The effects of hormones on milk-fat synthesis in mammary explants from pseudopregnant rabbits.

1. When freshly prepared explants from pseudopregnant-rabbit mammary gland were incubated with sodium [1-(14)C]acetate plus glucose, they synthesized triglyceride and phospholipid containing long-chain fatty acids. Explants cultured with insulin and corticosterone also synthesized these products. The addition of prolactin to this culture medium increased the rate of fatty acid synthesis up to 40-fold and the explants synthesized predominantly triglyceride enriched with C(8:0) and C(10:0) fatty acids characteristic of rabbit milk. 2. The maximum rates of fatty acid synthesis obtained by explants from pseudopregnant-rabbit mammary gland after culture with insulin, corticosterone and prolactin were similar to those observed with freshly prepared explants from lactating-rabbit mammary gland. The time in culture required to attain these maximum rates varied between animals, and did not appear to be connected with the time required (6-7 days) to synthesize the maximum proportions of C(8:0) and C(10:0) acids. 3. As the pattern of short- and medium-chain milk fatty acids is characteristic for many species, the techniques described to determine the time-course for the development of this pattern can be used to investigate hormonal response.