in the present study of any low molecular weight IGFBPs in the follicular fluid from large oestrogenic follicles which are known to contain high levels of gonadotrophin receptors.

In conclusion, the present study has provided information indicating quantitative changes in both IGF-1 and IGFBPs in the follicular fluid as sheep follicles developed from a small, non-oestrogenic state to a large, oestrogenic one. Such changes suggest that the role of the IGF-1 system as a local regulator of follicular activity changes as follicles develop and mature. While the IGF-I system is quite dynamic, the factors responsible for the in vivo regulation of both IGF-1 and IGFBP remain to be determined.

Acknowledgements

The authors wish to thank the Ministry of Agriculture Fisheries and Food for financial support, and Dr S Spencer (MAFIech, New Zealand) for supplies of the IGF-1 antiserum.

References

Adashi, E.Y., Resnick, C.E., D’Ercole, A.J., Svoboda, M.E. and van Wyk, J.J., 1985. Insulin-like growth factors as intraovarian regulators of granulosa cell growth and function. Endocrine Rev., 6: 400-420.

Adashi, E.Y., Resnick, C.E., Hemandez, E.R., Hurwitz, A. and Rosenfeld, R.G., 1990. Ovarian granulosa cell-derived insulin-like growth factor (IGF) binding proteins: release of low molecular weight, high affinity IGF-selective species. Mol. Cell. Endocrinol., 74: 175% 184.

Amsterdam, A. and Rotmensch, S., 1987. Structure-function relationships during granulosa cell diffetentia- tion. Endocrine Rev., 8: 309-337.

Bicsak, T.A., Shimonaka, M., Malkowski, M. and Ling, N., 1990. Insulin-like growth factor binding protein (IGF-BP) inhibition of granulosa cell function: effect on cyclic adenosine 3’,5’-monophosphate, deoxyri- bonucleic acid synthesis, and comparisons with the effect of antibody. Endocrinology, 126: 2184-2189.

Bicsak, T.A., Ling, N. and de Paolo, L.V., 1991. Ovarian intrabursal administration of insulin-like growth factor binding protein inhibits follicle rupture in gonadotropin-treated immature female rats. Biol. Reprod., 44: 599-603.

Clemmons, D.R., 1990. Insulin-like growth factor binding proteins. Trends Endocrinol. Metab., 1: 412-417. Clemmons, D.R., 1992. IGF binding proteins: regulation of cellular actions. Growth Reg., 2: 8087. Daughaday, W.H., Mariz, I.K. and Blethen, S.L., 1980. Inhibition of access bound somatomedin to membrane

receptor and immunobinding sites: a comparison of radioreceptor and radioimmunoassay of somatomedin in native and acid-ethanol-extracted serum. J. Clin. Endocrinol. Metab., 5 1: 781-788.

Davoren, J.B., Hsueh, A.J.W. and Li, C.H., 1985. Somatomedin C augments FSH-induced differentiation of cultured rat granulosa cells. Am. J. Physiol., 249: E26-33.

128 M. Khalid, W. Haresign / Animal Reproduction Science 41 (1996) 119-129

Dorington, J.H., Mckeracher, H.L., Chart, A.K. and Gore-Langton, R.E., 1983. Hormonal interactions in the control of granulosa cell differentiation. J. Steroid Biochem., 19: 17-32.

Drop, S.L.S., Brinkman, A., Kortleve, D.J., Groffen, C.A.H., Schuller, A. and Zwarthoff, E.C., 1991. The evolution of the insulin-like growth factor binding protein family. In: E.M. Spencer (Editor), Modem Concepts of Insulin-like Growth Factors. Elsevier, New York, pp. 3 I l-328.

Echtemkamp, SE., Spicer, L.J., Gregory, K.E., Canning, S.F. and Hammond, J.M., 1990. Concentrations of insulin-like growth factor-l in blood and ovarian follicular fluid of cattle selected for twins. Biol. Reprod., 43: 8-14.

Eden, J.A., Jones, J., Carter, G.D. and Alaghband-Zadeh, J., 1988. A comparison of follicular fluid levels of insulin-like growth factor-l in normal dominant and cohort follicles, polycystic and multicystic ovaries. Clin. Endocrinol. (Oxford), 29: 327-336.

