The effect of chronic nitric oxide inhibition on vascular reactivity and blood pressure in pregnant rats.

CONTEXT The exact mechanism involved in changes in blood pressure and peripheral vascular resistance during pregnancy is unknown. OBJECTIVE To evaluate the importance of endothelium-derived relaxing factor (EDRF) and its main component, nitric oxide, in blood pressure and vascular reactivity in pregnant rats. DESIGN Clinical trial in experimentation animals. SETTING University laboratory of Pharmacology. SAMPLE Female Wistar rats with normal blood pressure, weight (152 to 227 grams) and age (90 to 116 days). INTERVENTION The rats were divided in to four groups: pregnant rats treated with L-NAME (13 rats); pregnant control rats (8 rats); virgin rats treated with L-NAME (10 rats); virgin control rats (12 rats). The vascular preparations and caudal blood pressure were obtained at the end of pregnancy, or after the administration of L-NAME in virgin rats. MAIN MEASUREMENTS The caudal blood pressure and the vascular response to acetylcholine in pre-contracted aortic rings, both with and without endothelium, and the effect of nitric oxide inhibition, Nw-L-nitro-arginine methyl-ester (L-NAME), in pregnant and virgin rats. The L-NAME was administered in the drinking water over a 10-day period. RESULTS The blood pressure decreased in pregnancy. Aortic rings of pregnant rats were more sensitive to acetylcholine than those of virgin rats. After L-NAME treatment, the blood pressure increased and relaxation was blocked in both groups. The fetal-placental unit weight of the L-NAME group was lower than that of the control group. CONCLUSION Acetylcholine-induced vasorelaxation sensitivity was greater in pregnant rats and that blood pressure increased after L-NAME administration while the acetylcholine-induced vasorelaxation response was blocked.