Lactose synthetase induction by hormones in normal and tumorous GR mouse mammary tissue

To analyse the effect of hormones on protein synthesis in hormone‐induced GR mouse mammary tumors, a comparative study was made of the A and B protein contents of the hormone‐inducible enzyme lactose synthetase (EC 2.4.1.22). The A protein could be induced by estrone and progesterone separately and in combination in mammary glands of ovariectomized mice. Increased amounts were demonstrated during pregnancy, when peak levels were recorded in the lactating gland. A three‐fold increase was found in primary tumors as well as in transplanted hormone‐dependent and independent tumors, as compared to the level in normal mammary tissue. However, no significant difference could be demonstrated between A protein activity in the two types of tumors, and no further increase was observed in animals with independent tumors following hormonal treatment. The B protein could be demonstrated in normal mammary tissue of intact as well as ovariectomized animals. There was a decrease in pregnant animals, while peak values were recorded in lactating animals. A rise in B protein could be induced by estrone in normal mammary tissue. Progesterone blocked the induction. However, no significant level of B protein could be demonstrated in primary tumors or in transplanted hormone‐dependent and ‐independent tumors. Nor was any increase noted in animals with independent tumors after hormone treatment. We conclude that hormonal induction of B protein is repressed in GR mammary tumors. The A protein also is no longer hormone‐inducible, but the level is high compared to that of normal unstimulated mammary gland.