Effect of progesterone, triiodothyronine and metabolic inhibitors on prolactin stimulated lipid synthesis in goat mammary explants.

The effect of progesterone, 3,3',5-triiodo-L-thyronine (L-T3) and of inhibitors of DNA, RNA and protein synthesis on prolactin stimulated total lipid synthesis in goat mammary explants were studied. Prolactin stimulated lipid synthesis was not affected by the addition of progesterone. The synthesis of lipids in the presence of insulin, cortisol and prolactin was not stimulated by L-T3 (10(-9) mol 1(-1)) added at start of culture. However, when the addition of L-T3 was delayed by 48 h following culture with insulin, cortisol and prolactin, the synthesis of lipids was increased between 96--99 h of culture by 48%. This effect of L-T3 was blocked by the inhibition of RNA synthesis with actinomycin D. The inhibition of DNA synthesis by hydroxyurea or cytosine-arabinofuranoside had no effect on prolactin stimulated lipid synthesis in goat mammary explants. Actinomycin D, cycloheximide and puromycin completely blocked prolactin stimulated lipid synthesis when added to culture medium simultaneously with prolactin.