Investigation of the neural target level of hyperthyroidism in premature ejaculation in a rat model of pharmacologically induced ejaculation.

INTRODUCTION: Association between hyperthyroidism and premature ejaculation was demonstrated in clinical studies. AIM: The aim of this study is to determine the target level of changes on ejaculatory physiology under hyperthyroid states. METHODS: p-Chloroamphetamine (PCA)-induced pharmacologic ejaculation model with 24 male Wistar rats was used in the study. Subcutaneous injection of L-thyroxine for 14 days was performed to induce hyperthyroidism. At the end of the injection period, thyroid hormone status was evaluated by serum thyroid-stimulating hormone measurements in all rats. At the beginning of the operations, complete spinal transections (tx) at the T8-T9 level were performed to half of the L-thyroxine-injected and control group rats. Thus, experimental groups were constructed as follows: Group 1--control-spinal intact (n=6), group 2-control-spinal tx (n=6), group 3-hyperthyroid-spinal intact (n=6), and group 4-hyperthyroid-spinal tx (n=6). Ejaculatory responses were recorded before and 30 minutes after intraperitoneal administration of 5 mg/kg PCA. MAIN OUTCOME MEASURES: During the operations, seminal vesicle (SV) catheterization and bulbospongiosus (BS) muscle dissections were performed in all rats to demonstrate SV pressure (SVP) BS electromyographic (EMG) activity changes. RESULTS: Following PCA administration SVP tonic amplitude, SV phasic contraction (SVPC) frequency, SVPC maximal amplitude, and BS EMG area under curve values were higher in hyperthyroid intact rats than in control intact rats. The time interval between PCA administration and first ejaculation of hyperthyroid intact rats were significantly shorter than control intact rats (261 ± 7.30 seconds vs. 426 ± 49.6 seconds, P=0.008). All of the changes in the ejaculatory parameters that were induced by hyperthyroidism were completely resolved after spinal transections at the T8-T9 level in group 4. CONCLUSION: In this study, we confirmed the recent data that hyperthyroidism affects both the emission and expulsion phases of ejaculation. The changes that were induced by hyperthyroidism on ejaculatory physiology probably take place in the supraspinal centers above T8 level.

Acute effects of hypercholesterolemic diet on erectile responses in rats.

OBJECTIVE: The aim of this study was to evaluate the acute effects of a high cholesterol diet (HCD) on erectile and endothelial functions in Sprague-Dawley rats. MATERIALS AND METHODS: Sprague-Dawley rats were divided into 2 groups as control and HCD groups. The control group was fed on a normal diet and the hypercholesterolemia group was fed a 1% cholesterol-enriched diet daily for 2 weeks. Total cholesterol levels were measured at the end of 2 weeks in both groups. To examine the effect of HCD on erectile function, electric cavernous nerve stimulation (CNS) at 20 Hz with a pulse duration of 1 ms for 1 min at 5 V was performed. During CNS, we measured intracavernous pressure (ICP), mean arterial pressure (MAP), detumescence time and area under the curve (AUC). To evaluate the endothelial responses, acetylcholine (Ach) was applied cumulatively (1 nM to 1 microM) to thoracic aorta tissues contracted with 60 mM KCl. RESULTS: In the HCD group total cholesterol levels were significantly higher than in the control group (148.1 +/- 18.9 vs. 55.7 +/- 8.1 mg/dl, p = 0.002). The detumescence time was significantly decreased after HCD compared to the control diet (19.3 +/- 3.6 vs. 78.6 +/- 12.8 s, p < 0.001). The decreases in the HCD group were also significant in terms of ICP (53.4 +/- 4.5 vs. 35.6 +/- 5.5 mm Hg; p < 0.05), ICP/MAP (55.9 +/- 3.9 vs. 38.2 +/- 5.2%; p < 0.05) and AUC (1,404 +/- 197.1 vs. 2,250 +/- 253.7, p < 0.05) values. There were no significant changes in maximum relaxation responses of the thoracic aorta to Ach. CONCLUSION: These results suggest that erectile functions were significantly damaged early in HCD rats. However, endothelial functions, evaluated in the thoracic aorta, were not affected simultaneously with erectile functions in rats fed a low concentration of HCD.

