IMPORTANCE OF CARDIAC, BUT NOT VASCULAR, HYPERTROPHY IN THE CARDIAC BAROREFLEX DEFICIT IN SPONTANEOUSLY HYPERTENSIVE AND STROKE-PRONE RATS

In the present study, we examined whether antihypertensive treatment of young and adult hypertensive rats with the angiotensin-converting enzyme (ACE) inhibitor perindopril could restore the baroreflex vagal deficit and whether this was related to prevention of cardiac or vascular hypertrophy. Spontaneously hypertensive (SHR), stroke-prone spontaneously hypertensive (SHR-SP), and Wistar-Kyoto (WKY) rats were untreated or treated with perindopril (3 mg/kg/day) in the drinking water from 4-9 and from 14-20 weeks of age. Steady-state sigmoidal mean arterial pressure (MAP)-heart rate (HR) reflex curves were obtained in the conscious rats by the injection of pressor and depressor agents before and after atenolol (vagal component). Increased left ventricle to bodyweight ratio (LV/BW) indicated cardiac hypertrophy. After ganglion blockade, the minimum MAP produced by nitroprusside and the maximum produced by methoxamine were used as indications of vascular hypertrophy. Perindopril treatment reduced cardiac and vascular hypertrophy to different extents in SHR and SHR-SP. The 4-9 and 14-20 week treatments reduced MAP and both minimum and maximum blood pressure of the SHR to the levels of the untreated WKY. However, only in the older animals was LV/BW restored. In the SHR-SP, early treatment had a much greater effect on vascular hypertrophy than on LV/BW. The reverse occurred for the 14-20 week animals. In untreated hypertensive animals the baroreflex curves were shifted to the right with reduced vagal HR range. Perindopril treatment shifted the baroreflex curves back towards the WKY curves. Vagal HR range was strongly correlated with the LV/BW, whereas vagal HR range was less well related to the level of vascular hypertrophy or blood pressure. These results suggest that antihypertensive treatment can restore cardiac baroreflex function and that it is related to the reduction in cardiac hypertrophy. Although the mechanism of this relationship remains to be elucidated, these findings suggest that cardiac vagal afferents may be important.