Abstract
Oral contraceptive (OC) use is associated with increased intrarenal renin-angiotensin-aldosterone system (RAA System) activity and risk of nephropathy, though the contribution of progestins contained in the OC in the regulation of angiotensin-dependent control of the renal circulation has not been elucidated. A total of 18 OC users (8 non-diabetic, 10 Type 1 diabetic) were studied in high salt balance, a state of maximal RAA System suppression. Progestational and androgenic activity of the progestin in each OC was standardized to that of the reference progestin norethindrone. Renal plasma flow (RPF) was measured by para-aminohippurate clearance at baseline and in response to angiotensin-converting enzyme (ACE) inhibition. There was a positive correlation between OC progestational activity and the RPF response to ACE inhibition (r=0.52, P=0.03). Similar results were noted with OC androgenic activity (r=0.54, P=0.02). On subgroup analysis, only non-diabetic subjects showed an association between progestational activity and angiotensin-dependent control of the renal circulation (r=0.71, P=0.05 non-diabetic; r=0.14, P=0.7 diabetic; P=0.07 between groups). Similar results were noted with respect to androgenic activity (r=0.88, P=0.005 non-diabetic; r=-0.33, P=0.3 diabetic; P=0.002 between groups). Our results suggest that the OC progestin component is a significant influence on the degree of angiotensin-dependent control of the renal circulation, though these findings may not apply to women with diabetes.