An experimental approach to the interrelationship between hyperthyroidism and ejaculation latency time in male rats.

PURPOSE: We investigated the effects of experimentally induced hyperthyroidism on seminal vesicle pressure measurements and bulbospongiosus muscle contractile activity in a para-chloroamphetamine (Sigma-Aldrich) induced ejaculation model in rats. MATERIALS AND METHODS: Male Wistar rats were used in the study. Daily injection of 25 microg/100 gm body weight L-thyroxine (T4, Sigma-Aldrich) for 14 days was performed in 14 rats to induce hyperthyroidism. Seven L-thyroxine injected rats were in the hyperthyroid group. The remaining 7 rats (recovery group) underwent operation after a 28-day washout period to determine spontaneous recovery from hyperthyroidism. At each operation seminal vesicle catheterization was done to measure intraluminal pressure and bulbospongiosus muscle dissection was performed for electromyography. After intraperitoneal administration of 5 mg/kg para-chloroamphetamine physiological parameters related to the ejaculatory process were measured. RESULTS: The interval between para-chloroamphetamine administration and first ejaculation was significantly decreased in the hyperthyroid rat group compared with that in the control group (mean +/- SD 202.8 +/- 22.3 vs 465.4 +/- 104.6 seconds, p = 0.001). Seminal vesicle phasic contraction frequency was significantly higher than control group values in hyperthyroid rats (for 30 minutes 32.3 +/- 13.9, p = 0.047). The mean AUC of bulbospongiosus muscle electromyography activity was also significantly increased in this group (11.1 +/- 4.1 V per second x 10(-4), p = 0.0001). All parameters in recovery and control group rats were not significantly differed from each other. CONCLUSIONS: Hyperthyroidism leads to enhanced seminal vesicle contraction frequency and bulbospongiosus muscle contractile activity in rats. Hyperthyroidism affects the emission and expulsion phases of ejaculation in reversible fashion.

Contractility of diabetic human corpus cavernosum smooth muscle in response to serotonin mediated via Rho-kinase.

BACKGROUND/AIMS: Serotonin (5-hydroxytryptamine, 5-HT)-induced contraction and the involvement of RhoA/Rho-kinase pathway in the 5-HT-induced contraction was investigated isometrically in vitro in both diabetic and nondiabetic human corpus cavernosum (HCC) tissues. METHODS: HCC tissues were obtained from 12 patients. The response to 5-HT (10(-9) to 10(-5) mol/l) was studied in isolated HCC tissues in the absence and in the presence of a Rho-kinase inhibitor (Y-27632). RESULTS: Preincubation with Y-27632 attenuated maximum contractions induced by 5-HT in tissues of both nondiabetics and diabetics. When diabetic and nondiabetic groups were compared, no significant difference was seen in 5-HT-induced contraction alone, but in the presence of Y-27632, 5-HT-induced contraction was significantly higher in the diabetic group. CONCLUSION: These results suggest that the Rho-kinase-mediated pathway plays an important role for 5-HT-induced contraction in diabetic corpus cavernosum tissues.

Restraint stress impairs erectile responses in rats.

It has been established that various forms of physical and psychological stress reduce sexual functions. However, there is no study yet evaluating the functional changes over cavernosal pressure in rats exposed to restraint stress. In this study, we aimed to investigate the convenience of the restraint stress model that may be used to determine the disruptive effects of stress on erectile function. Sprague Dawley rats were randomized into two groups as control (n = 7) and stress (n = 7) groups. In the stress group, rats were placed for 60 minutes in a cylindrical plastic tube with holes for fresh air supply (restraint stress). Following the stress application, several parameters for erectile responses were evaluated immediately. The control animals were maintained at room temperature without any procedure until the measurement. During the electrical stimulation of cavernous nerve, we measured the intracavernous pressure (ICP), the ratio of ICP to the mean arterial pressure (MAP), and detumescence time. There were significant decreases in ICP (24.4 +/- 4.1 vs 53.4 +/- 4.5 mmHg, p < 0.01), ICP/MAP (34.4 +/- 7.8% vs 55.7 +/- 3.9%, p < 0.05), and detumescence time (31.7 +/- 6.1 vs 78.6 +/- 12.8 sec, p < 0.01) in stress group when compared to control group. Thus, restraint stress declined detumescence time and decreased intracavernosal pressure in male rats. In conclusion, restraint stress model in rats may be useful for determining the effects of stress on erectile response. Even a short-term restraint stress may cause erectile dysfunction.

