RAT OVARIAN ANGIOTENSIN-II RECEPTORS, RENIN, AND ANGIOTENSIN I-CONVERTING ENZYME DURING PREGNANCY AND THE POSTPARTUM PERIOD

The ovarian renin-angiotensin system (RAS) has been studied extensively in the virgin cycling rat, but little information is available about this system in pregnant and postpartum rats. We show that renin and angiotensin I-converting enzyme (ACE)- the key enzymes involved in angiotensin II (Ang II) formation-and Ang II receptors, are present in pregnant and postpartum rat ovaries. From gestation Days 2-4 to 10-12, active ovarian renin ranged from 1.12 +/- 0.13 to 1.27 +/- 0.19 ng Ang I/h/mg and comprised between 68 and 86% of total (active + inactive) ovarian renin activity. Between Days 10-12 and Days 14-16 of pregnancy, ovarian active renin activity increased slightly, but inactive renin disappeared, suggesting its activation; the remaining active renin then decreased 62% by Days 18-20 (p < 0.05). On postpartum Day 2, both active and total ovarian renin activity exceeded that of Days 2-20 of pregnancy (p < 0.05); levels of both then declined sharply by postpartum Day 3 (p < 0.05). In pregnant rats, levels of ovarian Ang II receptors, identified by the specific binding of [I-125]-[Sar1,Ile8]Ang II to ovarian membranes, were high between Days 2-4 and 10-12 of pregnancy, ranging from 12.8 +/- 1.7 to 15.7 +/- 3.4 fmol/mg, but steadily declined by 82% between gestation Days 10-12 and 18-20 (p < 0.05). Postpartum Ang II receptor levels on Days 2, 3, and 4 showed a gradual increase from low levels comparable to Days 18-20 of pregnancy. Ovarian ACE activity did not change throughout pregnancy or during the postpartum period. Plasma active and total renin activity tended to be higher during pregnancy than during postpartum Days 3 and 4. The presence in pregnant and postpartum rat ovaries of active renin, ACE, and Ang II receptors, as well as changes in active renin and Ang II receptors, suggest that Ang II may regulate ovarian function in pregnant and postpartum rats.