Archives of Medical Research 38 (2007) 392e397

ORIGINAL ARTICLE

Gastric Emptying Effect by 4-Aminopyridine in Patientswith Chronic Spinal Cord Injury

Israel Grijalva,a Gabriel Guızar-Sahagun,a,c Delia Rodrıguez-Pacheco,b Carlos Francisco-Arguelles,b

Gilberto Castaneda-Hernandez,d and Jose Antonio Palma-Aguirreb

aMedical Research Unit for Neurological Diseases, bDepartment of Pharmacology, Hospital de Especialidades,

Centro Medico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, Mexico City, MexicocProyecto Camina, A.C., Mexico City, Mexico

dExternal Pharmacology Section, Centro de Investigaciones y Estudios Avanzados, Instituto Politecnico Nacional, Mexico City, Mexico

Received for publication June 24, 2006; accepted November 29, 2006 (ARCMED-D-06-00256).

Background. 4-Aminopyridine (4-AP) given to patients with chronic spinal cord injury(SCI) has shown beneficial effects in some somatic and autonomic functions, althoughpatients often develop dyspeptic symptoms. 4-AP is a potassium-channel blocker capableof altering gastro-pyloric functions as demonstrated experimentally. Our objective was toexamine the influence of 4-AP treatment on gastric emptying in patients with chronic SCI.

Methods. Gastric emptying was measured by the acetaminophen absorption test in 18 pa-tients (9 with cervical and 9 with thoracic injury), and 9 healthy volunteers. Patientsreceived increasing oral doses, 5 mg day�1 of oral 4-AP (5e30 mg day�1), for 12 weeks.Patients were studied before and at the end of the last week of 4-AP treatment, whereashealthy volunteers (without 4-AP treatment) were studied only once. Whole blood sam-ples of 2.5 mL were drawn at 0 (before 1 g of oral acetaminophen) and at 15, 30, 45, 60,75, 90, 105 and 120 min postdose. Acetaminophen concentration in plasma was deter-mined by high-pressure liquid chromatography.

Results. Treatment with 4-AP significantly delayed stomach emptying in patients withchronic SCI, considering the significant decreasing of acetaminophen absorption (t pairedtest, p !0.05). This effect did not correlate either to the level or ASIA score of the injury(linear regression correlation analysis, r2 5 0.003 and 0.015, respectively). No significantdifferences were observed by comparing data of patients before 4-AP treatment withhealthy volunteers.

Conclusions. 4-AP intake in patients with chronic spinal cord injury significantly slowedgastric emptying regardless of level and ASIA score of the injury. � 2007 IMSS. Pub-lished by Elsevier Inc.

Key Words: Acetaminophen absorption test, Autonomic nerve conduction, Paraplegia, Potassiumchannel blocking.

Introduction

Previous reports support the fact that 4-aminopyridine(4-AP) is a pharmacological agent capable of restoringsome neural conduction (1,2) and improving motor andsensory functions in selected patients with chronic spinalcord injury (SCI) (3e6).

Address reprint requests to: Israel Grijalva, UIME Neurologicas, Cal-

zada de Tlalpan 4430, Col. Toriello Guerra. Mexico, D.F. 14050, Mexico;

E-mail: igrijalvao@yahoo.com

0188-4409/07 $esee front matter. Copyright � 2007 IMSS. Published by Edoi: 10.1016/j.arcmed.2006.11.007

SCI affects not only voluntary motor and sensory func-tions below the cord level; it also alters autonomic func-tions, resulting in multiple systemic and metabolicdisturbances (7e10). Abnormalities in gastrointestinal mo-tility, particularly delay of gastric emptying, are commoncomplications after acute and chronic stages of SCI andare closely related to autonomic dysfunction (11e15).

4-AP given to patients with chronic SCI has shown ben-eficial effects on some autonomic functions, particularly onlungs (16) and heart (17,18). However, possible effects of

lsevier Inc.

393Gastric Emptying Effect by 4-AP in SCI Patients

4-AP on gastrointestinal function in such patients have notpreviously been explored.

Biochemical and electrophysiological studies haveshown that a diversity of potassium channels are presentin gastric muscle as well as in myenteric neurons. Potas-sium currents through these channels are important regula-tors of gastric tone and motility (19e22).

