Steroidogenic activity, insulin-like growth factor-I production, and proliferation of granulosa and theca cells obtained from dominant preovulatory and nonovulatory follicles during the bovine estrous cycle: effects of low-density and high-density lipoproteins.

The role of high- and low-density lipoproteins (HDL and LDL) in regulating steroidogenic activity, cellular viability and proliferation, and insulin-like growth factor-I (IGF-I) production was examined in granulosa and theca cells from dominant preovulatory (DO) and nonovulatory (DNO) bovine follicles. Follicles were obtained from pluriparous nonlactating beef cows at ovariectomy 24 h after administration of a luteolytic dose of prostaglandin F2 alpha (DO) or during the first follicular wave on Days 5-8 of the estrous cycle (DNO). Lipoprotein effects on hormone production (ng/1.5 x 10(5) viable cells) and cell viability were studied in serum-free, defined medium containing LH and FSH (granulosa) or LH only (theca). During late stages (96-144 h) of culture, HDL in the presence of gonadotropins increased (p < 0.001) the production of progesterone by granulosa and theca cells and the production of IGF-I by granulosa cells. LDL did not stimulate granulosa or thecal progesterone synthesis and attenuated HDL-stimulated progesterone production by both cell types. Gonadotropin stimulation of terminal synthetic pathways was either attenuated (granulosa estradiol production) by addition of lipoproteins or maximally stimulated (theca cell androstenedione production) by a combination of LDL and HDL. Both lipoproteins increased (p < 0.05) granulosa cell viability in both follicle types, and a marked proliferation (p < 0.001) of steroidogenically inactive theca cells was observed from DO but not DNO follicles. Proliferation potential appeared to be switched off during the late stages of maturation of DNO follicles and switched on after induced luteal regression and rescue of DO follicles.