Growth hormone increases regional coronary blood flow and capillary density in aged rats

In this study, we examined the effects of acre and Growth hormone replaceme nt on both coronary blood flow and capillary density. Blood flow was measur ed by using [C-14]-iodoantipyrine in three groups of anesthetized Brown Nor way X Fischer 344 rats: young vehicle-treated animals (6 months, n = 13), o ld vehicle treated animals (30 months; n = 9), and old animals treated with bovine growth hormone (200 mug/kg) twice a day for 30 days (30 months; n = 7). Capillary density was measured by color segmentation analysis of secti ons stained for platelet endothelial cell adhesion molecule-1. In all regio ns examined, coronary blood flow decreased with age, and growth hormone adm inistration resulted in an increase in flow compared to vehicle-treated ani mals. Capillary density decreased with age in the apex and the left ventric ular middle segment. In response to growth hormone administration, capillar y density increased significantly in the apex but not in other regions of t he heart. Our results demonstrate that Growth hormone enhances regional myo cardial blood flow in the aged heart and suggest that part of this effect c ould be due to an increase in capillary density.