Secretory Morphology Research Articles

Mammary explants from midpregnant mice were cultured for up to 96 hr with various combinations of insulin, prolactin, and corticosterone. Labeled glucose was added to cultures at 4 hr prior to termination, and explant morphology, glucose uptake, and lipid synthesis were studied in hormone-free and hormone-containing media. The results show that without hormones, explants take up glucose and synthesize lipid at minimal rates. After 48 hr these activities appear to be primarily those of adipose tissue since epithelial and connective tissue degenerate without hormones. Insulin increases cell number for 24 hr and maintains survival for 96 hr. Its stimulatory effect on lipogenesis precedes its enhancement of glucose uptake. The addition of prolactin to insulin-containing cultures has little effect on glucose uptake and lipogenesis, but stimulates minimal secretion in alveolar lumina. The absence of intracellular vacuoles indicates that these products probably contain little lipid. Corticosterone enhances the effects of insulin on lipid synthesis, but has little apparent effect on the secretory morphology of the alveoli. The three-hormone combination has no effect on glucose uptake above that obtained with insulin alone; however, it induces marked increases in Iipid synthesis as well as maximal morphological secretion by 48 hr. Thus, as for other lactogenic responses in vitro, insulin, prolactin, and corticosterone act synergistically to stimulate lipid synthesis in mammary explants.

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