Effect of Lipoproteins, 25-Hydroxycholesterol and Luteinizing Hormone on In Vitro Follicular Steroidogenesis in the Hamster and Rat

In 4-h incubations with the medium changed every hour, proestrous Graafian follicles of the rat secreted greater amounts of progesterone (P4), androstenedione (delta) and estradiol (E2) than the hamster follicle (at H 1: 3.5, 3.6, 2.5 times, respectively). Follicles isolated from both species responded to 10-100 micrograms of human high-density lipoprotein (HDL) by enhanced P4 production, whereas these doses of HDL augmented delta and E2 secretion only in the hamster. One mg of human low-density lipoprotein (LDL) was as potent as 100 micrograms of HDL in stimulating P4 secretion in the hamster, but was unable to increase steroid synthesis in the rat. One to 50 micrograms of 25-hydroxy-cholesterol (25-OH) enhanced P4, delta and E2 secretion in a dose-dependent manner in the hamster follicle, but was without effect in the rat. In the hamster, 10-100 ng of luteinizing hormone (LH) increased steroid secretion in a dose-related fashion, while the rat follicle only responded to 100 ng of LH and the hamster follicle was much more responsive than the rat follicle. The responsiveness of the hamster follicle to 50 micrograms of 25-OH was less than to 100 ng LH (P4 production after LH stimulation was 12-fold greater than that after 25-OH stimulation). There was no additive effect of LH and HDL on follicular steroidogenesis in either species. A pharmacological dose of LDL (1000 micrograms) negated the stimulatory effect of LH on follicular steroidogenesis in both species, especially P4.(ABSTRACT TRUNCATED AT 250 WORDS)