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In an attempt to establish a defined model system for studies aimed at elucidating the mechanism of PGF2 alpha action, we examined the effects of medium supplementation with soluble hydroxycholesterol analogues, alone and in combination with ovine luteinizing hormone (oLH) in the presence and absence of PGF2 alpha, on progesterone secretion by mixed ovine luteal cells in vitro. In short-term cultures (2-6 h), supplementary 22R-hydroxycholesterol (22R-OHC; 0.16-20 micrograms ml-1) increased (P &lt; 0.05) progesterone production in a dose-dependent manner, whereas similar concentrations of 22S-hydroxycholesterol (22S-OHC) and 25-hydroxycholesterol (25-OHC) had little effect. In incubations of &lt; or = 24 h duration, 22R-OHC (1 micrograms ml-1) dramatically increased progesterone secretion, whereas oLH (100 ng ml-1) in the presence or absence of PGF2 alpha (250 ng ml-1) had no consistent effects, alone or in combination with 22R-OHC. In contrast, 22R-OHC (1 micrograms ml-1) alone had no effect in long-term incubations (72-192 h), nor did treatment with oLH (100 ng ml-1) in the presence or absence of PGF2 alpha (250 ng ml-1) in the absence of 22R-OHC. Together, however, 22R-OHC and oLH stimulated (P &lt; 0.05) progesterone secretion, a synergistic effect consistently inhibited (P &lt; 0.05) by PGF2 alpha. Equimolar (2.5 mumol l-1) concentrations of 22R-OHC and homologous serum low- or high-density lipoprotein cholesterol exhibited comparable capacities to maintain progesterone secretion in long-term cultures (24-168 h), with and without gonadotrophin (oLH or human chorionic gonadotrophin, 100 ng ml-1) stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

reproduction

Effects of substrate supplementation with hydroxycholesterol analogues and serum lipoproteins on ovine luteal cell progesterone secretion in vitro: demonstration of prostaglandin F2 luteolytic actions in a defined model system