Foxcroft, G.R., Shaw, H.J., Hunter, M.G., Booth, P.J. and Lancaster, R.T., 1987. Relationships between luteinizing hormone, follicle stimulating hormone and prolactin secretion and ovarian follicular development in the weaned sow. Biol. Reprod., 36: 175-191.

Geisthovel, F., Moretti-Rojas, I.M., Rojas, F.J. and Asch, R.H., 1989. Immunoreactive insulin-like growth factor-I in human follicular fluid. Hum. Reprod., 4: 35-38.

Grimes, R.W. and Hammond, J.M., 1992. Insulin and insulin-like growth factors (IGFs) stimulate production of IGF-binding proteins by ovarian granulosa cells. Endocrinology, 13 1: 553-558.

Grimes, R.W., Samaras, S.E., Barber, J.A., Shimasaki, S., Ling, N. and Hammond, J.M., 1992. Gonadotropin and CAMP modulation of IGF binding protein production in ovarian granulosa cells. Am. J. Physiol., 262: E497-E503.

Guidice, L.C., Milki, A.A., Milkowski, D.A. and Danasouri, I.E., 1991. Human granulosa cells contain messenger ribonucleic acids encoding insulin-like growth factor binding proteins (IGFBPs) and secrete IGFBPs in culture. Fertil. Steril., 56: 475-480.

Hammond, J.M., Baranao, J.L.S., Skaleris, D., Knight, A.B., Romanus, J.A. and Rechler, M.M., 1985. Production of insulin-like growth factors by ovarian granulosa cells. Endocrinology, 117: 2553-2555.

Haresign, W., Basiouni, G.F. and Khalid, M., 1994. Progesterone pre-treatment alters steroid secretion rates and follicular fluid IGF-1 concentrations in seasonally anoestrous ewes treated with GnRH. J. Reprod. Fertil. Abstr. Ser. No. 14, Abstr. No. 23.

Hossenlopp, P., Seurin, D., Segovia-Quinson, B., Hardouin, S. and Binoux, M., 1986. Analysis of serum insulin-like growth factor binding proteins using Western blotting: use of the method for titration of the binding proteins and competitive binding studies. Anal. B&hem., 154: 138-143.

Howard, H.J. and Ford, J.J., 1992. Relationships among concentrations of steroids, inhibin, insulin-like growth factor-l (IGF-I), and IGF-binding proteins during follicular development in weaned sows. Biol. Reprod., 47: 193-201.

Hsueh, A.J.W., Adashi, E.Y., Jones, P.B.C. and Welsh, T.H., 1984. Hormonal regulation of the differentiation of cultured ovarian granulosa cells. Endocrine Rev., 5: 76- 127.

Ling, N.C., Liu, X.J., Malkowski, M., Guo, Y.L., Erickson, G.F. and Shimasaki, S., 1993. Structural and functional studies of insulin-like growth factor binding proteins in the ovary. Growth Regul., 3: 70-74.

Maruo, T.. Hayashi, M., Matsuo, H., Ueda, Y., Morikawa, H. and Mochizuki, M., 1988. Comparison of the facilitative roles of insulin and insulin-like growth factor-l in the functional differentiation of granulosa cells, in vitro porcine model. Acta Endocrinol. (Copenhagen), 117: 230-240.

McNeilly, A.S., Picton, H.M., Campbell, B.K; and Baird, D.T., 1991. Gonadotrophic control of follicle growth in the ewe. J. Reprod. Fertil. Suppl., 43: 177- 186.

Meurer, K.A., Cox, N.M., Matamoros, LA. and Tubbs, R.C., 1991. Decreased follicular steroids and insulin-like growth factor-l and increased atresia in diabetic gilts during follicular growth stimulated with PMSG. J. Reprod. Fertil., 91: 187-196.

Mondschein, J.S., Etherton, T.D. and Hammond, J.M., 1990. Characterization of insulin-like growth factor-binding proteins of porcine ovarian follicular fluid. Biol. Reprod., 44: 315-320.

Monget, P., Monniaux, D., Pisselet, C. and Durand, P., 1993. Changes in insulin-like growth factor-I (IGF-I), IGF-II, and their binding proteins during growth and atresia of ovine ovarian follicles. Endocrinology, 132: 143881446.

