Effects of antihypertensive drugs on heart and resistance vessels

STUDY OBJECTIVE - The aim of the study was to examine the effects of antihypertensive drugs on heart and resistance vessels to see whether regression of peripheral vascular hypertrophy accompanies reduction in cardiac mass. DESIGN - Matched groups of spontaneously hypertensive and control rats were treated for 12 weeks with captopril (average dose 65 mg.kg-1.d-1) or hydrochlorothiazide (73 mg.kg-1.d-1) and compared to untreated groups. Perfusion pressure, which has been validated as an index of hypertrophy of resistance vessels, was determined in hind limbs of pithed rats at constant blood flow and maximum vasodilatation. SUBJECTS - Experimental animals were 14 week old male spontaneously hypertensive (SHR) rats (n = 41) and strictly age matched Wistar Kyoto rats (n = 12). SHR rats were assigned at random to three groups: (a) captopril treated (n = 15), (b) hydrochlorothiazide treated (n = 15), (c) control (n = 11). MEASUREMENTS and RESULTS - Mean perfusion pressure was 29.5(SEM 0.4) mm Hg in untreated Wistar Kyoto rats and 37.4(0.5) mm Hg in untreated SHR rats. In comparison with untreated SHR rats, treatment with captopril lowered blood pressure, perfusion pressure [35.2(0.3) v 37.4(0.5) mm Hg, p less than 0.01)], and left ventricular to body weight ratio [2.28(0.03) v 2.63(0.05) mg.g-1, p less than 0.01)]. Treatment with hydrochlorothiazide also lowered blood pressure but had no significant effect on left ventricular weight to body weight ratio [2.54(0.04)]. However, perfusion pressure was reduced to 35.3(0.5) mm Hg, p less than 0.01. CONCLUSIONS - For equal regression of vascular hypertrophy, captopril and hydrochlorothiazide had different effects on regression of left ventricular hypertrophy. Thus left ventricular and vascular structural changes may respond differently to the same drug in the same animal.