The role of adenosine receptors on amitriptyline-induced electrophysiological changes on rat atrium.

We investigated the role of adenosine receptors in amitriptyline-induced cardiac action potential (AP) changes in isolated rat atria. In the first group, APs were recorded after cumulative addition of amitriptyline (1 µM, 10 µM and 50 µM). In other groups, each atrium was incubated with selective adenosine A(1) antagonist (8-cyclopentyl-1,3-dipropylxanthine (DPCPX), 10(-4) M) or selective adenosine A(2a) receptor antagonist (8-(3-chlorostyryl) caffeine, 10(-5) M) before amitriptyline administration. Resting membrane potential, AP amplitude (APA), AP duration at 50% and 80% of repolarization (APD(50) and APD(80), respectively), and the maximum rise and decay slopes of AP were recorded. Amitriptyline (50 µM) prolonged the APD(50) and APD(80) (p < 0.001) and the maximum rise slope of AP was reduced by amitriptyline (p < 0.0001). Amitriptyline reduced maximum decay slope of AP only at 50 µM (p < 0.01). DPCPX significantly decreased the 50-µM amitriptyline-induced APD(50) and APD(80) prolongation (p < 0.001). DPCPX significantly prevented the effects of amitriptyline (1 µM and 50 µM) on maximum rise slope of AP (p < 0.05). DPCPX significantly prevented the amitriptyline-induced (50 µM) reduction in maximum decay slope of AP (p < 0.001). The selective adenosine A(1) receptor antagonist prevented the electrophysiological effects of amitriptyline on atrial AP. A(1) receptor stimulation may be responsible for the cardiovascular toxic effects produced by amitriptyline.

The diuretic effect of urea analog dimethylthiourea in female Wistar rats.

Urea plays an important role in the urinary concentrating mechanism in the kidney by contributing greatly in the generation of hyperosmolar medulla due to the presence of urea transporters, which mediate facilitated transport of urea. In this study, we investigated the possible diuretic effect of urea analog and urea transporter inhibitor, dimethylthiourea (DMTU), in rats. Female Wistar rats were divided into two groups, group 1 (control group, n = 7) rats were injected with saline intraperitoneally (i.p.), while group 2 (DMTU group, n = 7) rats were injected with 500 mg/kg DMTU (i.p.) and an additional dose of 125 mg/kg DMTU after 8 h. DMTU administration induced an approximately three times increase in daily urine volume (p < 0.001) and decreased urine osmolality to approximately 35% of controls (p < 0.0001). DMTU also increased free water clearance (p < 0.0001) without a significant change in osmolar clearance. DMTU treatment caused an increase in urea clearance (p < 0.05) and fractional excretion of urea (p < 0.05) with a decrease in serum urea concentration (p < 0.001). DMTU had no effect on creatinine clearance or serum electrolytes, creatinine levels and osmolality. With these findings, we report for the first time that DMTU has a prominent diuretic effect with increased urea excretion, which may be explained by the inhibitory effect of the drug on urea transporters. Our findings suggest that DMTU may be used as a diuretic agent and also could be used as a lead compound for the development of novel diuretics.

Exercise and suspension hypokinesia-induced alterations in mechanical properties of rat fast and slow-twitch skeletal muscles.

Physical activity has a modulatory role on regulatory steps of excitation-contraction coupling (ECC) determining skeletal muscle contractility. We evaluated and compared the contractile responsiveness and caffeine-induced contractures of fast (extensor digitorum longus; EDL) and slow-twitch (soleus; SOL) muscles in suspension hypokinesia (SH) and exercised rats. After SH or low intensity exercise, EDL and SOL were isolated, twitch and tetanic contractions and caffeine (10 mM) contractures were recorded. Twitch and tetanic contractions of EDL increased by 60% in exercised rats (p <0.05) while no alteration was observed after SH. Exercise did not alter twitch and tetanic contractions of SOL, while SH depressed contractions (p <0.05). Caffeine contractures were diminished in exercised rat EDL (P <0.05). In SH-rat EDL, contractures increased in amplitude (p <0.01) with a rapid time course (p <0.05). Contractures did not change in SOL after exercise or SH. We concluded that SH and exercise exerted diverse modulatory effects on skeletal muscle contractility. Contractile improvement due to exercise was prominent in EDL. Our results suggest that the muscle-type specific adaptations are related to a change in ECC due to the differences in the regulatory steps, particularly in the intracellular Ca(2+) handling mechanisms.

Anti-androgen induced inhibition of testicular descent is associated with a decrease in sympathetic tonus.

