Endothelial morphology and plasma total and high density lipoprotein cholesterol changes in hypothalamically stimulated squirrel monkeys fed a modified atherogenic diet.

Experimental animals fed atherogenic diets show endothelial damage, impairment of endothelial regeneration and plasma lipid changes characterized by elevation of LDL and decrease of HDL cholesterol concentrations. Previous studies in this laboratory disclosed that chronic electrical stimulation of the lateral hypothalamus was associated with electron-microscopic evidence of endothelial injury in rats and squirrel monkeys maintained on basal (low fat/cholesterol-free) diets. In the present investigation squirrel monkeys fed similar diets supplemented with "modest" amounts of caloric fat and cholesterol were subjected to chronic lateral hypothalamic stimulation for periods as long as 20 months with the expectation that endothelial injury would be greater than in the absence of the supplements. The expectations were not substantiated. Endothelium was found to be surprisingly intact by electron microscopy and similar to that of implanted nonstimulated controls. A further observation of interest was the cholesterolemic response, notably in the HDL fraction, observed in both groups, but more striking in experimental animals. The data suggest that an interaction between a modified lipid/cholesterol diet and hypothalamic stimulation may lead to elevation of plasma HDL cholesterol concentration and preservation of endothelial integrity. Further investigation is required to determine whether these two events are causally related.