EFFECTS OF ATRIAL-NATRIURETIC-PEPTIDE AND CYCLIC GUANOSINE-MONOPHOSPHATE ON ISOLATED HUMAN MYOMETRIAL ARTERIES PRECONSTRICTED BY ENDOTHELIN-1

In the present in vitro study we investigated the possible vasorelaxing effect of atrial natriuretic peptide (ANP) and cyclic guanosine monophosphate (cGMP) on small intramyometrial arteries precontracted by endothelin-l (ET-1). Myometrial biopsies from normotensive pregnant women were obtained during cesarean section and arteries of resistance vessel size were dissected and mounted in a tissue chamber for isometric registration of contractile tone. In arteries preconstricted with ET-1 (10(-8) M), ANP produced a concentration-dependent relaxation of 19 +/- 5%(mean +/- SEM) and 27 +/- 7% at concentrations of 10(-7) and 3 x 10(-7) M, respectively. cGMP induced a relaxation of 13 +/- 2, 18 +/- 3, 25 +/- 4 and 30 +/- 7% at concentrations of 10(-5), 10(-4), 3 x 10(-4) and 10(-3) M, respectively. Pretreatment with ANP did not attenuate the contraction produced by ET-1. We suggest that ANP may have a vasodilating effect on preconstricted human uteroplacental vessels. It also provides evidence for the role of other endogenous or exogenous vasodilators acting via cGMP-dependent mechanisms in the counteraction of ET-1-induced contraction of the myometrial resistance vessels during pregnancy.