Alteration by oral contraceptives of normal menstrual changes in plasma renin activity, concentration and substrate.

Abstract

To access an oral contraceptives effect upon normal menstrual changes in plasma renin activity concentration and substrate normal menstruating women were assayed for plasma renin activity concentration and substrate before and while taking oral contraceptives. Determinations were made during midcycle at the luteal phase and after the completion of bleeding. Studies had previously shown that plasma renin activity was dependent upon the concentrations of both the enzyme and the substrate when reactions proceeded under in vivo conditions. During a normal menstrual cycle a rise in plasma renin activity occurred during the luteal phase due to an increase in plasma renin concentration without change in the renin substrate. Oral contraceptives induced a further rise in renin activity (P<.01) and renin concentration (P<.001) with no change in renin substrate. This increase in activity was also associated with a drop in plasma renin concentration suggesting decreased renin secretion from the kidney. An hypothesis was advanced that suppressed renin secretion was a normal response to elevated substrate levels and that inadequate suppression might account for the hypertensive effect of oral contraceptives. In 2 out of 6 hypertensive women taking oral contraceptives in this study this factor was felt to be the cause for the condition.