Effects of partial bladder outlet obstruction on contraction and relaxation response of rabbit corpus cavernosum.

It has been well established that erectile dysfunction (ED) is a common incident in patients with benign prostate hyperplasia. Animal models have been described to investigate the relationship between bladder obstruction and ED. In this study, we aimed to investigate whether partial bladder outlet obstruction (PBOO) induces changes in the contraction and relaxation response of corpus cavernosum smooth muscle (CCSM) of the penis in the rabbit model. Partial bladder obstruction was performed in rabbits as previously described. After 2 and 4 weeks of follow-up, control, sham-operated (2- and 4-week duration) and partial bladder outlet obstructed (obstruction of 2- and 4-week duration) rabbits were sacrificed and their bladder masses determined. Then CCSM tissue was obtained. Contraction responses induced by 124 mM KCl, phenylephrine (10(-6) to 10(-4)M) and relaxation responses induced by doxazosin (10(-7) to 10(-5)M) in CCSM of rabbits were determined. The obtained contraction and relaxation responses of all groups were compared. Bladder weight was significantly higher in PBOO groups than in control and sham-operated rabbits. Contraction responses induced by KCl and phenylephrine were statistically enhanced in the 4-week PBOO groups than controls. However, there was no statistically significant difference in any KCl, phenylephrine and doxazosin responses between 2- and 4-week sham-operated and PBOO groups. The rabbit model of PBOO described for the studies which examine bladder responses is useful for creating bladder outlet obstruction. However, this model is not suitable for the investigation of outlet obstruction-related ED.

The effect of nonsteroidal anti-inflammatory drugs on rat gastric mucosa. The role of endothelin.

OBJECTIVE: To investigate the role of endothelin on nonsteroidal anti-inflammatory drugs (NSAIDs) and selective cyclooxygenase-2 (COX2) enzyme inhibitors-induced effects on the gastric mucosa. METHODS: This study was carried out in the Department of Pharmacology Laboratory, Faculty of Medicine, Dokuz Eylul University, Izmir, Turkey during the period January to December 2002. In the first group a cyclooxygenase-1 (COX1) and COX2 enzyme inhibitor, indomethacin (25 mg/kg, subcutaneous injection (s.c), n=7), a selective COX2 enzyme inhibitor, NS398 (10 mg/kg, s.c) and normal saline were administered. In the second group, endothelin-1 (ET1) was administered (200 pmol/kg) alone, in the presence of an endothelin receptor antagonist bosentan, (100 mg/kg) and PGE1 [40 microg/kg, orally] with submucosal injection. In the third group, NS398 and indomethacin were applied in the presence of bosentan. In the fourth group, NS398 were applied in the presence of N (G)-nitro-l-arginine methyl ester (L-NAME) (10 mg/kg, s.c). RESULTS: Indomethacin caused gastric mucosal injury. The effect of NS398 on gastric mucosa did not differ considerably from that of the control group. Submucosal injection of ET1 caused a gastric damage, which could not be prevented by intragastric administration of bosentan, while pretreatment with PGE1 prevented ET1-induced ulcer. Pretreatment with bosentan did not attenuate indomethacin-induced gastric mucosal damage but it increased NS398-induced damage by 1.5 fold. Pretreatment with L-NAME increased NS398-induced gastric mucosal damage as bosentan did. CONCLUSION: These results suggest that neither endothelin-induced nor indomethacin-induced ulcer is completely receptor dependent. Cyclooxygenase-2 inhibitors caused ulcer in the presence of bosentan. Protective effects of gastric mucosal injury of COX2 inhibitors may be via endothelin receptor related nitric oxide release.

