MECHANISMS OF SPONTANEOUS BAROREFLEX IMPAIRMENT IN LYON HYPERTENSIVE RATS

This experiment aimed at 1) comparing the spontaneous baroreflex sensi tivity (SBRS) in Lyon genetically hypertensive (LH), normotensive (LN) , and low blood pressure (LL) rats and 2) assessing some aspects of th e mechanisms of its impairment in LH rats. Baroreflex was studied in c ontrol animals after an early chronic converting enzyme inhibition wit h perindopril and after a 4-wk infusion of ANG II in perindopril-treat ed rats. The SBRS was determined with a previously validated method, u sing statistical dependence between blood pressure (BP) and heart rate values recorded in freely moving animals. LH rats exhibited high BP, cardiac hypertrophy, and decreased SBRS (LH, 1.3 +/- 0.2; LN, 2.5 +/- 0.4; LL, 2.2 +/- 0.4 beats .min(-1).mm.Hg-1). Perindopril prevented th e development of hypertension and cardiac hypertrophy and normalized S BRS. BP rose in LH and LL rats after ANG II infusion, but only LH rats , which developed a cardiac hypertrophy, had an impaired SBRS (LH, 1.1 +/- 0.2; LN, 2.5 +/- 0.2; LL, 2.8 +/- 0.3 beats.min(-1).mm.Hg-1). Thi s impairment was partially reversed by an acute ANG II blockade with l osartan. These results demonstrate that high BP does not account for t he decreased SBRS in LH rats. SBRS impairment could result either from cardiac hypertrophy or from the direct effect of ANG II on the barore flex loop.