4-AP is the classic nonselective pharmacological blockerof voltage-gated potassium channels (23,24). Preliminaryexperimental studies have demonstrated that 4-AP modifiessome physiological gastrointestinal processes (25e29),which can result in slowing gastrointestinal transit (30).

The purpose of the present study was to determine theinfluence of 4-AP on gastric emptying in patients withchronic SCI. Taking into account basic experimental re-ports regarding the effects of 4-AP on gastrointestinal func-tion, as well as the association between 4-AP intake andgastric symptoms reported in some clinical studies (6),we hypothesized that this agent given to our patients couldslow gastric emptying. As an alternative hypothesis,we proposed that 4-AP could improve gastric emptying asa result of improved autonomic nerve conduction. To testour hypotheses, we chose a validated method to assessgastric emptying, namely, the acetaminophen absorptiontest (31,32).

Materials and Methods

To assess the influence of 4-AP on gastric emptying time inpatients with chronic SCI, a comparative open labeled clin-ical trial was performed. Patients were recruited from theMedical Research Unit for Neurological Diseases of theSpecialties Hospital, Centro Medico Nacional Siglo XXI,Instituto Mexicano del Seguro Social, Mexico City. Thestudy was carried out in accordance with the recommenda-tions of the Declaration of Helsinki and approved by thehospital Medical Ethics and Research Committee. Allhealthy volunteers and patients gave written informed con-sent for participation.

Gastric emptying was evaluated using the acetamino-phen absorption test (31,32). The absorption of a 1 g fastingdose of oral solution of acetaminophen was studied in 9healthy volunteers and 18 SCI patients. Healthy volunteersserved as controls for normal gastric function and were nottreated with 4-AP; they were subjected to the gastric emp-tying study only once, whereas acetaminophen absorptionstudies were performed twice in SCI patients: the first be-fore 4-AP treatment and the second 12 weeks after 4-APtreatment. SCI patients received oral doses of 4-AP startingat 5 mg day�1, increasing 5 mg per day every week untila dose of 30 mg day�1 was reached in a 6-week period. Pa-tients then received 30 mg day�1 (10 mg each 8 h [6:00,14:00 and 22:00 h]) for 6 weeks. The 4-AP was given asan immediate-release formulation using gelatin capsules

containing 4-AP 5 mg and microcrystalline cellulose asthe excipient. Capsules were prepared at our facilities.The day of the second acetaminophen absorption test (start-ing at 8:00 AM), patients omitted intake of the correspond-ing dose of 4-AP to avoid any interaction with the singledose of acetaminophen given for the study.

Subjects

Table 1 shows spinal cord injury/completeness levels of pa-tients subjected to the study. Age range of healthy male/fe-male volunteers was 18e40 years. Patients of both genderswere from 23 to 48 years old with both complete and in-complete injury and injury levels from C4 to T8; timeelapsed after injury was from 1.5e15 years (mean �SD:7.1 � 3.2 years).

Inclusion criteria were as follows: tetraplegia or paraple-gia for O1.5 years before the study began, aged 18e60years, medically stable and able to breathe independently,stable neurological deficits for O90 days before the study,absence of epileptic history and electroencephalogramwithout epileptic activity. Women had to be postmeno-pausal, surgically sterile, or using an acceptable methodof birth control. Exclusion criteria were as follows: pressureulcers, skin infections, or phlebitis; history of cardiovascu-lar disease; systolic blood pressure O150 or !70 mmHg,diastolic blood pressure O110 or !50 mmHg, or heart rateO110 or !50 beats/min; impaired hepatic function (totalhepatic enzyme or bilirubin levels greater than two timesthe upper limit of normal) or impaired renal function (cre-atinine level greater than two times the upper limit of

Table 1. Demographic and injury characteristics of study patients

(listed according to injury level)

Patient Age Gender

Post-injury

time

(years)

