Biochemical changes during development of mouse mammary tissue in organ culture

A study has been made of the metabolism of mammary tissue from midpregnant C3H mice in organ culture, with and without the hormones needed to induce lactogenesis in the tissue. Insulin greatly stimulated the uptake of glucose by the tissue, and the formation of labelled carbon dioxide and fatty acids from labelled glucose. The further addition of prolactin and corticosterone had little effect. Without hormones the rates of incorporation of [3H]thymidine into DNA and of [14C]uridine into RNA decreased during culture. Insulin stimulated these rates of incorporation and the further addition of prolactin stimulated them still more. Corticosterone had little effect. The rate of incorporation of [32P]orthophosphate into casein fell during culture without added hormones, while insulin, or insulin plus corticosterone, had little effect on it. Prolactin, however, caused a very marked stimulation in cultures with insulin, which was only slightly increased by the further addition of corticosterone. The stimulation of 32P incorporation due to prolactin was only evident after 12 hr. of culture. Delay in addition of prolactin by 12 hr. did not affect the response. Actinomycin D, cycloheximide and colchicine prevented the action of prolactin; hydroxyurea partly prevented it.

Increase in activity of glucose 6-phosphate dehydrogenase in mouse mammary tissue cultured in insulin

1. In organ cultures of mammary tissue from C3H mice we observed increases in the activity of glucose 6-phosphate dehydrogenase similar to that occurring at parturition. 2. In 22hr. cultures of tissue from late-pregnant mice insulin was required for the increases, but the further addition of prolactin, corticosterone and certain other hormones had no effect. The rise in activity occurred over the second half of the culture period. 3. Results from culture of adipose tissue, and mammary tissue rich in adipose tissue, strongly suggest that the rise in activity occurs in mammary parenchymal rather than adipose cells. 4. In 45hr. cultures prolactin prevented a fall in enzyme activity between 22hr. and 45hr. If the medium contained serum the activity at 22hr. was unaffected, but it continued to rise up to 45hr., and prolactin then had no effect. 5. The enzyme also increased in activity in cultures of mammary tissue from mid-pregnant mice. Insulin was again required, the activity was higher at 45hr. than at 24hr. and prolactin increased the activities at both these times. 6. Actinomycin D, cycloheximide and puromycin at low concentration in the media of 22hr. cultures all prevented increases in enzyme activity. Hydroxyurea at a concentration that inhibited the incorporation of [(3)H]thymidine into DNA by 92% had little effect. 7. Actinomycin D and cycloheximide largely failed to prevent the rise in enzyme activity if added after 3.5hr. and 12hr. respectively. Hence all essential RNA and protein synthesis appears to be finished by 3.5hr. and 12hr., although most of the increase in enzyme activity occurs gradually between 12hr. and 22hr. 8. We suggest that the increases in enzyme activity, both in culture and in the living animal at parturition, are induced by an influx of glucose that is restrained during pregnancy by the growth-hormone-like action of placental lactogen.

Stimulation by hormones of RNA and protein formation in organ cultures of the mammary glands of pregnant mice

Explants of the mammary glands of 11–13 day pregnant C3H mice have been cultured in a synthetic medium with hormone additions. In cultures with insulin and corticosterone the lumina of mammary alveoli became enlarged by 48 hr. but contained little or no visible secretion; alveolar cells were not vacuolated. The rate of incorporation of [14C]adenine into RNA, and the RNA content of these explants, had fallen by 48 hr. In cultures with insulin, corticosterone and prolactin, secretion was already present in the enlarged alveolar lumina by 24 hr. and had increased in amount by 48 hr. Many alveolar cells contained secretory vacuoles. The rate of incorporation of [14C]adenine into RNA had nearly doubled by 24 hr., and the RNA content of the explants had also increased. These increases were still evident at 48 hr. The rate of incorporation of [14C]adenine into RNA was also measured at 3-hr. intervals up to 12 hr. With insulin alone, the rate remained roughly constant over the 12 hr. With insulin, corticosterone and prolactin it began to rise after 6 hr. and was finally about twice the initial value. The rate also rose to a lesser extent after 6 hr. with insulin and corticosterone. After 12 hr. with insulin, corticosterone and prolactin the rate of incorporation of [14C]lysine into proteins was also higher than with insulin alone.