The relaxation induced by uroguanylin and the expression of natriuretic peptide receptors in human corpora cavernosa.

INTRODUCTION: Receptors for natriuretic peptides have been demonstrated as potential targets for the treatment of male erectile dysfunction. AIM: This study investigates the relaxant effects of the atrial natriuretic peptide (ANP) and uroguanylin (UGN), and expression of natriuretic peptide receptors on strips of human corpora cavernosa (HCC). MAIN OUTCOME MEASURES: Quantitative analysis of natriuretic receptor expression and relaxation of precontracted strips were used to assess the membrane-bound guanylate cyclase-cyclic guanosine monophosphate (cGMP) pathway in HCC strips. METHODS: HCC was obtained from a cadaver donor at the time of collection of organs for transplantation (14-47 years) and strips were mounted in organ baths for isometric studies. RESULTS: ANP and UGN both induced concentration-dependent relaxation on HCC strips with a maximal response attained at 300 nM, corresponding to 45.4±4.0% and 49±4.8%, respectively. The relaxation is not affected by 30 µM 1H-[1,2,4]oxaolodiazolo[4,3-a]quinoxalin-1-one (ODQ) (a soluble guanylate cyclase inhibitor), but it is significantly blocked by 10 µM isatin, a nonspecific particulate guanylate cyclase (pGC) inhibitor. UGN was unable to potentiate electrical field stimulation (EFS) or acetylcholine-induced relaxations. The potential role of pGC activation and cGMP generation in this effect is reinforced by the potentiation of this effect by phosphodiesterase-5 inhibitor vardenafil (55.0±7.5-UGN vs. 98.6±1.4%-UGN+vardenafil; P<0.05). The relaxant effect was also partially (37.6%) blocked by the combination iberitoxin-apamin but was insensitive to glybenclamide. The expression of guanylate cyclase receptors (GC-A, GC-B, GC-C) and the expression of the natriuretic peptide "clearance" receptor (NPR-C) were confirmed by real-time polymerase chain reaction. The exposure of HCC strips to ANP (1 µM) and UGN (10 µM) significantly increased cGMP, but not cyclic adenosine monophosphate (cAMP) levels. CONCLUSIONS: UGN relaxes HCC strips by a guanylate cyclase and K(ca)-channel-dependent mechanism. These findings obtained in HCC reveal that the natriuretic peptide receptors are potential targets for the development of new drugs for the treatment of erectile dysfunction.

Renal and vascular effects of the natriuretic peptide isolated from Crotalus durissus cascavella venom.

Crotalus durissus cascavella is a snake that is usually found in the scrublands of northeast Brazil. The components of its venom may have effects on the vascular and renal systems. Recently, a new bradykinin inhibitory peptide has been identified in the venom of the Crotalinae family. The aim of the present study was to investigate the renal and vascular effects of the natriuretic peptide isolated from the venom of Crotalus durissus cascavella (NP2_Casca). The chromatographic profile showed the fractionation of substances identified as convulxin, gyroxin, crotoxin and crotamine, as well as fractions V and VI. The electrophoretic profile of fraction V consisted of several bands ranging from approximately 6kDa to 13kDa, while fraction VI showed only two main electrophoretic bands with molecular weights of approximately 6 and 14kDa. Reverse-phase chromatography showed that NP2_Casca corresponds to about 18% of fraction VI and that this fraction is the main natriuretic peptide. NP2_Casca was compared to other natriuretic peptides from other sources of snake venom. All amino acid sequences that were compared showed a consensus region of XGCFGX, XLDRIX and XSGLGCX. The group treated with NP2_Casca showed an increase in perfusion pressure, renal vascular resistance, urinary flow and glomerular filtration rate. The percent of total and proximal tubular transport of sodium was reduced significantly after administration of the peptide. The mean arterial pressure showed a dose-dependent decrease after infusion of NP2_Casca, and an increase in nitrite production. In the aortic ring assay, NP2_Casca caused a relaxant effect in endothelium-intact thoracic aortic rings precontracted with phenylephrine in the presence and absence of isatin. NP2_Casca failed to relax the aortic rings precontracted with an isosmotic potassium Krebs-Henseleit solution. In conclusion, the natriuretic peptide isolated from Crotalus durissus cascavella venom produced renal and vascular effects. NP2_Casca reduced total and proximal sodium tubular transport, leading to an increase in sodium excretion, thereby demonstrating a diuretic action. A hypotensive effect was displayed in an arterial pressure assay, with an increase in nitrite production, suggesting a possible vasoactive action.