Interplay between estradiol and prolactin in the regulation of steroid hormone receptor levels, nature, and functionality in normal mouse mammary tissue.

Abstract

Under different experimental conditions, normal mouse mammary tissue can be shown to contain molecular species of cytoplasmic estrogen receptors which differ in their physicochemical properties and kinetic behavior with respect to estradiol binding. The relative capabilities of PRL and estradiol to effect molecular interconversion of these receptor forms have been examined. Chronic administration of estradiol to a mature virgin mouse increases nuclear receptor levels 5-fold and converts cytoplasmic receptors from a 4S to an 8S form. PRL has an even greater augmentative effect on cellular receptor content, also causing 4S to 8S conversion, but is much less effective than estradiol in elevating nuclear receptor levels. CB-154, which blocks PRL production, totally inhibits estrogen promotion of specific binding activity, while partially permitting 8S cytoplasmic receptor formation. Short term administration of estradiol to a mouse in late pregnancy (all cytosol receptor in the 8S form) causes a cytosol to nu...