Glucocorticoid Binding in Mammary Tissue Slices of Cattle in Various Reproductive States

Abstract

Unlabeled cortisol and dexamethasone reduced tritiated cortisol and tritiated dexamethasone binding to 700 X g supernatant and precipitate fractions of mammary tissue slices from virgin heifers and from multiparous cows that were 1-mo prepartum (nonlactating), lactating (non-pregnant), or dry (nonpregnant, nonlactating). Unlabeled progesterone, testosterone, and 17beta-estradiol had no effect on tritiated glucocorticoid binding in 700 X g supernatant and precipitate fractions from these mammary tissue slices. The 700 X g fractions in mammary tissue slices from all cattle bound cortisol and dexamethasone with high affinity (Kd 10-10M). There were 1263 and 1955 molecules of cortisol and dexamethasone bound per mammary cell, respectively, in mammary tissue slices from lactating non-pregnant cows; in comparison virgin heifers bound 413 and 651 molecules of cortisol and dexamethasone; dry, non-pregnant cows bound 336 and 536 molecules of cortisol and dexamethasone; and 1-mo prepartum nonlactating cows bound 532 molecules of cortisol. Mammary tissue slices from cattle in reproductive states examined contained a major non-specific component which bound cortisol in both 700 X g tissue fractions. Since mammary tissue slices from lactating cattle bound more molecules of glucocorticoids than mammary slices from cattle in other reproductive states, we speculate specific glucorticoid binding may be associated with lactation.