Cristina Domenech

Inhibition of neuroeffector transmission in human vas deferens by sildenafil.

Sildenafil (0.1–30 μM), a cyclic GMP phosphodiesterase 5 (PDE 5) inhibitor, induced inhibition of electrically evoked contractions of ring segments of human vas deferens from 34 vasectomies. Zaprinast (0.1–100 μM), another PDE 5 inhibitor, and the nitric oxide (NO) donor sodium nitroprusside (SNP) (0.1–100 μM) had no effect on neurogenic contractions. The inhibition induced by sildenafil was not modified by the inhibitor of guanylate cyclase 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxaline‐1‐one (ODQ) (1–30 μM) but it was abolished by the K+ channel blockers tetraethylammonium (TEA, 1 mM), iberiotoxin (0.1 μM) and charybdotoxin (0.1 μM). Sildenafil, zaprinast and SNP did not affect the contractions induced by noradrenaline. SNP (10 μM) caused elevation of cyclic GMP levels that was potentiated by sildenafil (10 μM) and zaprinast (100 μM). ODQ (10 μM) inhibited the increase in cyclic GMP. Sildenafil inhibits adrenergic neurotransmission in human vas deferens. The inhibition is not related to accumulation of cyclic GMP but is probably due to activation of prejunctional large‐conductance Ca2+‐activated K+ channels.

Effects of sildenafil on human penile blood vessels.

OBJECTIVES To investigate the effects of sildenafil on human penile blood vessels and evaluate the interaction of sildenafil with neurogenic-mediated responses. Sildenafil is currently used in the treatment of erectile dysfunction. METHODS Penile dorsal arteries and deep dorsal veins were obtained from 14 multiorgan donors. Vascular rings were suspended in organ bath chambers, and the isometric tension was recorded. We then studied the effects of sildenafil on precontracted vessels and the neurogenic (noradrenergic and nitrergic) responses. RESULTS Sildenafil (10(-9) to 3 x 10(-6) M) caused concentration-dependent relaxation and amplified the relaxation induced by sodium nitroprusside. Relaxation was unaffected by the inhibitor of nitric oxide synthase N(G)-monomethyl-L-arginine (10(-4) M). Compared with zaprinast, sildenafil was 8 to 10 times more potent in terms of the median effective concentration (EC(50)) values. Electrical field stimulation of the vessels under resting tension caused frequency-dependent contractions that were attenuated in the presence of sildenafil. When penile vessels were contracted after blockade of norepinephrine release with guanethidine (10(-6) M), electrical stimulation induced frequency-dependent, nitric oxide-dependent relaxations that were enhanced by sildenafil. CONCLUSIONS These results indicate that the relaxation of human penile arteries and veins induced by sildenafil involves inhibition of noradrenergic contraction, enhancement of neurogenic nitric oxide-mediated relaxation, and inhibition of smooth muscle contraction.

Inhibition of nitric oxide activity by arginine analogs in human renal arteries

BACKGROUND Plasma levels of endogenous guanidine compounds are increased in various pathologic conditions, including chronic renal failure. In the present study we tested the effects of some of these compounds on basal and stimulated nitric oxide activity in human renal arteries. METHODS Rings from human renal arteries were obtained from 22 patients undergoing nephrectomy. The rings were suspended in organ baths for isometric recording of tension. We then studied the effects of N(G)-monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (asymmetrical dimethylarginine [ADMA]), aminoguanidine (AG), and methylguanidine (MG) on artery rings under basal and stimulated conditions. RESULTS In precontracted arteries, L-NMMA (1 micromol/L to 1 mmol/L) and ADMA (1 micromol/L to 3 mmol/L) caused concentration- and endothelium-dependent contractions (median effective concentrations [EC50] = 13.3 micromol/L and 17.5 micromol/L, respectively; Emax = 15+/-4% and 17+/-4% of the response to 100 mmol/L KCl, respectively). Aminoguanidine (0.01 to 3 mmol/L) and MG (0.01 to 3 mmol/L) produced endothelium-independent contractions (Emax = 9+/-3% and 16+/-2% of the response to 100 mmol/L KCl, respectively). L-arginine (1 mmol/L) but not D-arginine (1 mmol/L) prevented the contractions by L-NMMA and ADMA, but did not change contractions induced by AG and MG. In precontracted arteries, the relaxation to acetylcholine was decreased but not abolished by L-NMMA and ADMA. The remaining relaxation was reduced by charybdotoxin (0.1 mol/L) and tetraethylammonium (1 mmol/L). CONCLUSIONS The results demonstrate that L-NMMA and ADMA reduce basal and stimulated nitric oxide activity in human renal arteries. An increase in the plasma concentrations of methylarginines associated with renal disease should be considered as a risk factor for endothelial dysfunction and abnormal vasomotor tone in human renal arteries.