Type of

injury

Injury

level AIS

1 29 Male 11 BA C4 B

2 33 Female 10 MVA C4 B

3 35 Male 7 Diving C4 C

4 40 Male 10 MVA C4 A

5 48 Male 10 MVA C4 B

6 23 Male 1.5 Diving C5 B

7 25 Male 6 Fall C5 B

8 43 Male 15 MVA C5 D

9 29 Male 3 Diving C6 C

10 42 Male 7 Fall T1 D

11 26 Male 4 Gun shot T2 C

12 44 Male 6 Gun shot T2 B

13 35 Male 9 Gun shot T5 B

14 30 Female 11 MVA T5 A

15 44 Female 6 Gun shot T5 C

16 42 Male 6 MVA T6 B

17 23 Male 2.5 Gun shot T7 C

18 25 Female 7 Fall T8 B

AIS, ASIA impairment scale; BA, bicycle-riding accident; MVA, motor

vehicle accident.

394 Grijalva et al. / Archives of Medical Research 38 (2007) 392e397

normal) !6 months before the study; known allergy to pyr-idine-containing drugs; neurological, degenerative, or psy-chiatric disorders that would impair the patient’s ability tocomplete the protocol; any illness or abnormality thatwould jeopardize patient safety or interfere with the con-duct of the study; history of substance abuse; and inabilityto discontinue excluded concomitant drug therapy. Patientsalso were excluded if they were receiving treatment with anantispasticity compound and could not maintain a stabledaily dosage, were pregnant or lactating, had received anyother investigational drug !30 days before the study, orhad received any drug known to cause significant majororgan toxicity !3 months before the study.

Plasma Collection and Analysis

After 10 h fasting conditions, a heparinized, indwelling ve-nous cannula was placed in a dorsal vein of the forearm topermit sampling of blood for analysis of plasma concentra-tions of acetaminophen. Whole blood samples of 2.5 mLwere withdrawn at 0 (before acetaminophen dose) and at15, 30, 45, 60, 75, 90, 105 and 120 min postdose.

Each blood sample was drawn into a test tube containingsodium heparin and immediately tilted gently 6 to 10 timesto mix the blood and heparin (in order to prevent coagula-tion). Within 10 to 20 min, the sample was centrifuged at1200 rpm for 10 min. The plasma was then transferred intoa plastic vial, labeled, packed in dry ice, and stored at�70�C until analysis.

Acetaminophen concentration in plasma was determinedby a high-pressure liquid chromatography assay with UVdetection according to the methodology by Garcıa-Lopezet al. (33).

Individual plasma acetaminophen concentration vs.time curves were constructed, and conventional pharmaco-kinetic parameters such as maximum plasma concentration(Cmax) as well as the time to reach this maximum (tmax)were directly determined from these plots. The area underthe concentration-time curve (AUC) was estimated by thetrapezoid rule. A paired t-test was used for comparison ofthe results in SCI subjects between pre- and post-4AP-treatment. Comparison between control and SCI basal

measures were also performed by Students t-test in orderto detect possible alterations attributable to the SCI. Usinglinear regression analysis, we correlated AUC (differencesbetween pre- and post-treatment with 4-AP) to the level ofinjury and to the ASIA (American Spinal Injury Associa-tion) impairment scale. The pharmacokinetic and linearregression analysis were performed with the SPSS version10 and the GraphPad Prism version 3.02 software,respectively. Statistical significance was considered to bep !0.05.

Results

Results are summarized in Table 2. Gastric emptying ap-peared to be normal in patients with chronic SCI before4-AP treatment, taking into account that comparisons be-tween control and SCI basal measures were not significant.4-AP treatment significantly delayed gastric emptying,compared with results of the same patients before 4-APtreatment, as demonstrated by decreased acetaminophenabsorption after 4-AP treatment, with both Cmax and AUCvalues ( p !0.05). tmax remained unchanged. 4-AP treat-ment delayed gastric emptying by |20 and 31% in cervicaland thoracic patients, respectively. AUC changes after 4-APtreatment were independent of both the level of injury andthe ASIA impairment scale (r2 5 0.003 and 0.015, respec-tively, Figure 1).

Discussion

Our aim was to assess the effect of 12-week treatment with4-AP on gastric emptying of patients with chronic SCI. Weused the acetaminophen absorption technique, which offersa relatively simple and inexpensive technique that yields anindirect quantitative measurement of gastric emptying asverified by the scintigraphic emptying of liquid and solidmeals (31,32). Our main results deal with reduction in gas-tric emptying induced by 4-AP in patients with SCI at bothcervical and thoracic levels.

