Reversal of the suppressed kidney renin level in the hypertensive transgenic rat tgr(mRen-2)27 by angiotensin converting enzyme inhibition

Abstract

The transgenic rat TGR(mRen-2)27 develops severe hypertension with high adrenal renin and low kidney renin. The mechanism of suppressed kidney renin in these animals is still unclear. We investigated the effect of the angiotensin converting enzyme (ACE) inhibitor, perindopril on the renin-angiotensin system in plasma and tissues (adrenal gland and kidney), and the effect of mouse renin antibody on plasma and tissue renin activity before and after perindopril administration. Perindopril lowered blood pressure in the TGR(mRen-2)27 rats from 254.5 +/- 7.4 mm Hg to 154 +/- 7.8 mm hg (n = 8, P < .0001), while blood pressure in the untreated TGR (mRen-2)27 rats increased from 253.7 +/- 8.1 to 276.1 +/- 14.3 mm Hg during the study period. Perindopril significantly suppressed plasma angiotensin II (Ang II) from 19.4 +/- 2.5 pg/mL to 2.6 +/- 0.4 pg/mL, P < .0001, while markedly increasing plasma renin concentration (PRC) from 15.5 +/- 1.8 ng AngI/mL/h to 148.2 +/- 35.5 ng AngI/mL/h, P < .005 and kidney renin from 56.7 +/- 18.1 micrograms AngI/g/h to 827.4 +/- 79.1 micrograms AngI/g/h, P < .0001. However, adrenal renin was not increased. A mouse Ren-2 renin antibody at a 1:1000 dilution that suppresses purified mouse Ren-2 renin activity by 62.6 +/- 3.6% (n = 3, P < .0001) and does not suppress renin activity in plasma and kidney of the Sprague-Dawley rats, suppressed PRC in the untreated TGR(mRen-2)27 rats by 52.3 +/- 3.5% (n = 6, P < .0001). However, it only suppressed PRC in the perindopril treated TGR(mRen-2)27 rats by 7.0 +/- 2.4% (n = 6, P < .05). The antibody suppressed adrenal renin in both untreated and perindopril treated TGR(mREN-2)27 rats by 57.3 +/- 5.4% (n = 5, P < .0001) and 49.7 +/- 2.2% (n = 6, P < .0001), respectively. On the other hand, the mouse antibody suppressed kidney renin in the untreated TGR(mRen-2)27 rats by only 11.0 +/- 3.3% (n = 6, P < .05), and did not suppress kidney renin in the perindopril treated TGR(mRen-2)27 rats (n = 6, P < .0001), respectively. On the other hand, the mouse antibody suppressed kidney renin in the untreated TGR(mRen-2)27 rats by only 11.0 +/- 3.3% (n = 6, P < .05), and did not suppress kidney renin in the perindopril treated TGR(mRen-2)27 rats (n = 6, P < NS). The pH profile of renin activity in plasma confirmed the results of the antibody study. We conclude that in the TGR(mRen-2)27 rats adrenal renin is mainly mouse renin and kidney renin is mainly rat renin. The main sources of circulating renin in the TGR(mRen-2)27 rats are extra-renal tissues, including the adrenal glands, where mouse Ren-2 renin transcripts are highly expressed. The increased circulating renin in perindopril treated TGR(mRen-2)27 rats is rat renin derived from the kidney. The failure of adrenal renin to increase with perindopril suggests that at least in the basal state there is no feedback inhibition as there is in the kidney. The low kidney renin appears to be due to physiological rather than genetic factors.