Vasopressin receptors involved in adrenergic neurotransmission in the circular muscle of the human vas deferens

We studied the effects of vasopressin on the adrenergic responses of in vitro preparations of circular muscle from the vas deferens obtained from 28 men undergoing elective vasectomy. Vasopressin (3 x 10(-9)-3 x 10(-8) M) enhanced the phasic contractions elicited by electrical field stimulation and noradrenaline. This potentiation was blocked by the vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)vasopressin (10(-6) M) but not by the vasopressin V2 receptor antagonist [d(CH2)5, D-Ile2,Ile4,Arg8]vasopressin (10(-6) M). The Ca2+ antagonist nifedipine (10(-6) M) did not affect the potentiation of electrical field stimulation induced by vasopressin and noradrenaline but reduced KCl-induced contractions and abolished the induction of phasic activity by vasopressin in the presence of KCl. The results demonstrate that vasopressin, in addition to its direct contractile effects, strongly potentiates contractions of human vas deferens elicited by adrenergic stimulation. Both the direct and indirect effects of vasopressin appear to be mediated by vasopressin V1 receptor stimulation and are independent of Ca2+ entry through dihydropyridine Ca2+ channels.

Effects of antidepressants in adrenergic neurotransmission of human vas deferens.

OBJECTIVES To evaluate the effects of sertraline, fluoxetine, and amitriptyline on the contractile responses of the human vas deferens muscle elicited by norepinephrine, electrical field stimulation, and KCl, because the therapeutic action of antidepressants may be accompanied by sexual dysfunction related to the contractility of the vas deferens smooth muscle. METHODS Ring segments of the epididymal part of the vas deferens were taken from 32 elective vasectomies and mounted in organ baths for isometric recording of tension. We then studied the effects of sertraline, fluoxetine, and amitriptyline on the neurogenic and agonist-induced contractile responses. RESULTS Amitriptyline caused concentration-dependent inhibition of neurogenic and norepinephrine-induced contractions. In contrast, only the highest concentration (10(-5) M) of sertraline and fluoxetine reduced the adrenergic contractions. The dihydropyridine calcium antagonist nifedipine (10(-6) M) completely prevented the inhibitory effect of sertraline and fluoxetine on neurogenic and norepinephrine-induced contractions but did not change the inhibition caused by amitriptyline. Sertraline, fluoxetine, and amitriptyline (all at 10(-5) M) attenuated contractions elicited by KCl and reduced contractions induced by CaCl(2) in KCl-depolarized preparations. CONCLUSIONS The results indicate that sertraline and fluoxetine inhibit vas deferens motility through inhibition of Ca(2+) entry, with no effect on the adrenergic receptors, and amitriptyline acts as an adrenoceptor antagonist and inhibitor of the entry of calcium.

V2-receptor-mediated relaxation of human renal arteries in response to desmopressin.

The effects of deamino-8-D-arginine vasopressin (desmopressin), a V2 receptor antidiuretic agonist, were studied in isolated rings from branches of renal arteries obtained from 22 patients undergoing nephrectomy. The rings were suspended in organ bath chambers for isometric recording of tension. In precontracted rings with norepinephrine (10(-6) to 3 x 10(-6) mol/L), desmopressin (10(-11) to 3 x 10(-7) mol/L) caused endothelium-dependent relaxation (81%+/-4% reversal of the initial contraction in arteries with endothelium; 20%+/-4% in arteries without endothelium; P < .05). The relaxation to desmopressin in rings with endothelium was reduced significantly by indomethacin (10(-6) mol/L) and unaffected by the inhibitor of nitric oxide synthase NG-nitro-L-arginine methyl ester (10(-4) mol/L). Two V1 receptor antagonists (a peptidic and a nonpeptidic) had no effect on desmopressin-induced relaxation. However, V2 receptor antagonists (three peptidic and a nonpeptidic) reduced significantly (P < .05) the maximal response to desmopressin. The results of this study show that desmopressin exerts powerful endothelium-dependent relaxation of human renal arteries, probably through stimulation of V2-like receptors that may bring about the release of dilating prostaglandins.