We observed that 4-AP treatment significantly decreasedacetaminophen Cmax and AUC values, while tmax valuesremained without changes. This pattern of changes suggests

Table 2. Pharmacokinetic parameters of a single dose of 1 g of oral acetaminophen solution before and after 12 weeks of 4-AP treatment

in patients with chronic spinal cord injury

Pre-treatment Post-treatment (4-AP)

Group n Cmax (mg/mL) tmax (min) AUC(0e2 h) mg/mL/min n Cmax (mg/mL) tmax (min) AUC(0e2 h) mg/mL/min

Patients 18 13.26 � 1.01 45.83 � 5.88 900.3 � 71.55 18 *10.55 � 0.93 45.81 � 3.92 *661.6 � 56.11

Control 9 13.30 � 0.70 42.00 � 5.10 895.0 � 123.8

Healthy volunteers without 4-AP were used as controls.

Cmax 5 maximum plasma concentration; tmax 5 time to reach maximum plasma concentration; AUC 5 area under the plasma concentration-time curve. Data

represent mean � standard error of the mean.

*Significant differences against pre-treatment ( p !0.05).

395Gastric Emptying Effect by 4-AP in SCI Patients

that 4-AP effect on acetaminophen absorption was due toa delayed gastric emptying. A tmax change could be ex-pected if two different acetaminophen formulations werecompared. If one formulation releases the drug faster thanthe other, the amount of drug arriving to the duodenum atshort times will be higher than with the other slow-releasingformulation. Thus, differences in tmax will be observed.

However, in our study, the same acetaminophen formu-lation, a solution, was used under two different conditions.Thus, there were no differences due to drug release, as thedrug is already dissolved. Hence, if gastric emptying is de-layed, and this is the only factor that plays a significant rolein drug absorption, a slower absorption is expected in thepresence of 4-AP. That is, a lower amount of drug will ar-rive to the duodenum at every sampling time. Therefore, theabsorption rate will not be slower at shorter times and fasterat longer times. It will be slower at all times. Hence, therewill be a lower plasma concentration at all sampling timeswithin the 2-h sampling period, but no shift in tmax.

Even though 4-AP has been tested in several studies ofSCI and multiple sclerosis, there are no previous reports re-garding its effect on gastrointestinal functions, althoughfrequent gastric irritation and other symptoms associated

Figure 1. Linear regression correlation analysis of the area under the

concentration-time curve (AUC) with both injury level and to ASIA

impairment scale (AIS). Points represent differences between baseline

(pre-treatment) and final (after 4-AP treatment) values of each studied

patient. There was no correlation between either the level of injury

(r2 5 0.0007) or the AIS impairment scale (r2 5 0.015).

with gastric dysfunction have been reported for patientsreceiving 4-AP (6).

The lack of correlation between AUC changes with boththe level of injury and the ASIA impairment scale suggeststhat direct influence of 4-AP on physiological gastric func-tion, regardless of neurological integrity, is the main causeof the adverse effect we observed. If so, such an effectcould be present in patients treated with 4-AP for otherdiseases, or even in healthy subjects.

The effect of 4-AP on gastric emptying of healthy con-trols was not assessed in this study, taking into account eth-ical issues, particularly the possibility of producing painfuladverse effects. However, experimental studies clearlyshow that 4-AP given orally inhibited gastrointestinal pro-pulsion of a charcoal suspension in healthy conscious mice(30).

To better understand our results, it is important to reviewsome data obtained from basic research. The physiologicalmechanisms that regulate gastric tone and motility are verycomplex. Adequate gastric emptying requires diverse neu-rohumoral events, which act in a coordinated mannerresulting in contraction of antral smooth muscles and relax-ation of the pylorus. Cholinergic and adrenergic, as well asnon-adrenergic, non-cholinergic neurotransmission playimportant roles in regulating contraction and relaxation ofthe gastrointestinal tract.

