Dipyridamole-induced capillary growth in normal and hypertrophic hearts.

Chronic increases in myocardial blood flow have been shown to stimulate capillary proliferation in normal growing hearts. It is unknown, however, if elevated myocardial blood flow stimulates precapillary and/or capillary growth in hearts undergoing hypertrophy. Accordingly, renal hypertension was produced in rabbits (Page, 1-kidney, 1-wrap model) in which one group of Page (n = 9) and one group of normotensive sham (n = 10) rabbits were given dipyridamole (4.0 mg/kg sc) twice daily for 2 mo. Another group of Page (n = 7) and sham (n = 12) rabbits received vehicle injections. In separate acute studies performed on conscious rabbits, this does of dipyridamole increased myocardial blood flow 35-60% over time without altering transmural distribution of flow or systemic blood pressure. Two months later, minimal coronary vascular resistance (MCVR/100 g) was calculated from perfusion during maximal coronary vasodilation in conscious animals. Histomorphometric methods were then utilized to evaluate various indexes of capillarity in perfuse-fixed hearts. Systolic pressure and left ventricle weight-to-body weight ratios were significantly higher in Page vs. sham rabbits; dipyridamole treatment did not alter these parameters within either group. Similarly, dipyridamole treatment did not significantly alter MCVR/100 g values in either normotensive or hypertensive rabbits. In contrast, dipyridamole treatment increased endomyocardial capillary length density by 33% in the hypertensive group (P less than 0.05) and 11% in the sham group (P not significant) compared with the respective vehicle-treated rabbits. In addition, intercapillary distance was significantly reduced in the endomyocardial region of both groups receiving dipyridamole injections.(ABSTRACT TRUNCATED AT 250 WORDS)