BACKGROUND/AIMS: Responses of cremaster muscles and sacs from boys with undescended testis suggested less exposure against sympathetic, but more exposure against parasympathetic tonuses. Since the sympathetic tonus is androgen dependent, it has been suggested that androgens control the descent by influencing the sympathetic tonus. Therefore an experimental study was planned to evaluate the contractile responses of cremaster muscles according to locations of associated testes in rats subjected to intrauterine steroidal or non-steroidal anti-androgen exposure. METHODS: Time-mated pregnancies were started in 18 rats. They were divided into three groups and each group was given physiologic saline, flutamide or cyproterone acetate (Androcur Depot). Flutamide was administered from day 15 to day 19, cyproterone acetate on day 15 of intra-uterine life. At twelve weeks of age the localization of testes was evaluated, cremaster muscles were removed, and contractile properties were studied. Twitch and tetanic contractions were recorded isometrically at 37 degrees C. Effects of verapamil and isoprenaline were investigated. Results were compared by ANOVA and p values less than 0.05 were considered significant. RESULTS: Both testes of all available male offspring in the saline (n = 22) and cyproterone acetate-treated (n = 19) groups were in the scrotum. Sixty percent of males in the flutamide-treated group (n = 20) had undescended testes. Cremaster muscles of rats exposed to flutamide had a lower sensitivity to voltage sensitive Ca+2 channel blockade by verapamil (3 x 10(-4) mol/L, p < 0.05) and displayed greater contractile response to isoprenaline (10(-5) mol/L, p < 0.05). Alterations in contractile properties of the muscles did not differ according to localization of testes in rats subjected to flutamide exposure. CONCLUSIONS: CM in rats subjected to non-steroidal anti-androgen exposure revealed alterations that indicate a decrease in sympathetic tonus. Since non-steroidal anti-androgen also inhibits the descent, the present study provides experimental support for the involvement of sympathetic tonus in the androgenic control of testicular descent.

Evaluation of pelvic contractility in ureteropelvic junction obstruction: an experimental study.

BACKGROUND/PURPOSE: Ureteropelvic junction (UPJ) obstruction causes adaptive and/or compensatory alterations in renal pelvic contractility. As these alterations directly affect the outcome after renal damage, definition of these alterations is of the utmost importance from a clinical point of view. Thus, an experimental study was designed to determine the alterations of renal pelvic contractility in response to partial and complete UPJ obstruction. METHODS: Fifteen adult female New Zealand white rabbits were randomly assigned into three groups (each containing 5 rabbits) according to the degree of unilateral UPJ obstruction. Group I: sham operation was performed and served as the control group; group II: partial UPJ obstruction was made; group III: complete UPJ obstruction was made. The animals in groups I and II were sacrificed after three weeks and the rabbits in group III were sacrificed after two weeks. Muscle strips from the renal pelvis were prepared. Spontaneous mechanical activity and contractile responses to phenylephrine (PE), serotonin (5-HT), and KCl were recorded isometrically and compared in all groups. RESULTS: Both the frequency and amplitude of spontaneous mechanical contractions were significantly (p < 0.05) increased in partial (group II) and complete UPJ obstruction (group III) groups. PE and 5-HT-induced tonic contractions, which were more prominent in the complete and partial obstruction groups when compared with the control group (p < 0.05). PE and 5-HT also increased the frequency of spontaneous contractions in both partial and complete obstruction groups. KCl induced long lasting tonic contractions in the control muscles. The duration of contraction to reach the maximum amplitude was shortened in the obstruction groups and the amplitudes of the contractions were significantly augmented when compared to control preparations. CONCLUSION: UPJ obstruction alters the contractile properties of renal pelvis smooth muscle. Increased frequency of spontaneous mechanical activity suggests that pacemaker cells of the renal pelvis change their activities in response to UPJ obstruction. Increase in tonic contraction amplitudes in response to PE and 5-HT suggests an increased sensitivity of smooth muscle cells to these agents. Potentiation of the contractile response to KCl suggests that adaptive changes take place at the level of excitation-contraction coupling in the smooth muscle of the renal pelvis following UPJ obstruction.

Mechanisms involved in contractile differences among cremaster muscles according to localization of testis.

