Gender and relaxation to C-type natriuretic peptide in porcine coronary arteries

Experiments were designed to determine whether or not relaxations of coronary arterial smooth muscle to C-type natriuretic peptide (CNP) vary according to gender, and if so, to determine mechanisms for the differences, Rings of coronary arteries without endothelium from sexually mature male and female Yorkshire pigs were suspended in organ chambers for measurement of isometric force. Cumulative concentration-responses to CNP (10^-9-10^-7 M) were obtained in the absence and presence of either K⁺ channel blockers (charybdotoxin, apamine, or glibenclamide, 10^-7 M) or the clearance- receptor antagonist C-ANP (10^-6 M) during contractions to prostaglandin F₂α (2 μM). Relaxations to CNP were significantly less in arteries from male compared with female pigs and were significantly attenuated by charybdotoxin and glibenclamide in both sexes. However, apamine reduced relaxations to CNP only in arteries from female pigs. C-ANP significantly potentiated relaxations to CNP only in arteries from male pigs. In separate experiments, cyclic guanosine monophosphate (cGMP) was measured by radioimmunoassay at specified times after the addition of CNP (10^-7 M). Peak increases in cGMP were greater and occurred earlier in arteries from female than from male pigs; these differences were eliminated by the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (10^-4 M). These results demonstrate three mechanisms that contribute to gender differences in CNP-mediated relaxation of coronary arterial smooth muscle: activation of low conductance Ca²⁺-activated K⁺ channels, natriuretic peptide clearance receptors, and activity/regulation of phosphodiesterases.