Susceptibility to apoptosis measured by MYC, BCL-2, and BAX expression in arterioles and capillaries of adult spontaneously hypertensive rats.

Hypertension results in microvascular rarefaction or disappearance of microvessels. In the present study, we investigated the pathogenic role of apoptosis in hypertension-induced rarefaction of heart arterioles and capillaries of spontaneously hypertensive rats (SHR). Experiments were performed on hearts from 6-week-old, 16-week-old, and 30-week-old SHR (n = 30 rats) (SHR6, SHR16, SHR30). We used as controls 6-week-old, 16-week-old, and 30-week-old normotensive rats (WKY) (n = 30 rats) (WKY6, WKY16, WKY30). We analyzed the expression of c-myc, bcl-2, and bax and in situ end-labeling DNA fragmentation in vascular smooth muscle cells of arterioles and endothelial cells of arterioles and capillaries. Endothelial cells of capillaries and endothelial and smooth muscle cells of arterioles of hypertensive animals (SHR) express more Bax protein and Myc protein than their respective normotensive controls by margins that were statistically significant. The SHR30 group expressed the lowest levels of Bcl-2 protein by a margin that was statistically significantly different from WKY30. We did not find evidence of apoptosis in arterioles or capillaries on the basis of in situ end-labeling. However, our results indicated that alterations in the expression of members of the Bcl-2 family of proteins and Myc protein occurred in smooth muscle cells and endothelial cells of arterioles and capillaries of SHR. In conclusion, although evidence of apoptosis in arterioles and capillaries was not found by in situ end-labeling, our findings suggest that in hypertension they may have a higher susceptibility to apoptosis, and therefore rarefaction may be a consequence of apoptosis.