BACKGROUND/PURPOSE: Evidence suggests differences in contractility in cremaster muscles (CM) associated with undescended testis caused by alterations of autonomic innervation. Contractile responses of CM to various pharmacologic agents were evaluated and compared according to the localization of testis. METHODS: Samples of CM from boys with undescended testis or inguinal hernia were obtained. Twitch and tetanic contractions were recorded isometrically at 37 degrees C. Effects of verapamil, isoprenaline, calcitonin gene-related peptide (CGRP), substance P (SP) and N(omega)-nitro-L-arginine (L-NNA) were investigated. Results were compared through 2-way analysis of variance, and P values less than.05 were considered to be different. RESULTS: Verapamil alone significantly (P <.05) decreased contraction amplitudes in CM from both sources; the decrease was more pronounced in CM from boys with inguinal hernia (P <.05). Although isoprenaline increased contraction amplitudes in CM associated with undescended testis (P <.05), CGRP and SP increased contraction amplitudes in CM associated with descended testis (P <.05). L-NNA increased contraction amplitudes in both groups (P <.05). The decrease of contraction amplitudes after verapamil displayed a similar pattern after isoprenaline, SP, and L-NNA. Verapamil-induced contractility decrease was more pronounced after CGRP in both groups (P <.05). CONCLUSIONS: Sensitivity of CM to verapamil differs according to localization of testis. Isoprenaline enhances contractility by stimulating Na(+)-K(+)ATPase in undescended testis without altering voltage-sensitive channel sensitivity to verapamil. CGRP and SP increase contractility in inguinal hernia, and CGRP increases the sensitivity of voltage-sensitive Ca(2+) channels to verapamil in CM from both groups. Nitric Oxide (NO) exerts inhibitory action on CM contractility, and it is less pronounced in undescended testis. These differences may contribute to pathophysiology of undescended testis.

Increased intra-abdominal pressure alters the contractile properties of rabbit bladder.

OBJECTIVE: To evaluate the effects of increased intra-abdominal pressure (IAP) on the contractility of the rabbit bladder, as the dynamics of the bladder may be impaired in conditions associated with a high IAP, e.g. constipation and pregnancy. Material and methods The study comprised 22 adult male New Zealand rabbits; six served as the control group, eight had an IAP of 7 cmH2O imposed for 10 days by instilling air into the abdominal cavity and this IAP was maintained for 60 days in a further eight rabbits. After treatment, the rabbits were killed, and the bladders removed and cut into 3 x 12 mm strips. The contractile activity of the muscle strips was then recorded isometrically. Electrical field stimulation (EFS) was applied using a pair of platinum ring electrodes in trains of 3 s duration every 100 s (1 ms, 100 V, 2-100 Hz). Contractile responses to carbachol and isotonic KCl were also evaluated. RESULTS: EFS induced a frequency-dependent increase in contractile activity in all bladder strips. Ten days of high IAP resulted in an increased responsiveness to EFS, but high IAP for 60 days reduced the EFS-induced responses to the control levels. Carbachol (10-9-10-3 mol/L) elicited concentration-dependent contractions in all groups. From the concentration-response curves of carbachol, the log EC50 values (the concentration producing half the maximum effect) of the control and 60-day treated animals were comparable, at -6.24 (0.05) and -6.25 (0.04), respectively. However, the log EC50 of the 10 day-treated group was -4.97 (0.08) and significantly (P < 0.01) lower than that of both groups. Isotonic KCl produced contractions in all preparations; these contractions in the control and 60-day treated animals were similar, while the 10 day-treated group had significantly (P < 0.05) higher contraction amplitudes. CONCLUSION: Increased IAP alters the contractile properties of the bladder and its responsiveness to carbachol and KCl. As the intravesical pressure closely reflects the IAP, both should be increased in the present experimental design.

Lack of carbachol response indicates the absence of cholinergic receptors in sacs associated with undescended testis.

BACKGROUND/PURPOSE: The mechanism of testicular descent remains controversial. The processus vaginalis (PV) contains smooth muscle and should have contractile activity that may contribute to descent. This study was designed to evaluate the smooth muscle of PVs associated with incomplete obliteration for spontaneous activities and responses to various stimuli, to determine if differences exist according to sex, diagnostic source, or location of the testis. MATERIALS: Peritoneal samples (n = 4); sacs from girls (n = 8) and boys with inguinal hernia (n = 12); and sacs from boys with hydrocele (n = 3), hydrocele of the cord (n = 2), or undescended testis (n = 7) were used for the current study. Tissues were attached to the isometric force displacement transducer in an organ bath containing mammalian Ringer's solution at 37 degrees C. Spontaneous mechanical activity and contractile responses of tissues to the electrical field stimulation, phenylephrine, carbachol, and serotonin were recorded. The values obtained from boys and girls with inguinal hernia and from boys with either undescended or descended testis were compared through Fisher's Exact test. RESULTS: There were no statistically significant differences in patient age between groups. Among the parameters studied, only the carbachol response of the sacs associated with undescended testis showed a significant difference compared with the others (P = .001). None of the sacs associated with undescended testis responded to carbachol, whereas all of the sacs from boys and girls with inguinal hernia responded to carbachol. CONCLUSIONS: Lack of carbachol response suggests the absence of cholinergic receptors within the sacs associated with undescended testis. The lack of cholinergic receptors may play a role in the failure of the process of testicular descent by hindering either PV elongation into the scrotum or a possible propulsive activity of the PV on the testis.