EFFECT OF CONTRACEPTIVE STEROID AND ENALAPRIL TREATMENT ON SYSTOLIC BLOOD-PRESSURE AND PLASMA RENIN-ANGIOTENSIN IN THE RAT

Previous work has demonstrated contraceptive steroid-induced hypertens ion in rats. Here, we examined the relationship between steroid-induce d hypertension and components of the renin-angiotensin system. Female Sprague-Dawley rats were injected s.c. with 0.2 mu g ethynyloestradiol , 2.0 mu g levonorgestrel, a combination of both or vehicle, six days per week. A second group of rats received 2.0 mu g enalapril maleate, enalapril plus ethynyloestradiol or levonorgestrel, or vehicle. Systol ic blood pressure increased with both ethynyloestradiol (6 weeks, +17 mmHg; 12 weeks, +32 mmHg) and levonorgestrel (6 weeks, +24 mmHg) treat ment. This effect of levonorgestrel was attenuated by co-administratio n of enalapril, which also reversed the hypertension seen with ethynyl oestadiol. Ethynyloestradiol, but not levonorgestrel treatment caused a significant increase in plasma renin concentration, plasma renin act ivity, and plasma angiotensin II at both 6 and 12 weeks. Plasma renin substrate was increased by ethynyloestradiol at 3, 6 and 12 weeks, pri or to the observed increase in systolic blood pressure. Combined stero id treatment had less pronounced effects. Enalapril alone or in combin ation with ethynyloestradiol decreased plasma renin concentration, act ivity and angiotensin II, and in combination with levonorgestrel decre ased plasma renin concentration, substrate and activity (6 weeks only) but not angiotensin II. The data indicate a positive relationship bet ween hypertension and the renin-angiotensin system with ethynyloestrad iol, but not levonorgestrel treatment in rats.