[Quantification of papain-induced rat osteoarthritis in relation to time with the Mankin score]. / Siçanlarda papainle olusturulan osteoartritin Mankin skoru ile zamana bagli derecelendirilmesi.

OBJECTIVES: The aim of this study was to evaluate structural changes in relation to time with the use of the Mankin scoring system in papain-induced rat osteoarthritis. METHODS: Osteoarthritis was induced in 21 male Wistar rats by injecting an admixture of 4% papain (10 microl) and its activator 0.03 M cycteine (10 microl) into the right knee joints on the first, fourth, and seventh days. The same volume of sterile saline solution was injected into the left knees as controls. The rats were assigned to three groups equal in number and were sacrificed under high-dose ether anesthesia after one, two, and four weeks of the last papain injection, respectively. The study and control knee joints were removed and histologic changes in cartilage structure were assessed and quantified with the modified Mankin scoring system. RESULTS: Histologically, all papain injected knees exhibited irregularity and fibrillation in the superficial layer, decreased cell count and multilayering in transitional and radial zones, and no pannus formation. The modified Mankin scores were significantly higher compared to the control knees in all the groups (p<0.05), being 4.3+/-0.9, 6.9+/-1.3, and 10.4+/-1.9 in diseased knees, and 2.7+/-0.5, 4.0+/-0.8, and 4.4+/-1.0 in the control knees after one, two, and four weeks of the last papain injection, respectively. There was a significant difference between the Mankin scores of the rats sacrificed after one and four weeks of the last papain injection (p=0.0471). CONCLUSION: Findings observed after four weeks of papain injection seem to be consistent with early osteoarthritic changes. Our results may provide insight into therapeutic strategies for early osteoarthritis.

The role of water-soluble meconium subfraction and lipid-soluble meconium subfraction on the superior mesenteric artery vasoconstriction in chick embryos.

OBJECTIVE: Intraamniotic meconium has been responsible for intestinal damage in gastroschisis and meconium-dependent intestinal ischemia has been proposed to induce additional intestinal damage in gastroschisis. This study is aimed to determine the effects of lipid and water-soluble meconium subfractions on the contractility of the superior mesenteric artery (SMA). MATERIALS AND METHODS: The study was conducted on 18-day fertilized chick embryos (Gallus Domesticus). Meconium is fractioned into water and lipid-soluble components. Only one SMA tissue was prepared from each embryo and suspended in the organ bath. Isometric contraction responses (ICR) were created in SMA tissues by one hour of incubation in Krebs-Henseleit solution for each group. Groups consisted of control, meconium, water-soluble meconium subfraction and lipid-soluble meconium subfraction. ICR of the SMA specimens were evaluated with a transducer-amplifier system on a computer. The data were expressed (mean±1SD) as milliNewton (mN). RESULTS: The ICR of the meconium, water-soluble meconium subfraction and lipid-soluble meconium subfraction groups were significantly high when compared to the control group (p<0.01). The meconium and water-soluble meconium subfraction created more contraction response than the lipid-soluble meconium subfraction (p<0.01). The ICR of the meconium group was not different from the ICR of the water-soluble meconium subfraction group (p>0.05). CONCLUSION: Water-soluble meconium subfraction has a profound vasoconstrictor effect on the SMA compared to the lipid-soluble meconium subfraction.

Correlation between Amitriptyline-Induced Cardiotoxic Effects and Cardiac S100b Protein in Isolated Rat Hearts.

