Estradiol is a potent inhibitor of the hypotriglyceridemic effect of levonorgestrel in female rats.

The progestin, levonorgestrel, when administered to rats intramuscularly, significantly lowered both total and very low density lipoprotein triglyceride concentrations in the blood plasma by 35-40%. This effect was readily abolished by the simultaneous intramuscular administration of estradiol benzoate. Similarly, estradiol-17 beta overcame the inhibitory effects of levonorgestrel on the incorporation of [9,10-3H]palmitate into triglycerides of freshly isolated rat hepatocytes studied in vitro. However, estradiol alone significantly raised plasma triglycerides by two-fold in vivo. Estradiol also significantly enhanced (by 9%) the incorporation of [9,10-3H]palmitate into hepatocyte triglycerides. These results suggest that the effects of estradiol on triglyceride synthesis and concentration dominate over those of levonorgestrel in the rat.