We propose that 4-AP at doses and times used here willdiminish potassium current properties in gastric muscle andmyenteric neurons, contribute to altering gastric emptying,and may lead to development of dyspeptic symptoms. 4-APis a known potassium-channel blocker (34). Taking intoaccount such a property, it has been used as a pharmacolog-ical tool in multiple studies on gastric function. 4-APinduces electrical and contractile activities on gastricmuscles of the cat (25), blocks voltage-sensitive transientpotassium current in stomatogastric neurons of the lobster,interferes with the pyloric motor rhythm (26), diminishesb3-adrenoceptor-mediated relaxations in guinea pig gastro-intestinal muscle (27), blocks A-type currents (due to Kv4channels) in murine antral muscle, alters the negativeresting membrane potentials (28), and stimulates gastricsecretion in rat (29).

4-AP also increases the release of several neurotransmit-ters including acetylcholine (35), noradrenaline (36), dopa-mine (37,38), and serotonin (39), all closely related togastrointestinal motility (40).

On the other hand, NO neurotransmission influencesgastric emptying and transpyloric flow by altering the pylo-ric tone (41,42). The effects induced by NO in differenttissues depend on direct and/or indirect interactions withpotassium channels. The blockage of potassium channelsproduced by 4-AP inhibits the neuromuscular effects in-duced by NO (43).

In conclusion, the present study extends the knowledgeregarding the effects of 4-AP on gastrointestinal motility

396 Grijalva et al. / Archives of Medical Research 38 (2007) 392e397

in patients with SCI and suggests that the significantlydelayed gastric emptying we described could be relatedto adverse gastrointestinal symptoms reported for somepatients treated with 4-AP.

AcknowledgmentsThe study was supported by the Instituto Mexicano del SeguroSocial and the Centro de Investigaciones y Estudios Avanzadosdel Instituto Politecnico Nacional, Mexico City, Mexico.

The authors thank Susan Holmes for helpful review of themanuscript.

References1. Shi R, Kelly TM, Blight AR. Conduction block in acute and chronic

spinal cord injury: different dose-response characteristics for reversal

by 4-aminopyridine. Exp Neurol 1997;148:495e501.

2. Wolfe DL, Hayes KC, Hsieh JT, Potter PJ. Effects of 4-aminopyridine

on motor evoked potentials in patients with spinal cord injury: a

double-blinded, placebo-controlled crossover trial. J Neurotrauma

2001;18:757e771.

3. Hansebout RR, Blight AR, Fawcett S, Reddy K. 4-Aminopyridine in

chronic spinal cord injury: a controlled, double-blind, crossover study

in eight patients. J Neurotrauma 1993;10:1e18.

4. Potter PJ, Hayes KC, Segal JL, Hsieh JT, Brunnemann SR, Delaney GA,

et al. Randomized double-blind crossover trial of fampridine-SR (sus-

tained release 4-aminopyridine) in patients with incomplete spinal cord

injury. J Neurotrauma 1998;15:837e849.

5. Segal JL, Pathak MS, Hernandez JP, Himber PL, Brunnemann SR,

Charter RS. Safety and efficacy of 4-aminopyridine in humans with

spinal cord injury: a long-term, controlled trial. Pharmacotherapy

1999;19:713e723.

6. Grijalva I, Guizar-Sahagun G, Castaneda-Hernandez G, Mino D,

Maldonado-Julian H, Vidal-Cantu G, et al. Efficacy and safety of 4-

aminopyridine in patients with long-term spinal cord injury: a random-

ized, double-blind, placebo-controlled trial. Pharmacotherapy 2003;

23:823e834.

7. Cruse JM, Keith JC, Bryant ML Jr, Lewis RE Jr. Immune system-

neuroendocrine dysregulation in spinal cord injury. Immunol Res

1996;15:306e314.

8. Guizar-Sahagun G, Castaneda-Hernandez G, Garcia-Lopez P, Franco-

Bourland R, Grijalva I, Madrazo I. Pathophysiological mechanisms in-

volved in systemic and metabolic alterations secondary to spinal cord

injury. Proc West Pharmacol Soc 1998;41:237e240.

