THE ASYNCHRONOUS HORMONAL INDUCTION OF LACTOSE SYNTHETASE COMPONENTS, α-LACTALBUMIN AND GALACTOSYLTRANSFERASE, IN RELATION TO LACTOSE SECRETION BY MOUSE MAMMARY EXPLANTS

Publisher Website
Google Scholar
Abstract
Hormonal induction of the lactose synthetase components, α-lactalbumin and galactosyltransferase, in relation to the induced levels of lactose synthetase activity and lactose secretion by mammary gland explants from mature virgin mice was examined. During 6 days of culture in the presence of insulin, cortisol, prolactin and triiodothyronine mammary explants accumulated progressively increasing amounts of α-lactalbumin. By contrast, galactosyltransferase and lactose synthetase activities were maximal on day 3, and then declined; the time course of lactose secretion was similar to that of galactosyltransferase and lactose synthetase activities. Cortisol concentration studies revealed the following dependencies on the steroid: α-lactalbumin content was maximal between 0.01 and 0.1 μg/ml and, at 10 μg/ml fell below the baseline level observed without cortisol. On the other hand, galactosyltransferase, lactose synthetase and lactose secretion were only slightly increased at 0.01 μg/ml, were maximal between 0.1 and 1.0 μg/ml, and at 10 μg/ml were still considerably above the baseline levels observed without cortisol. These results indicate that lactose formation and secretion by mammary explants from virgin mice correspond more closely to the hormone-induced activity of galactosyltransferase than to that of α-lactalbumin, and that asynchrony can arise between the induction of α-lactalbumin and the induction of lactose.