Juliana S. Baracat

Mechanisms underlying relaxation of rabbit aorta by bay 41-2272, a nitric oxide-independent soluble guanylate cyclase activator

1. The compound BAY 41‐2272 (5‐cyclopropyl‐2‐[1‐(2‐fluoro‐benzyl)‐1H‐pyrazolo[3,4‐b]pyridin‐3‐yl]‐pyrimidin‐4‐ylamine) has been described as a potent, nitric oxide (NO)‐independent, stimulator of soluble guanylate cyclase. In the present study, the mechanisms underlying the relaxant effect of BAY 41‐2272 in endothelium‐intact and ‐denuded precontracted rabbit aortic rings were investigated.

Nitric oxide release from human corpus cavernosum induced by a purified scorpion toxin.

OBJECTIVES To investigate the effects of a purified scorpion toxin (Ts3) on human corpus cavernosum (HCC) in vitro. Scorpion venoms cause a massive release of neurotransmitters that contribute to the clinical symptoms resulting from envenomation. METHODS HCC strips were mounted in organ baths containing Krebs solution. After equilibration, the tissues were precontracted with phenylephrine (10 micromol/L). The relaxations caused by Ts3 (30 nmol/L) were compared with those induced by electrical field stimulation (1 to 20 Hz) and nitric oxide (NO, 1 to 100 micromol/L). RESULTS The addition of Ts3 evoked long-lasting relaxations of precontracted HCC strips, and exogenously applied NO and electrical field stimulation caused short-lived responses. The NO synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME; 100 micromol/L) reduced by 87% +/- 2% the Ts3-induced relaxations; this inhibition was reversed by pretreating the tissues with L-arginine (1 mmol/L). The relaxant responses mediated by Ts3 were blocked to a similar degree by the soluble guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3,-alquinoxalin-1-one] (10 micromol/L). In contrast, the addition of the phosphodiesterase type 5 inhibitor sildenafil (0.1 micromol/L) significantly enhanced Ts3-evoked relaxations by 78% +/- 4%. The sodium channel blocker tetrodotoxin (1 micromol/L) completely blocked the relaxant responses elicited by both Ts3 and electrical field stimulation, without significantly affecting those elicited by NO. CONCLUSIONS The results indicate that Ts3 relaxes the HCC through the release of NO from nitrergic nerves. The elucidation of this mechanism is useful for the development of new therapeutic strategies to treat priapism after scorpion envenomation or to modulate sodium channel activity in the case of penile dysfunction.

Comparative Relaxing Effects of Sildenafil, Vardenafil, and Tadalafil in Human Corpus Cavernosum: Contribution of Endogenous Nitric Oxide Release

OBJECTIVES To compare the direct relaxant activity of sildenafil, vardenafil, and tadalafil in the human corpus cavernosum (HCC) and to investigate their modulatory effects on nitric oxide (NO)-mediated responses. Phosphodiesterase (PDE)-5 inhibitors cause cavernosal smooth muscle relaxation and penile erection. METHODS HCC strips were mounted in 10-mL organ baths containing Krebs solution and connected to force-displacement transducers. The changes in isometric force were recorded using the Powerlab 400 data acquisition system. Corporeal smooth muscle was precontracted submaximally with phenylephrine (10 micromol/L). RESULTS All PDE-5 inhibitors tested (0.001-10 micromol/L) relaxed phenylephrine-precontracted HCC with similar values of potency in a concentration-dependent manner. However, the maximal relaxations induced by tadalafil (83% +/- 4%) were significantly lower compared with sildenafil (107% +/- 5%) and vardenafil (111% +/- 3%). The NO synthesis inhibitor N-nitro-l-arginine methyl ester (100 micromol/L) caused significant rightward shifts in the concentration-response curves for sildenafil (4.0-fold), vardenafil (4.6-fold), and tadalafil (3.2-fold) in HCC tissue. The guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 micromol/L) also produced similar rightward shifts for these PDE-5 inhibitors. The cavernosal relaxations evoked by either acetylcholine or the NO donor glyceryl trinitrate were markedly potentiated by sildenafil, vardenafil, and tadalafil (0.1 micromol/L each). All PDE-5 inhibitors significantly increased the duration of electrical field stimulation-induced relaxations (8 Hz). CONCLUSIONS Our findings have shown that sildenafil, vardenafil, and tadalafil relax HCC tissues in a concentration-dependent manner, but the maximal relaxation obtained with tadalafil was significantly lower than that obtained with sildenafil and vardenafil. Moreover, the PDE-5 inhibitors interacted with endogenous and exogenous NO, amplifying its HCC relaxation.

Pharmacological characterization of the novel phosphodiesterase type 5 (PDE5) inhibitor lodenafil carbonate on human and rabbit corpus cavernosum

Methods In functional studies, cavernosal strips were mounted in organ baths for isometric force recording, coupled to a PowerLab 8/SPTM data acquisition system. Rats were surgically manipulated and telemetry transmitters were implanted in the abdominal aorta for measurements of systolic, diastolic and mean arterial blood pressure. For determination of PDE activity by LC-MS/MS analysis, lodenafilc arbonate (0.005–1 μM) was preincubated in the enzymatic mixture for 5 min at room temperature. Reaction was initiated by the addition of the substrate cGMP (5 μM) at 35°C for 30 min. Pharmacokinetics was studied by tandem mass spectrometry (LC-MS/MS) with positive ion electrospray ionization using multiple reactions monitoring (NMR) method. Blood samples were collected at 0.02 to 24 h after drug administration by intravenous (1 mg/kg) and oral (10 mg) routes. The hydrolysis of lodenafil carbonate (final concentration 10 μM) was also studied in human, dog and rat plasma as well as in acid solution (100 mM hydrochloric acid).

Run training ameliorates the established erectile dysfunction in rats under long-term nitric oxide (NO) blockade

Introduction Stimulation of nitrergic neurons and endothelial cells in the erectile tissue results in release of NO that diffuse to surrounding smooth muscle cells where it activates the soluble guanylate cyclase (sGC), facilitating the conversion of GTP to cGMP. This second messenger diminishes the intracellular levels of calcium thereby causing penile smooth muscle relaxation and penile erection [1]. Epidemiological studies have shown a strong association between erectile dysfunction (ED) and arterial hypertension [2], where the deficiency of the NO-cGMP pathway seems to greatly contribute to such association [3]. Regular physical exercise has been shown to increase the NO production thus ameliorating cardiovascular diseases [2,4]. Recently, we have shown that prior physical conditioning improves the erectile function in normotensive rats [5] and prevents the impaired corpus cavernosum relaxation secondary to chronic NO blockade in rats [2].