9. Teasell RW, Arnold JM, Krassioukov A, Delaney GA. Cardiovascular

consequences of loss of supraspinal control of the sympathetic nervous

system after spinal cord injury. Arch Phys Med Rehabil 2000;81:

506e516.

10. Bauman WA, Spungen AM. Metabolic changes in persons after spinal

cord injury. Phys Med Rehabil Clin N Am 2000;11:109e140.

11. Guizar-Sahagun G, Garcia-Lopez P, Espitia AL, Mendez S, Castaneda-

Hernandez G, Madrazo I, et al. Histochemical evidence of the increased

expression of nicotinamide adenine dinucleotide phosphate-dependent

diaphorase in neurons of the myenteric plexus after acute spinal cord

injury in adult rats. Neurosci Lett 1996;206:185e188.

12. Kao CH, Ho YJ, Changlai SP, Ding HJ. Gastric emptying in spinal

cord injury patients. Dig Dis Sci 1999;44:1512e1515.

13. Krogh K, Mosdal C, Laurberg S. Gastrointestinal and segmental

colonic transit times in patients with acute and chronic spinal cord

lesions. Spinal Cord 2000;38:615e621.

14. Gondim FA, Rodrigues CL, da Graca JR, Camurca FD, de Alencar HM,

dos Santos AA, et al. Neural mechanisms involved in the delay of gas-

tric emptying and gastrointestinal transit of liquid after thoracic spinal

cord transection in awake rats. Auton Neurosci 2001;87:52e58.

15. Rodrigues CL, Gondim F de A, Leal PR, Camurca FD, Freire CC, dos

Santos AA, et al. Gastric emptying and gastrointestinal transit of

liquid throughout the first month after thoracic spinal cord transection

in awake rats. Dig Dis Sci 2001;46:1604e1609.

16. Segal JL, Brunnemann SR. 4-Aminopyridine improves pulmonary

function in quadriplegic humans with longstanding spinal cord injury.

Pharmacotherapy 1997;17:415e423.

17. Segal JL, Warner AL, Brunnemann SR, Bunten DC. 4-aminopyridine

influences heart rate variability in long-standing spinal cord injury.

Am J Ther 2002;9:29e33.

18. Wakana CI, Segal JL. Effects of 4-aminopyridine on cardiac repolar-

ization, PR interval, and heart rate in patients with spinal cord injury.

Pharmacotherapy 2003;23:133e136.

19. Carl A, McHale NG, Publicover NG, Sanders KM. Participation of

Ca2þ-activated Kþ channels in electrical activity of canine gastric

smooth muscle. J Physiol 1990;429:205e221.

20. Duridanova DB, Gagov HS, Boev KK. Two populations of smooth

muscle cells in the guinea-pig gastric antrum. Eur J Pharmacol

1997;333:105e111.

21. Hatton WJ, Mason HS, Carl A, Doherty P, Latten MJ, Kenyon JL,

et al. Functional and molecular expression of a voltage-dependent

Kþ channel (Kv1.1) in interstitial cells of Cajal. J Physiol 2001;533:

315e327.

22. Ohya S, Asakura K, Muraki K, Watanabe M, Imaizumi Y. Molecular

and functional characterization of ERG, KCNQ, and KCNE subtypes

in rat stomach smooth muscle. Am J Physiol Gastrointest Liver Phys-

iol 2002;282:G277eG287.

23. Grissmer S, Nguyen AN, Aiyar J, Hanson DC, Mather RJ,

Gutman GA, et al. Pharmacological characterization of five cloned

voltage-gated Kþ channels, types Kv1.1, 1.2, 1.3, 1.5, and 3.1, stably

expressed in mammalian cell lines. Mol Pharmacol 1994;45:

1227e1234.

24. Mathie A, Wooltorton JR, Watkins CS. Voltage-activated potassium

channels in mammalian neurons and their block by novel pharmaco-

logical agents. Gen Pharmacol 1998;30:13e24.

25. Boev K, Bonev A, Papasova M. 4-Aminopyridine-induced changes in

the electrical and contractile activities of the gastric smooth muscle.

Gen Physiol Biophys 1985;4:589e595.

26. Tierney AJ, Harris-Warrick RM. Physiological role of the transient

potassium current in the pyloric circuit of the lobster stomatogastric

ganglion. J Neurophysiol 1992;67:599e609.

