Progesterone inhibition of glucocorticoid binding to mammary tissue from lactating and nonlactating cows.

Abstract

AbstractMammary tissue cytosols (105,000g supernatants) were prepared from lactating or from nonlactating, nonpregnant cows, then incubated with [3H]dexamethasone alone (3 × 10-8M) or in combination with various unlabeled hormones (1.9 × 10-7 or 1.9 × 10-6M). Cortisol, corticosterone, and progesterone inhibited binding of [3H]dexamethasone, whereas testosterone, cortisone, and estradiol-17 β did not. Binding affinities of mammary cytosols from lactating and nonlactating cows for [3H]dexamethasone (0.5 to 100 nM) were virtually identical averaging 1.4 (± 0.3) and 2.0 (± 1.2) × 10-9M, respectively. However, binding capacities of mammary tissue slices (fmole dexamethasone/μg DNA) were greater in lactating (2.3) than in nonlactating (1.5) cows. Specific cytosolic binding sites sedimented at 8 and 4 S on sucrose gradients. Whole mammary slices were incubated with 3 × 10-9M [3H]dexamethasone alone or in combination with 10-13 to 10-5 × 3.8 M progesterone or 3 × 10-7M dexamethasone, and cytoplasmic and nuclear f...