BACKGROUND: Amitriptyline is an important cause of mortality due to its cardiovascular toxicity. AIMS: To investigate the changes in levels of cardiac S100b protein on amitriptyline-induced cardiotoxicity and also to examine the correlation between amitriptyline-induced cardiotoxic effects and cardiac S100b protein in an isolated rat heart model. STUDY DESIGN: Animal experimentation, isolated heart model. METHODS: After a stabilization period, isolated hearts were randomized to two groups (n=5 and n=7). In the control group, isolated hearts were subjected to an infusion of 5% dextrose for 60 minutes. In the amitriptyline group, 5.5×10-5 M amitriptyline was infused for 60 minutes to achieve amitriptyline toxicity. After the infusion period, heart tissues were removed for histological examination. RESULTS: In comparison to control treatment, amitriptyline infusion decreased left ventricular developed pressure (LVDP), dp/dtmax and heart rate (HR) and significantly prolonged QRS duration (p<0.05). The semiquantitative scores for S100b protein levels in amitriptyline-infused hearts were higher than in the control group (p<0.01). At the end of the experiment, in the amitriptyline-infused group, significant correlations were found between LVDP and S100b protein scores (r=-0.807, p=0.003) and between QRS duration and S100b protein scores (r=0.859, p=0.001). CONCLUSION: Our results indicate that the S100b protein may be a helpful indicator or biomarker in studying the cardiotoxic effects of amitriptyline.

Effects of resveratrol on the alterations of cavernosal eNOS and LOX-1 expression in the hypercholesterolemic condition: a preliminary study.

BACKGROUND/AIM: The aim of this study was to determine the effects of resveratrol on the alterations of cavernosal eNOS and LOX-1 mRNA expression in the hypercholesterolemic condition. MATERIALS AND METHODS: Twenty-one New Zealand white male rabbits were separated into three groups. Rabbits were fed with a normal dietary intake for the control group and a 2% cholesterol diet for the hypercholesterolemia and resveratrol groups for 6 weeks. Resveratrol 4 mg/kg daily was administered for the resveratrol group. Cavernosal LOX-1 and eNOS mRNA expressions were determined with real-time RT-PCR in all groups. The statistical analysis was performed with the Kruskal-Wallis and Mann-Whitney U tests. RESULTS: We found no difference between mean LOX-1 mRNA expression levels in the three groups. Lower mean eNOS mRNA expression level was determined in the hypercholesterolemia group when compared with the control group (P = 0.011). Mean eNOS mRNA expression level in the resveratrol group was similar to that in the control group but significantly higher than that in the hypercholesterolemia group (P < 0.001). CONCLUSION: This preliminary study demonstrates the beneficial effects of resveratrol on cavernosal eNOS expression. The presence of cavernosal LOX-1 expression was also shown for the first time. Resveratrol may be an alternative option in hypercholesterolemic erectile dysfunction with further studies supporting its beneficial effects on the corpus cavernosum.

Intra-amniotic administration of urinary trypsin inhibitor preserves intestinal contractility in meconium induced intestinal damage in chick embryos with gastroschisis.

BACKGROUND: Intestinal damage causes intestinal dysmotility in gastroschisis. Urinary trypsin inhibitor (UTI) has been shown to prevent intestinal damage in chick embryos with gastroschisis. The effect of intra-amniotic administration of UTI on intestinal motility in gastroschisis has not been investigated. METHODS: Five-day-old fertilized chick embryos were used. Gastroschisis was created through the amniotic cavity without opening the allantoic cavity. There were six groups; control, gastroschisis only, gastroschisis plus meconium and three treatment groups. In the treatment groups, 100 IU/mL, 200 IU/mL and 400 IU/mL UTI were instilled into the amniotic cavity of the gastroschisis plus meconium embryos, respectively. Serosal thickness of the intestines in each group was measured histopathologically. The contractions of the intestines were evaluated by in vitro organ bath technique and the responses were expressed as maximal contraction induced by acetylcholine. RESULTS: The serosal thickness was significantly increased in the gastroschisis plus meconium, 100 IU/mL, 200 IU/mL UTI groups compared to control and gastroschisis only groups. The serosal thickness of the 400 IU/mL UTI group was similar to control and gastroschisis only groups. Contractility of the intestines was diminished in the gastroschisis plus meconium, 100 IU/mL and 200 IU/mL UTI groups. There was no significant difference regarding contractility among control, gastroschisis only and 400 IU/mL UTI groups. CONCLUSION: Intra-amniotic administration of UTI preserves intestinal contractility in chick embryos with gastroschisis. However, preservation of intestinal dysmotility by using UTI in the human gastroschisis cases needs further experimental and clinical trials.

In vitro analysis of the effect of hyperbilirubinemia on rabbit ureter and bladder.