27. Horinouchi T, Tanaka Y, Koike K. Evidence for the primary role for

4-aminopyridine-sensitive Kv channels in b3-adrenoceptor-mediated,

cyclic AMP-independent relaxations of guinea-pig gastrointestinal

smooth muscles. Naunyn Schmiedebergs Arch Pharmacol 2003;367:

193e203.

28. Amberg GC, Baker SA, Koh SD, Hatton WJ, Murray KJ, Horowitz B,

et al. Characterization of the A-type potassium current in murine

gastric antrum. J Physiol 2002;544:417e428.

29. Mantovani P, Taddei E, Giachetti D. Effect of 4-aminopyridine on

gastric secretion in rats. Boll Soc Ital Biol Sper 1984;60:1381e1384.

30. Dong DL, Wang QH, Chen W, Fan JJ, Mu JW, Ke J, et al. Contrasting

effects of tetraethylammonium and 4-aminopyridine on the gastroin-

testinal function of mice. Eur J Pharmacol 2005;509:179e185.

31. Naslund E, Bogefors J, Gryback P, Jacobsson H, Hellstrom PM.

Gastric emptying: comparison of scintigraphic, polyethylene glycol

dilution, and paracetamol tracer assessment techniques. Scand J

Gastroenterol 2000;35:375e379.

32. Willems M, Quartero AO, Numans ME. How useful is paracetamol

absorption as a marker of gastric emptying? A systematic literature

study. Dig Dis Sci 2001;46:2256e2262.

397Gastric Emptying Effect by 4-AP in SCI Patients

33. Garcia-Lopez P, Perez-Urizar J, Ibarra A, Grijalva I, Madrazo I,

Flores-Murrieta F, et al. Comparison between Sprague-Dawley and

Wistar rats as an experimental model of pharmacokinetic alterations

induced by spinal cord injury. Arch Med Res 1996;27:453e457.

34. Meves H, Pichon Y. The effect of internal and external 4-aminopyri-

dine on the potassium currents in intracellularly perfused squid giant

axons. J Physiol 1977;268:511e532.

35. Damsma G, Biessels PT, Westerink BH, De Vries JB, Horn AS.

Differential effects of 4-aminopyridine and 2,4-diaminopyridine on

the in vivo release of acetylcholine and dopamine in freely moving rats

measured by intrastriatal dialysis. Eur J Pharmacol 1988;145:15e20.

36. Hu PS, Fredholm BB. 4-Aminopyridine-induced increase in basal and

stimulation-evoked [3H]-NA release in slices from rat hippocampus:

Ca2þ sensitivity and presynaptic control. Br J Pharmacol 1991;102:

764e768.

37. Scheer HW, Lavoie PA. Mechanism of aminopyridine-induced release

of [3H]dopamine from rat brain synaptosomes. Gen Pharmacol 1991;

22:169e172.

38. Dawson LA, Routledge C. Differential effects of potassium channel

blockers on extracellular concentrations of dopamine and 5-HT in

the striatum of conscious rats. Br J Pharmacol 1995;116:3260e3264.

39. Schechter LE. The potassium channel blockers 4-aminopyridine and

tetraethylammonium increase the spontaneous basal release of

[3H]5-hydroxytryptamine in rat hippocampal slices. J Pharmacol

Exp Ther 1997;282:262e270.

40. Hansen MB. Neurohumoral control of gastrointestinal motility.

Physiol Res 2003;52:1e30.

41. Lingenfelser T, Blackshaw LA, Sun WM, Dent J. Pyloric motor

response to central and peripheral nitric oxide in the ferret. Neuro-

gastroenterol Motil 1997;9:167e175.

42. Tomita R, Tanjoh K, Fujisaki S, Fukuzawa M. The role of nitric oxide

(NO) in the human pyloric sphincter. Hepatogastroenterology 1999;

46:2999e3003.

43. Queiroz RN, Ramos ER, Alves-Do-Prado W. 4-Aminopyridine

inhibits the neuromuscular effects of nitric oxide and 8-Br-cGMP.

Braz J Med Biol Res 2003;36:937e941.