Increased contraction to noradrenaline by vasopressin in human renal arteries.

Objective Arginine vasopressin (AVP) not only acts directly on blood vessels through vasopressin V1 receptor stimulation but also may modulate adrenergic-mediated responses in animal experiments. The aim of the present study was to assess whether subpressor concentrations of AVP could contribute to an abnormal adrenergic contractile response of human renal arteries. Methods Renal artery rings were obtained from 27 patients undergoing nephrectomy. The rings were suspended in organ bath chambers for isometric recording of tension. Results AVP (10−10 mol/l) and the vasopressin V1 receptor agonist [Phe2, Orn8]-vasotocin (10−10 mol/l) produced a leftward shift of the concentration–response curve to noradrenaline (half-maximal effective concentration decreased from 1.1 × 10−6 mol/l to 3.1 × 10−7 mol/l). The enhancement of noradrenaline-induced contractions was inhibited by the vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)AVP (10−8 mol/l) and unaffected by endothelium removal or pretreatment with the inhibitor of nitric oxide (NO) synthase NG-monomethyl-l-arginine (l-NMMA). The vasopressin V2 receptor agonist 1–desamino-8–D-arginine vasopressin (dDAVP) (10−10−10−8 mol/l) did not modify contractile responses to noradrenaline. In the presence of the dihydropyridine calcium antagonist nifedipine (10−6 mol/l), vasopressin failed to enhance the contractile response to noradrenaline. Conclusions The results demonstrate that subpressor concentrations of vasopressin potentiate the contractile effects of noradrenaline without intervention of the NO system. The effects appear to be mediated by vasopressin V1 receptor stimulation, which brings about an increase in calcium entry through dihydropyridine-sensitive calcium channels.

Neurogenic contraction and relaxation of human penile deep dorsal vein

The aim of the present study was to characterize neurogenic and pharmacological responses of human penile deep dorsal vein and to determine whether the responses are mediated by nitric oxide from neural or endothelial origin. Ring segments of human penile deep dorsal vein were obtained from 22 multiorgan donors during procurement of organs for transplantation. The rings were suspended in organ bath chambers for isometric recording of tension. We then studied the contractile and relaxant responses to electrical field stimulation and to vasoactive agents. Electrical field stimulation (0.5–2 Hz) and noradrenaline (3×10−10–3×10−5 M) caused frequency‐ and concentration‐dependent contractions that were of greater magnitude in veins denuded of endothelium. The inhibitor of nitric oxide synthesis NG‐nitro‐L‐arginine methyl ester hydrochloride (L‐NAME, 10−4 M) increased the adrenergic responses only in rings with endothelium. In preparations contracted with noradrenaline in the presence of guanethidine (10−6 M) and atropine (10−6 M), electrical stimulation induced frequency‐dependent relaxations. This neurogenic relaxation was prevented by L‐NAME, methylene blue (3×10−5 M) and tetrodotoxin (10−6 M), but was unaffected by removal of endothelium. Acetylcholine (10−8–3×10−5 M) and substance P (3×10−11–3×10−7 M) induced endothelium‐dependent relaxations. In contrast, sodium nitroprusside (10−9–3×10−5 M) and papaverine (10−8–3×10−5 M) caused endothelium‐independent relaxations. The results provide functional evidence that the human penile deep dorsal vein is an active component of the penile vascular resistance through the release of nitric oxide from both neural and endothelial origin. Dysfunction in any of these sources of nitric oxide should be considered in some forms of impotence.

Relaxation induced by milrinone and rolipram in human penile arteries and veins

We studied the relaxant effects of milrinone, an inhibitor of phosphodiesterase 3, and rolipram, an inhibitor of phosphodiesterase 4, on contracted human penile dorsal artery and deep dorsal vein. Vascular rings from 12 multi-organ donors were suspended in organ baths for isometric recording of tension. Both milrinone and rolipram inhibited (100%) the contraction induced by noradrenaline and shifted the relaxation-response curves to the cAMP forming agents prostaglandin E(1) and forskolin to the left. The findings indicate that the cAMP pathway appears to be a main determinant of relaxation in human penile vessels.