Testosterone regulates metabolism of plasma chylomicrons in rats

Previously we demonstrated a marked sex difference in the metabolism of chylomicrons in adult rats. In males, radiolabeled chylomicrons displayed a longer dwell time on endothelial surfaces, which resulted in a decreased chylomicron uptake by the liver. The increased rate of chylomicron metabolism in females was associated with increased postheparin lipoprotein lipase activity. In the present study, we have investigated the effects of physiological doses of sex steroid hormones on the metabolism of chylomicrons and postheparin lipoprotein lipase activity. No sex differences were found in prepubertal animals. We also found no difference in chylomicron metabolism in control female, castrated female, estrogen-treated female, castrated male, and estrogen-treated male rats. However, control male, testosterone-treated male, and testosterone-treated female rats showed increased endothelial binding of chylomicrons and decreased chylomicron uptake by the liver. Postheparin lipoprotein lipase activity also was decreased by testosterone administration. In parallel with the alterations in chylomicron metabolism, serum high density lipoprotein levels in male rats decreased with testosterone administration. These results indicate that the differences in chylomicron metabolism, postheparin lipoprotein lipase activities, and serum high density lipoprotein levels observed between male and female rats are due to testosterone.