Long-term pressure-induced cardiac hypertrophy: capillary and mast cell proliferation.

To determine whether a prolonged duration of mechanical load on the ventricular myocardium leads to capillary proliferation, constriction of the pulmonary artery was produced in rats at 3 mo of age, and the hearts were examined 200 days later. Functionally, elevations of right ventricular systolic pressure, from 30 +/- 12 to 67 +/- 11 mmHg, and right ventricular end-diastolic pressure, from 2.4 +/- 1.4 to 8.6 +/- 2.4 mmHg, were found. Anatomically, a 69% enlargement in right ventricular mass was observed, and this hypertrophic growth was characterized by a 78% thickening of the wall with no change in ventricular wall area, the latter calculated from the quotient of ventricular volume and wall thickness. Morphometric data showed a 44% increase in the capillary-to-myocyte ratio, a 66% augmentation of the total length of capillaries in the whole ventricle, and a 77% greater number of capillaries across the ventricular wall. Furthermore, these indexes of neogenesis of capillary units were associated with a more than three fold increase in the numerical density of mast cell profiles in the myocardium. In conclusion, capillary proliferation occurs in the adult rat heart, and this process appears to be coupled with mast cell hyperplasia.