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Effect of prostaglandin F-2 on steroidogenesis by porcine corpora lutea

Summary. The relationship between luteal cholesterol bound to cytochrome P450_scc enzyme and progesterone production was studied in the pig. Luteal progesterone peaked on Day 10 of the oestrous cycle, declined slowly until Day 13 and then precipitously between Days 13 and 14. The P450_scc was nearly saturated with cholesterol between Days 4 and 13, but changed abruptly by Day 14 to a partly depleted state which persisted until Day 16. Total P450_scc did not decline significantly until Day 17. There was no change in cholesterol esterase activity in a 105 000 g supernatant or in total mitochondrial cholesterol during this period.

Intravenous administration of PGF-2 to hysterectomized gilts resulted in a rapid depletion of cholesterol from P450_scc with a half-life of about 2 h. The new level of cholesterol-P450_scc interaction (less than 45% of cytochrome) persisted for at least 36 h after treatment. This was paralleled by declines in plasma and luteal progesterone.

These results are compatible with the hypothesis that PGF-2 provokes a decline in progesterone secretion around Day 13 by first decreasing the supply of cholesterol to P450_scc.