Orchidectomy enhances the expression of endothelin-1 and ETB receptors in rat portal vein.

Functional studies have shown that orchidectomy increases the effects of phenylephrine on rat portal veins, but that it is completely prevented in the presence of both ETA and ETB receptor antagonists. Although it suggests the involvement of endothelin-1 (ET-1), the local production of this vasoactive peptide has not been directly quantified in portal veins. Therefore, the aim of the present study was to verify if orchidectomy increases the local expression of ET-1 as well as ETA and ETB receptors in the rat portal vein. Indeed, the genic expression of ET-1, ETA and ETB receptors in rat portal veins taken from control (CONT), orchidectomized (ORX) and ORX plus testosterone-replacement therapy (ORX + T) animals were determined by Real Time RT-PCR. The results showed that orchidectomy induced a significant increment in genic expression of ET-1 and ETB receptors in the rat portal veins, which was completely reversed by testosterone replacement treatment. In conclusion, the results suggest that orchidectomy increases the production of ET-1 in the rat portal vein and that, at least partially, it may be related to the previously reported elevation of responses to phenylephrine.

Orchidectomy enhances the effects of phenylephrine in rat isolated portal vein.

1. Orchidectomy results in long-term testosterone deprivation similar to that observed in male clinical pathologies, such as hypogonadism and age-related reductions in plasma testosterone concentrations. Although the vascular effects of these sorts of hormone deprivations are known in arteries, they have not been studied to the same extent in veins. 2. The aim of the present study was to determine the effect of orchidectomy, with or without subsequent testosterone replacement (started 23 days after orchidectomy; 10 mg/kg, i.m., testosterone propionate once every 5 days for 3 weeks), on responses of rat isolated portal veins and vena cavae to exogenous phenylephrine (PE). Isolated vessels were mounted in an organ bath and concentration-response curves constructed to PE (10(-10)-10(-4) mol/L), endothelin (ET; 10(-10)-10(-5) mol/L) and KCl (10(-2)-1.2 x 10(-1) mol/L; as a control). 3. Orchidectomy had no effect on contractile responses of either the portal vein or vena cava to KCl. However, orchidectomy enhanced the maximum response (R(max)) of the portal vein, but not the vena cava, to PE. Testosterone replacement had no effect on these responses. The effects of orchidectomy on the R(max) to PE in portal veins were not altered by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester (10(-4) mol/L) alone or combined with 10(-5) mol/L indomethacin (a non-selective cyclo-oxygenase inhibitor), but they were abolished following treatment of isolated vessels with the ET(A) and ET(B) receptor antagonists BQ-123 and BQ-788 (both at 10(-6) mol/L). Orchidectomy did not alter portal vein responses to the application of exogenous ET. 4. The results of the present study indicate that orchidectomy-induced decreases in plasma testosterone can increase the venoconstrictor effects of PE on the portal vein and that this effect involves activation of both ET(A) and ET(B) receptors by locally produced ET.

The possible involvement of hyperpolarizing mechanisms in histamine-induced relaxation of the rat portal vein.

The present study evaluated the effects of histamine 10(-2) M on longitudinal preparations of rat portal vein. It was observed that histamine 10(-2) M induced relaxation of rat portal vein preparations pre-contracted with phenylephrine 10(-4) M. On the other hand, no pharmacological effects were observed in preparations not pre-contracted. The observed histamine-induced relaxing effect was absent in preparations pre-contracted with KCl (120 mM) or in the presence of depolarizing nutritive solution. However, the histamine-induced relaxation was still present in the endothelium-removed preparations. The histamine-induced relaxation also was not prevented by astemizole (10(-6) M, 10(-5) M and 10(-4) M), cimetidine (10(-5) M, 10(-4) M and 10(-3) M) or thioperamide (10(-6) M, 10(-5) M and 10(-4) M), selective antagonists H(1), H(2) and H(3), respectively. The presence of L-NAME 10(-4) M or L-NAME 10(-4) M plus indomethacin 10(-5) M also did not prevent the histamine-induced relaxation observed in rat portal vein. Thus, the histamine-induced relaxation observed in rat portal vein appears to involve a non-endothelial hyperpolarizing mechanism independent of H(1), H(2) and H(3) receptors.

Acetylcholine-induced aortic relaxation studied in salbutamol treated rats.

It has been proposed that the acetylcholine (ACh)-induced relaxation of the rat aorta is entirely mediated by endothelium derived-nitric oxide (NO). However, some authors have reported that indomethacin pretreatment attenuates ACh-induced relaxation of rat aortic ring preparations. Moreover, it has also been suggested that cAMP accumulation may regulate either nitric oxide synthase (NOS) or cyclooxygenase (COX) expression in different tissues. Thus, in this in vitro study we have investigated the endothelial mechanisms involved in the ACh-induced relaxation of ring preparations of the rat thoracic aorta, as well as the influence chronic treatment with the selective beta(2)-agonist salbutamol had upon such mechanisms. Results of functional experiments show that N(G)-monomethyl-L-arginine (L-NMMA, 3 x 10(-4) M) considerably inhibited the ACh-induced relaxation of rat aortic ring preparations. However, indomethacin (10(-5) M) was also found to partially attenuate this ACh response, suggesting that although NO is the most important mediator of the ACh-induced relaxation of the rat aortic ring preparations, vasorelaxation may also involve prostanoids. Moreover, the results suggest that treatment with salbutamol failed to produce any change in the ACh-induced relaxation of rat aortic ring preparations.

Phenylephrine-induced vasoconstriction of the rat superior mesenteric artery is decreased after repeated swimming.

This study was performed to determine the effect of forced swimming on the vascular responsiveness of the rat superior mesenteric artery to phenylephrine, focusing on the involvement of locally produced substances. Repeated but not single sessions of forced swimming exercise reduced the vasoconstrictor potency of phenylephrine in the studied arteries, regardless of the presence of intact endothelium. No significant changes were observed in the maximal response to phenylephrine. Treatment with indomethacin (1 microM) did not affect the exercise-induced reduction in vascular responsiveness to phenylephrine. However, the reduction of vascular reactivity to phenylephrine due to repeated exercise was no longer observed after treatment with N(G)-monomethyl-L-arginine (L-NMMA, 100 microM). The results suggest that repeated exercise reduces vasomotor responses to phenylephrine in rat superior mesenteric arteries through a non-endothelial nitric oxide (NO)-related mechanism.

Pharmacological evidence that methylene blue inhibits noradrenaline neuronal uptake in the rat vas deferens.

We report that the classical guanylate cyclase inhibitor methylene blue (MB, 1 microM or 10 microM), but not the selective guanylate cyclase inhibitor 1H-[1,2,4]oxidazolo[4,3-a]quinoxalin-1-one (1 microM) or nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (100 microM), causes a shift to the left in the concentration-response curve for noradrenaline in the isolated rat vas deferens preparations. The main objective of our study was to investigate the pharmacological mechanism by which MB increases the sensitivity of the rat vas deferens to noradrenaline. According to the presented results, MB did not change rat vas deferens sensitivity to methoxamine or noradrenaline in the presence of desipramine (0.1 microM). The pre-contracted rat vas deferens relaxation induced by isoproterenol was also not significantly changed by MB (1 microM). Thus, we suggest that MB increases rat vas deferens sensitivity through neuronal uptake inhibition without interfering in either the nitrergic mechanism or guanylate cyclase activity.