Sympathectomy stimulates capillary but not precapillary growth in hypertrophic hearts

Abstract

Sympathetic nerves are known to influence vascular growth, but their role in coronary vascular adaptations to pressure-overload left ventricular (LV) hypertrophy is unknown. Accordingly, regional sympathectomy (SYMX) was produced by painting a ring of phenol on the posterior third of the LV in seven renal hypertensive (Page: 1 kidney, 1 wrap) and seven normotensive (sham: 1 kidney, no wrap) rabbits. Two months later, maximal myocardial blood flow (MBF) following dipyridamole-induced coronary vasodilation was determined with microspheres in the intact anterior and the sympathectomized posterior regions of conscious rabbits. Histomorphometric methods were then utilized to evaluate capillary density (CD), intercapillary distance (ICD), and volume density (VD) of subepicardial and endocardial samples of each region of perfused-fixed hearts. The Page procedure significantly increased systolic blood pressure (+29%) and LV wt/body wt (+20%) above sham rabbits. In both sham and Page groups, MBF was not significantly different between intact and sympathectomized regions within either group. SYMX did not significantly alter CD, ICD, or VD between regions in the sham animals. In contrast, SYMX significantly increased CD (+30%) and VD (+26%) and decreased ICD (-21%) in the subendocardial region of Page animals. Regional SYMX did not alter myocyte cross-sectional area in Page animals. We conclude that SYMX neither 1) significantly increases resistance vessel cross-sectional lumen area in either normal or hypertrophic hearts, nor 2) significantly influences capillary growth in normal hearts, but SYMX does 3) promote capillary growth in hearts undergoing hypertrophy in response to hypertension.