Myocardial capillary density in hypertensive rats

The density of myocardial capillaries was determined in spontaneous hypertensive (SHR) and age-matched normotensive Wistar-Kyoto (WKY) rats. Standard procedures were used to determine the systolic blood pressure of the animals. Specimens for light microscopic studies were sampled from the middle portion of the left ventricular free wall of in situ K+-arrested, glutaraldehyde-fixed hearts. The heart weight of SHR rats did not reveal significant hypertrophy as compared to WKY rats, despite the high systolic blood pressure recorded in the SHR. The mean capillary density was found to be 18,514 +/- 341 in SHR and 18,128 +/- 362 in WKY. Transmural gradient was apparent in the left ventricular free wall of both animal groups. The capillary density declined with age in both SHR and WKY. The data indicate that the myocardium of both normotensive and hypertensive rats contain a high capillary density per sq. millimeter. In addition, the data suggest that: (1) the number of capillaries per unit area is unchanged in spontaneous hypertension, and (2) pressure overload of modest magnitude does not induce detectable myocardial hypertrophy.