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Studies were carried out to determine whether the actions of prolactin on the metabolism of the mammary gland may involve polyamines. In mouse mammary gland explants that were preincubated for 2 days with insulin plus hydrocortisone, the rate of [3H]leucine incorporation into casein was enhanced in a prolactin-like manner during a further incubation with spermidine plus cyclic GMP or phospholipase A. Putrescine (0.5 HIM) plus PGF2α, cyclic GMP or arachidonic acid also enhanced the rate of casein synthesis; but PGF2α plus 0.5 mM arginine, ornithine or spermine had no effect. Methyl GAG, an inhibitor of the enzyme S-adenosyl- L-methionine decarboxylase (which is required for the conversion of putrescine to spermidine), abolished the putrescine plus PGF2α stimulation of casein synthesis. Since this drug did not affect the action of spermidine plus PGF2α on casein synthesis, the specific action of spermidine on casein synthesis is suggested. Neither arginine, ornithine nor the polyamines, by themselves, affec...

Lipid biosynthesis in cultured mammary tissues from mice during midpregnancy was maximally stimulated by the combined actions of PRL, insulin, and a glucocorticoid. The minimal concentration of cortisol that was consistently permissive for the action of PRL on lipid synthesis was 0.1 microgram/ml (2.76 X 10(-7) M). The PRL effect began after 6-8 h of exposure to PRL. The response to PRL was essentially all or none, with 25 ng/ml sufficient for maximal stimulation. Specificity of the PRL effect is suggested by the observation that 1 microgram/ml bovine GH was without effect in cultured mammary tissues. Additionally, PRL had no effect on lipid metabolism in explants of ovarian fat pad, suggesting that the PRL effect in the mammary gland is not a generalized effect on fat cells. The action of PRL in the mammary gland requires both ongoing RNA and protein syntheses, since both actinomycin D and puromycin abolished its effect. The early action of PRL on lipid biosynthesis was specific for the formation of triglycerides, but not other lipid classes studied.