Momtiaux, D. and Pisselet, C., 1992. Control of proliferation and differentiation of ovine granulosa cells by insulin-like growth factor-I and follicle-stimulating hormone in vitro. Biol. Reprod., 46: 109- 119.

M. Khalid, W. Harcsign/Animal Reproduction Science 41 (1996) 119-129 129

Nakatani, A., Shimasaki, S., Erickson, G.F. and Ling, N., 1991. Tissue-specific expression of four insulin-like growth factor-binding proteins (1, 2, 3 and 4) in the rat ovary. Endocrinology, 129: 1521-1529.

Perks, C.M., Stevenson, K.R. and Wathes, D.C., 1994. Localization of insulin-like growth factor binding proteins 2 & 3 (IGFBPs 2 & 3) in the ovine ovary. J. Reprod. Fertil., Abstr. Ser. No. 14, Abstr. No. 4.

Purvis, K., Illius, A.W. and Haynes, N.B., 1974. Plasma testosterone concentrations in the ram. J. Endocrinol., 61: 243-253.

Richards, J.S., 1980. Maturation of ovarian follicles: actions and interactions of pituitary and ovarian hormones on follicular cell differentiation. Physiol. Rev., 60: 51-89.

Rutter, L.M. and Manns, J.G., 1991. Insuhn-like growth factor-l in follicular development and function in postpartum beef cows. J. Anim. Sci., 69: 1140-l 146.

Samaras, S.E., Hagen, D.R., Shimasaki, S., Ling, N. and Hammond, J.M., 1992. Expression of insulin-like growth factor-binding protein-2 and -3 messenger ribonucleic acid in the porcine ovary: localization and physiological changes. Endocrinology, 130: 2739-2744.

Samaras, S.E., Hagen, D.R., Bryan, K.A., Mondschein, J.S., Canning, S.F. and Hammond, J.M., 1994. Effects of growth hormone and gonadotropin on insulin-like growth factor system in the porcine ovary. Biol. Reprod., 50: I78- 186.

Schams, D., 1987. Luteal peptides and intracellular communication. J. Reprod. Fertil. Suppl., 34: 87-99. Spicer, L.J. and Emight, W.J., 1991. Concentrations of insulin-like growth factor-l in follicular fluid of bovine

ovarian follicles: Effect of daily injections of a growth hormone-releasing factor analog and(or) thy- rotropin-releasing hormone. J. Anim. Sci., 69: 1133- 1 139.

Spicer, L.J., Echtemkamp, SE., Canning, S.F. and Hammond, J.M., 1988. Relationships between concentrations of immunoreactive insulin-like growth factor-l in follicular fluid and various biochemical markers of differentiation in bovine antral follicles. Biol. Reprod., 39: 573-580.

Spicer, L.J., Alpizar, E. and Vernon, R.K., 1994. Insulin-like growth factor-l receptors in ovarian granulosa cells: Effect of follicle size and hormones. Mol. Cell. Endocrinol., 102: 69-76.

Ui, M., Shimonaka, M., Shimasaki, S. and Ling, N., 1989. An insulin-like growth factor-binding protein blocks follicle-stimulating hormone-stimulated steroid production by ovarian granulosa cells. Endocrinol- ogy, 125: 912-916.

Veldhuis, J.D., Rodgers, R.J., Azimi, P., Garmey, J., Juchter, D. and May, W., 1987. Mechanisms subserving the steroidogenic synergism between follicle-stimulating hormone and insulin-like growth factor-l (somatomedin C): alterations in cellular sterol metabolism in swine granulosa cells. J. Biol. Chem., 262: 7658-7664.

Veldhuis, J., Rodgers, R.J. and Furhmetto, R.W., 1986. Synergistic actions of estradiol and the insulin-like growth factor, somatomedin-C, on swine ovarian (granulosa) cells. Endocrinology, 119: 530-538.

Zhou, J., Chin, E. and Bondy, C., 1991. Cellular pattern of insulin-like growth factor-I (IGF-I) and IGF-I receptor gene expression in the developing and mature ovarian follicle. Endocrinology, 129: 328 l-3288.

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