Purpose: A local renin angiotensin (ANG) system has been identified in the bladder. To our knowledge little is known about this system. To define further the physiology of this system we performed this study.
Materials and methods: The circulating and bladder tissue concentrations of ANG I and ANG II were examined in anesthetized Sprague-Dawley female rats in estrus, diestrus or pregnancy. Each was given an intravenous bolus infusion of ANG I, the ANG converting enzyme inhibitor enalaprilat or saline.
Results: The mean concentrations of ANG I and ANG II were markedly higher in bladder tissue than in whole blood at the highest levels in pregnancy. The concentration of ANG I and ANG II increased significantly in the bladder tissue and circulation after the ANG I infusion in estrus and diestrus. In pregnancy only circulatory ANG I increased, while circulatory ANG II, tissue ANG I and ANG II remained unchanged. Enalaprilat infusion was associated with an increased concentration of whole blood ANG I in all groups and decreased plasma ANG II in estrus and diestrus but not in pregnancy. The bladder tissue ANG I response was unchanged in all groups. Bladder tissue ANG II was decreased in estrus and diestrus but unchanged in pregnancy.
Conclusions: These data support the hypothesis that ANG converting enzyme is deactivated and an alternate pathway is activated in pregnancy. The data also demonstrate that tissue absorption of ANG peptide is diminished in pregnancy. Compared with responses in similarly studied male rats the circulating conversion of ANG I to ANG II is delayed in female rats and responses to ANG converting enzyme inhibition are enhanced, thus, suggesting subtle differences in the sexes in the renin ANG system. Enalapril appears to have more effect at the tissue level in nonpregnant females than in pregnant females and male rats.