Effects of chronic oral contraceptive treatment on the conversion of angiotensin I to angiotensin II in the rat.

The effects of chronic ingestion of oral contraceptive preparations with "low" and "high" estrogen contents on conversion of angiotensin I (AI) to angiotensin II (AII) have been examined in the rat. The dosage employed was 1.0 mg/kg/day for a period of 3 to 4 weeks. Blood pressure responses in anesthesized animals showed that in vivo conversion of AI was increased by about 40% with either drug treatment. The activity of injected renin was increased to the same extent as that of AI following treatment with the low-estrogen preparation, and to a greater extent following treatment with the high-estrogen preparation. Blood pressure responses to AII were also slightly increased above control values in those animals which received high-estrogen treatment. However, conversion of AI in isolated perfused lungs or in plasma from treated rats was not significantly altered from normal. It is concluded that conversion of AI to AII can constitute the rate-limiting step in AII production under certain circumstances and that increased conversion may play a part in the changes in the renin-angiotensin system associated with high circulating estrogen levels. The increased conversion is unlikely to be due to a change in pulmonary or plasma converting enzyme activity.