EFFECT OF ORAL CONTRACEPTIVES ON PERIPHERAL BLOOD FLOW IN UNTRAINED WOMEN AT REST AND DURING EXERCISE

Abstract

1993 Endothelium-derived nitric oxide is an important mediator of exercise-induced changes in skeletal muscle blood flow. Given the recently documented effects of estrogens on nitric oxide synthase, it is hypothesized that oral contraceptives containing estrogen may augment skeletal muscle blood flow during exercise. Fourteen women (18-40 yrs old; non-smokers) were divided into two groups: Control (CON; sedentary, normal menstrual-cycling women who have not used oral contraceptives for the past 12 mons; n=7), and oral contraceptive users (OC; sedentary women who have been using low-dose estrogen oral contraceptives for ≥12 mons; n=7). In order to examine the chronic effects of OC use on peripheral blood flow, experiments were timed to correspond with the point in the menstrual cycle (or pill cycle) where circulating estradiol levels were low (CON=58.5 and OC=95.7 pg/ml; P>0.05). Measurements of forearm blood flow were obtained from each group, using strain gauge plethysmography, at rest and during an exercise protocol in which intermittent handgrip exercise was performed at 15%, 30%, and 45% of maximum voluntary contraction (MVC). Each contraction lasted 5 sec followed by 15 sec of rest and continued for 5 minutes at each stage. Blood flow measurements were taken during the rest periods and an average value obtained for each workload. Results indicate no difference in forearm blood flow (ml/100cc tissue) at rest (CON=2.7; OC=2.8); however, the hyperemic response to handgrip exercise was significantly (P<0.05) lower in the OC group at 30% (9.0 vs. CON=14.2) and 45% (12.0 vs. CON=17.0) of MVC. Contrary to our hypothesis, these data indicate a compromised hyperemic response in the forearm of OC users. This may be due to the effect of OCs on cutaneous blood flow. Supported by TWU Research Enhancement Program.