Spontaneous resolution of intrauterine pelvic dilatations after birth is an expected outcome. In nonobstructive pelvic dilatations, changes in ureteral and bladder physiology may also play a part. We aimed to demonstrate the effect of increased concentrations of bilirubin on ureteral and bladder muscles in vitro. Normal and pathologic concentrations of bilirubin (3.5x10(-7)-10(-5)M and 10(-4)-4x10(-4)M, respectively) caused no change in the basal ureter tension (343.9+/-29.4 mg). Normal concentrations of bilirubin caused no difference in basal bladder tension (430.2+/-70.2 mg), but pathologic concentrations caused a decrease of 303.8+/-52.9 mg. Normal and pathologic amounts of bilirubin were cumulatively applied to rabbit ureteral and bladder tissues both after reaching basal tension and when contracted with KCl (80 mM and 120 mM KCl for ureter and bladder, respectively). The cumulative addition of normal bilirubin concentrations to the ureteral tissues precontracted with KCl produced 86.4+/-7.2% relaxation, while the addition of pathologic bilirubin concentrations produced a relaxation of 133.9+/-17.4%, which was significantly higher (p=0.04). Similarly, the addition of normal concentrations of bilirubin to the bladder tissues precontracted with KCl produced a maximal relaxation of 35.3+/-2.2%, while pathologic concentrations produced a maximal relaxation of 53.5+/-3.5%, which was significantly higher (0.001). Consequently, high concentrations of bilirubin caused a mild relaxation in basal ureteral and bladder tensions, while pathologically increased concentrations led to significant relaxation in both types of precontracted tissues. We suggest that high bilirubin levels may partly but not directly contribute to the spontaneous recovery of hydronephrosis because of the relaxation effect on bladder while probably causing susceptibility to urinary tract infections because of relaxation of both ureteral and bladder tissues.

Effect of doxazosin with and without rho-kinase inhibitor on human corpus cavernosum smooth muscle in the presence of bladder outlet obstruction.

PURPOSE: We investigated the relationship of adrenergic responses in corpus cavernosum tissues in the presence of BOO using the alpha1-adrenergic receptor antagonist doxazosin (Pfizer, New York, New York) and the rho-kinase inhibitor Y-27632 (Calbiochem, San Diego, California). MATERIALS AND METHODS: CCSM tissue was obtained from patients who underwent penile prosthesis implantation. Patients were divided into 2 groups according to the presence of BOO. The submaximal (EC80) concentration of phenylephrine (Sigma Chemical Co., St. Louis, Missouri) was calculated by evaluating adrenergic activity responses with cumulatively applied phenylephrine. After achieving a stable contraction plateau test compounds were put in an organ bath. The relaxant potencies of doxazosin and Y-27632 were expressed as the percent of inhibition of the contraction plateau induced EC80 concentration of phenylephrine. Relaxation responses in the 2 groups were compared. RESULTS: At the highest dose of increasing concentrations phenylephrine generated 70% more contraction response in the BOO positive group than in the BOO negative group. Doxazosin and Y-27632 caused concentration dependent relaxation in CCSM precontracted by phenylephrine. With doxazosin significantly higher relaxation responses were attained in the BOO positive group in terms of log IC50 and the maximal relaxation response (p = 0.0353 and 0.0003, respectively). Maximum relaxation responses following Y-27632 administration were significantly higher in the BOO positive group. CONCLUSIONS: The contractility of human corpus cavernosum is increased in the presence of BOO. Doxazosin and Y-27632 generate effective CCSM relaxation in the presence of BOO. Doxazosin and Y-27632 may be the alternatives for the treatment of erectile dysfunction associated with BPH.

No beneficial effects of joint distraction on early microscopical changes in osteoarthrotic knees. A study in rabbits.

