Effects of exogenous cortisol on the uptake of corticosteroid by the isolated perfused guinea-pig mammary gland.

Assay of corticosteroids in the plasma of guinea-pigs showed that concentrations were higher in lactating than in non-lactating and male animals. In five isolated perfused mammary gland experiments in which corticosteroids were at concentrations of 1,3--3,0 microgram/ml in the perfusate, equivalent to concentrations during lactation, the mean (+/- S.E.M.) uptake by the mammary gland was 900 +/- 210 ng g-1 h-1. In five experiments in which the concentrations of corticosteroid in the perfusate were 190--580 ng/ml, the uptake by the mammary gland was significantly lower (316 +/- 73 ng g-1 h-1; P less than 0.05). For the ten experiments there was a significant correlation between the concentration of corticosteroid in the perfusate and uptake by the mammary gland (P less than 0.05). No convincing evidence for a galactopoietic role of corticosteroids in the guinea-pig was obtained, although administration of cortisol signficantly stimulated the uptake of glutamine by the perfused gland.