High blood pressure maintenance in transgenic mRen-2 vs. Lyon genetically hypertensive rats

The present work was aimed to assess the factors involved in the maintenance of hypertension in adult transgenic mRen-2 (TG) rats. Special attention was paid to the renal handling of sodium, the sympathetic, and the renin-angiotensin system (RAS) activity. TG rats were compared with age-matched Lyon genetically hypertensive rats (LH), as both are of Sprague-Dawley origin. Blood pressure (BP), heart rate, and renal sympathetic nerve activity (RSNA) were recorded in conscious freely moving animals. Kidneys were isolated and single-pass perfused at different pressure levels. It was observed that the peripheral sympathetic drive was identical in TG and LH rats as indicated by their similar 24-h urinary excretion of catecholamines and methoxylated metabolites, baseline RSNA and its control by the baroreflex, and hypotensive response to ganglion-blockade. On the contrary, TG rats differed from LH rats by a more rapid excretion of an oral isotonic sodium load, a greater hypotensive and natriuretic response to furosemide, and a more marked BP response to acute RAS blockade. The TG kidney responses to stepwise changes in renal perfusion pressure (RPP) differed from those of LH rats by significantly higher perfusate flow and glomerular filtration rate. However, the pressure natriuresis curve of TG kidneys did not differ from that of LH rats because of an elevated tubular sodium reabsorption rate. These results suggest that adult TG rats, compared with LH rats, exhibit a tendency toward sodium and water retention, which may explain that despite low renal and circulating renin levels, the RAS remains involved in the maintenance of high BP in that model.