Chronic rejection in rat aortic allografts. IV. Effect of hypercholesterolemia in allograft arteriosclerosis.

Rat aortic allografts transplanted across histoincompatible strains develop arteriosclerotic alterations in the vascular wall that are virtually indistinguishable from those observed in human heart allografts during chronic rejection. In this study we have investigated whether hypercholesterolemia in the recipient rat accelerates allograft arteriosclerosis. Hypercholesterolemia was induced by a 4% cholesterol and 0.5% cholic acid diet, added to the normal rat diet. The cholesterol and cholic acid diet increased the level of serum total cholesterol from 1.3 +/- 0.0 to 4.8 +/- 0.9 (+/- SD) mmol/L and the level of low-density lipoprotein cholesterol from 0.3 +/- 0.0 to 2.6 +/- 1.0 mmol/L (p < 0.05) but caused no change in the level of high-density lipoprotein cholesterol, 1.0 +/- 0.1 versus 0.7 +/- 0.3 mmol/L. The level of plasma triglycerides remained also unchanged. Quantitation of two major chronic rejection-associated eicosanoids from the allograft vascular wall showed a significant increase in the synthesis of thromboxane B2 in the hyperlipidemic animals from 6.0 +/- 5.0 to 8.0 +/- 5.0 ng/mg dry weight and a slight reduction in the synthesis of 6-keto-prostaglandins F1 alpha. In vivo labeling of the recipient rat with tritiated thymidine and autoradiography showed that hypercholesterolemia did not affect the proliferation of inflammatory cells in the allograft adventitia, slightly increased the proliferation of smooth muscle cells in the media from 23 +/- 14 cells to 34 +/- 13 cells (+/- SEM) per cross section (p = ns), but slightly reduced the proliferation of smooth muscle cells in the intima from 13 +/- 6 to 6.2 +/- 1.5 (p = ns). Hypercholesterolemic recipients did not show any significant enhancement but, in fact, showed a delay in the generation of arteriosclerotic changes in the allograft intima. We conclude that although hypercholesterolemia, in the absence of hypertriglyceridemia, induces significant alterations in the eicosanoid metabolism and minor alterations in smooth muscle cell proliferation in the transplant vascular wall, it does not enhance arteriosclerotic alterations in chronically rejecting rat aortic allografts.