WEYRICH, A. S., W. J. REJESKI, P. H. BRUBAKER, and J. S. PARKS. The effects of testosterone on lipids and eicosanoids in cynomolgus monkeys.Med. Sci. Sports Exerc., Vol. 24, No. 3, pp. 333–338, 1992. The effect of testosterone administration on plasma lipoproteins and eicosanoids was studied in 24 male cynomolgus monkeys. We hypothesized that elevated plasma testosterone would unfavorably alter plasma lipids as well as thromboxane A2(TxA2) and prostacyclin (PGI2), two eicosanoids that have been linked to the increased incidence of atherosclerosis, myocardial ischemia, and thrombosis. To test our hypothesis, half of the monkeys (N =12) were subjected to 10 wk of testosterone treatment, whereas the remaining monkeys (N= 12) received a sesame oil vehicle. The plasma concentrations of thromboxane B2(TxB2) and 6-keto-PGFIalpha, the stable metabolites of TxA2and PGI2, respectively, were determined. Additionally, assays were conducted on total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), and triglycerides (TG). Distribution of the HDL subfraction protein was measured by gradient gel electrophoresis. All monkeys exhibited significant increases in TC (P< 0.001) and low density lipoprotein cholesterol (LDL-C) (P< 0.001); however, monkeys who received testosterone also displayed significant increases in TxB2(P< 0.03) and decreases in HDL-C (P< 0.03) compared with control monkeys. There was a trend in the HDL-C subfraction data, indicating that testosterone treatment may be associated with a decrease in the larger HDL2bsubfraction and a corresponding increase in HDL3c. These results demonstrate that exogenous testosterone adversely alters cardiovascular risk profiles by increasing TXB2production and decreasing HDL-C. Athletes who use testosterone as an anabolic androgenic steroid may have an increased risk for coronary heart disease.