Effect of progesterone alone and in combination with either corticosterone, 17 beta-estradiol or insulin on prolactin-stimulated fatty acid synthesis in mammary explants from pseudopregnant rabbits.

Progesterone up to 15.9 mumol/l progressively suppressed prolactin-stimulated fatty acid synthesis in cultured mammary explants from 11-day pseudopregnant rabbits, but did not influence the proportion of fatty acids of medium chain length (C8:0-C12:0). Greater sensitivity to progesterone inhibition was observed at the low end of the ranges of corticosterone (29 nmol/l) and insulin (4.2 nmol/l) concentrations in the culture medium, which suggests an interaction between the hormones. A range of from 0.0001 to 10 mumol/l of 17 beta-estradiol concentrations had no effect on prolactin-stimulated fatty acid synthesis in the presence or absence of progesterone.