BACKGROUND: Although promising results have been reported, on the use of joint distraction in osteoarthrotic joints, the mechanism behind the effects has not yet been expland. MATERIAL AND METHODS: 24 rabbits were randomly divided into 4 groups and osteoarthrosis was induced by papain injection. The first group served as control and the others were treated by simple external fixation (group 2), articulated distraction (group 3) or nonarticulated distraction (group 4). RESULTS: Histologically, there was no significant difference between the first, the second and the third groups. However, osteoarthrosis increased in group 4. INTERPRETATION: We conclude that joint distraction has no beneficial effect on the osteoarthrotic cartilage in papain-induced osteoarthrosis, and nonarticulated distraction worsens the results.

The effect of the nitric oxide synthesis inhibitor L-NAME on amitriptyline-induced hypotension in rats.

OBJECTIVE: Hypotension induced by tricyclic antidepressants is multifactorial. Previous animal experiments suggest a contribution from nitric oxide production. Our study aimed to evaluate the role of nitric oxide in amitriptyline-induced hypotension using N-nitro-L-arginine methyl ester, a nitric oxide synthesis inhibitor, and 3-morpholino sydnonimine, a nitric oxide donor, in anesthetized rats. METHODS: Amitriptyline intoxication was induced by the continuous infusion of amitriptyline 0.625 mg/kg/min throughout the experiment in anesthetized rats. Fifteen and 25 minutes after amitriptyline infusion began, two bolus doses of 10 mg/kg of N-nitro-L-arginine methyl ester (n = 8) or an equivalent volume of 5% dextrose solution (n = 8) was administered to each rat (Protocol 1). To investigate whether the effect of N-nitro-L-arginine methyl ester on blood pressure is counteracted by 3-morpholino sydnonimine, after the same protocol of amitriptyline infusion and 5 minutes after an N-nitro-L-arginine methyl ester bolus, a bolus of 3000 nmol/kg of 3-morpholino sydnonimine was administered (n = 8) to each rat (Protocol 2). To investigate the effect of N-nitro-L-arginine methyl ester on 3-morpholino sydnonimine induced hypotension, a group of rats received a continuous infusion of 0.54 mg/kg/h of 3-morpholino sydnonimine until 50% reduction was observed in mean arterial blood pressure followed by a bolus dose of 10 mg/kg of N-nitro-L-arginine methyl ester (n = 6) or 5% dextrose solution (n = 6) (Protocol 3). Outcome measures included mean arterial blood pressure, heart rate, and QRS duration in electrocardiogram. Student's t test and survival analysis were used for selected comparisons. RESULTS: For all parameters, the treatment groups were similar at baseline and at postamitriptyline periods before therapy was rendered. Amitriptyline infusion significantly reduced mean arterial blood pressure by 50.8 +/- 2.2% and prolonged QRS by 23.9 +/- 7.2% after 15 minutes. In Protocol 1, N-nitro-L-arginine methyl ester significantly increased mean arterial blood pressure compared to dextrose-treated control animals within 30 minutes (77.9 +/- 8.5% vs. 49.7 +/- 5.0% mmHg, p < 0.01, 95% CI 57.1-98.7%). QRS duration progressively increased during the amitriptyline infusion; however, there was no significant difference in QRS width between N-nitro-L-arginine methyl ester and control groups at any time point. N-nitro-L-arginine methyl ester increased survival time compared to controls (33.4 +/- 4.1 vs. 19.9 +/- 2.7 minutes, p < 0.01, 95% CI 25.4-41.3) but did not affect mortality. In Protocol 2 of continuous infusion of amitriptyline, 3-morpholino sydnonimine counteracted the N-nitro-L-arginine methyl ester-induced increase in mean arterial blood pressure. In both protocols, heart rate decreased significantly during amitriptyline infusion but there was no difference between treatment and control groups. In Protocol 3, N-nitro-L-arginine methyl ester bolus reversed 3-morpholino sydnonimine-induced hypotension compared to dextrose bolus. (83.8 +/- 5.7% vs. 54.6 +/- 4.8%, p < 0.01, 95% CI 69.2-98.4). CONCLUSION: N-nitro-L-arginine methyl ester is found to be effective in temporarily improving hypotension and prolonging survival time but does not affect overall mortality. Because this effect was antagonized by 3-morpholino sydnonimine, nitric oxide production appears to contribute to the pathophysiology of amitriptyline-induced hypotension.