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 regula ting steroidogenic activity, cellular viability and proliferation, and insulin-like growth factor-I (IGF-I) production was examined in granu losa and theca cells from dominant preovulatory (DO) and nonovulatory (DNO) bovine follicles. Follicles were obtained from pluriparous nonla ctating beef cows at ovariectomy 24 h after administration of a luteol ytic dose of prostaglandin F-2 alpha (DO) or during the first follicul ar 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 w ere studied in serum-free, defined medium containing LH and FSH (granu losa) or LH only (theca). During late stages (96-144 h) of culture, HD L in the presence of gonadotropins increased (p < 0.001) the productio n of progesterone by granulosa and theca cells and the production of I GF-I by granulosa cells. LDL did not stimulate granulosa or thecal pro gesterone synthesis and attenuated HDL-stimulated progesterone product ion by both cell types. Gonadotropin stimulation of terminal synthetic pathways was either attenuated (granulosa estradiol production) by ad dition of lipoproteins or maximally stimulated (theca cell androstened ione production) by a combination of LDL and HDL, Both lipoproteins in creased (p < 0.05) granulosa cell viability in both follicle types, an d a marked proliferation (p < 0.001) of steroidogenically inactive the ca cells was observed from DO but not DNO follicles. Proliferation pot ential appeared to be switched off during the late stages of maturatio n of DNO follicles and switched on after induced luteal regression and rescue of DO follicles.