Oral Contraceptives and Responsiveness of Plasma Renin Activity and Blood Pressure in Normotensive Women

In young normotensive women (5 without and 5 with chronic oral contraceptives (= o.c.) cardiovascular homeostasis was challenged by isoproterenol and ergometer exercise, at normal and at resitricted sodium intake. Blood pressure and plasma renin activity (= PRA) did not differ between the 2 groups. Plasma renin substrate was markedly elevated in the o.c. group. Sodium restriction induced similar changes in body weight, urinary sodium excretion, systolic blood pressure and PRA; diastolic blood pressure decreased only in the non-o.c. group (by 6 mm Hg). In both groups isoproterenol and exercise induced similar changes in heart rate and blood pressure, except that after sodium restriction both stimuli caused larger decreases in diastolic blood pressure in the o.c. group. At both levels of sodium intake, PRA increased slightly less during exercise in the o.c. group; following restriction PRA response to isoproterenol was significantly less in the o.c. group. These results indicate that following chronic use of o.c. PRA responsiveness is normal or somewhat blunted. The different responses of diastolic blood pressure to sodium restriction and subsequent isoproterenol or exercise point to subtle changes in the inter-action of aodium and pressor mechanisms during chronic o.c. use.