Responses of mouse mammary gland casein mRNA to corticosteroid action and suckling

Abstract

The consequence of adrenalectomy and cortisol treatment on lactating mammary gland polysomes and RNA to direct casein (determined by specific immunoprecipitation) synthesis in homologous (mammary ribosomes) and heterologous (ascites ribosomes) cell-free protein synthesis systems was assessed. Adrenalectomy-induced virtual loss of larger polysomes was accompanied by a corresponding reduction of in vitro casein synthesizing activity of the ribosomal aggregates of postpartum mammary cells and cortisol treatment prevented this adverse response. Adrenalectomy of lactating mothers also caused a 85–92% reduction of casein mRNA activity in phenol-chloroform extracted mammary RNA and this loss was preventable by cortisol treatment of the nursing mothers. After sodium dodecyl sulfite (SDS) polyacrylamide gel electrophoresis the predominantly synthesized polypeptide(s) both in the acid-insolble and the immunoprecipitable materials in the cell-free reaction product migrated in close correspondence with peak 3 of the milk proteins. The results demonstrate that the glucocorticoid is needed to maintain the high level of the mRNA for the milk protein in the postpartum mammary gland and responses of the polysomes may reflect the modulating action of the glucocoiticoid on the mRNA itself. It was also observed that intensity of suckling influences the functional casein mRNA population in the mammary gland of nursing mothers.