Analysis of the direct action of prolactin and steroids on mammary tissue of the dog in organ culture

The induction by exogenous hormones of enzymes metabolising glucose 6-phosphate in the mammary gland of the pseudopregnant rabbit

A study was made of the effects of the hormones, prolactin and cortisol acetate, on the activities in the mammary gland of the pseudopregnant rabbit of the enzymes concerned with lactose biosynthesis and glucose 6-phosphate metabolism, namely: UDP-glucose pyrophosphorylase, UDP-glucose-4'-epimerase, phosphofructokinase, phosphoglucomutase, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Significant increases in enzyme activities were observed in rabbits examined 3 or 4 days after receiving a mammary intraductal injection of prolactin. The activities were not significantly increased at examination 2 days after injection of prolactin. Rabbits receiving cortisol acetate each day for 3 days also showed no significant increases in mammary enzyme activity. However, when prolactin and cortisol acetate were given simultaneously over a period of 3 days, increased enzyme activities were found suggesting synergistic action of the hormones.

Regulation of cortisol uptake in mammary tissue of cows

Mammary tissue explants from four nonlactating, nonpregnant cows were placed into culture with media containing various combinations of insulin, prolactin, growth hormone, 17beta-estradiol, dexamethasone, and progesterone. Combinations of insulin, prolactin, growth hormone, or 17beta-estradiol had no effect on cytoplasmic or nuclear uptake of tritiated cortisol compared with values at zero time. Combinations containing dexamethasone of progesterone reduced cytoplasmic and nuclear uptake of tritiated cortisol. To examine inhibition by progesterone of binding of tritiated cortisol, mammary tissue from each of four lactating, nonpregnant and four nonlactating, nonpregnant cows were placed in flasks containing tissue culture medium 199, tritiated cortisol (2 ng/ml), and progesterone at concentrations of 0, 10(-12), 10(-11), 10(-10), 10(-9), 10(-8), 10(-7), 10(-6), or 10(-5) X 6.4 M. Cytoplasmic uptake of tritiated cortisol into nonlactating tissue decreased linearly as progesterone increased, whereas tritiated cortisol uptake in lactating tissue did not decrease until progesterone exceeded 10(-7) M. We postulated progesterone is sequestered in milk fat of cytoplasm of lactating tissue whereas in nonlactating tissue progesterone is available to compete with cortisol at sites of cortisol binding.