The urinary bladder angiotensin system: Response to infusions of angiotensin I and angiotensin-converting enzyme inhibitors

The circulating and urinary bladder tissue concentrations of angiotensin I (ANG I) and angiotensin II (ANG-(1–8)] were examined in anesthetized Sprague-Dawley male rats given an intravenous bolus infusion of either ANG I, the angiotensin-converting enzyme (ACE) inhibitors enalaprilat or ramiprilat, or saline. The mean concentrations of ANG I and ANG-(1–8) were markedly higher in the urinary bladder tissue than in whole blood. There was a significant increase in the concentration of ANG I and ANG-(1–8), both in the urinary bladder tissue and the circulation, after the ANG I infusion. Both ACE inhibitors were associated with an increase in the concentration of whole blood ANG I; however, tissue ANG I levels were significantly increased only following ACE inhibition with ramiprilat but not with enalaprilat. Both plasma and urinary bladder tissue ANG-(1–8) levels decreased significantly following ACE inhibition, but only with ramiprilat. The elevated urinary bladder tissue levels of ANG I and ANG(1–8) at baseline, compared with circulating levels, and the maintenance of ANG-(1–8) in bladder tissue in the face of inhibition of the circulatory renin-angiotensin system with enalaprilat support the presence of an autocrine/ paracrine renin-angiotensin system in the urinary bladder. Under the current experimental conditions, ramiprilat appears to have enhance bladder activity compared with enalaprilat.