Myocardial capillary diffusion capacity in rat hearts with cardiac hypertrophy due to pressure and volume overload.

The functional adaptation of the myocardial capillary bed in response to cardiac hypertrophy was studied in one volume overload (aortocaval fistula, ACF) and in one pressure overload model [left renal arterial stenosis, two-kidney, one-clip (2K,1C)]. Furthermore, a group where renal hypertension was reversed 1 wk before experimentation (UC-2K,1C) and a sham-operated (Sham) group were studied. Functional estimations of myocardial capillary diffusion capacity in terms of permeability surface area products (PS) per 100 g of myocardium were obtained by the single-injection indicator dilution technique in a Langendorff preparation. After 4 wk, ACF hearts, with 72% hypertrophy and normal minimal coronary vascular resistance (CVR), displayed an unchanged diffusion capacity, i.e., PS for Cr-EDTA and vitamin B12. This indicates a structural out-growth of the coronary vascular bed to match the increased demand of the tissue. 2K,1C hearts with marked elevations of minimal coronary vascular resistance and left ventricular hypertrophy (65%) showed higher PS values than Sham, implying that diffusion capacity was enhanced despite structural coronary vascular changes. These changes were completely reversed in UC-2K,1C. Thus the present data imply that myocardial capillary diffusion capacity was well maintained in volume overloaded cardiac hypertrophy and in contrast with earlier morphometric estimations, even enhanced in pressure overload hypertrophy.