Analysis of the Direct Action of Prolactin and Steroids on Mammary Tissue of the Dog in Organ Culture

Abstract

Hypotheses by several workers (Meites, Folley, Nandi and Bern) concerning the initiation of milk secretion at the time of parturition have involved the direct action of hormones upon the mammary gland. Initiation of abundant secretion in organ cultures of canine mammary lobuloalveolar tissue has permitted examination of the direct effects of combinations of 17[beta]-estradiol (E), progesterone (P), prolactin (MH) and cortisol (F) on the secretory response in vitro. Synthetic medium 199, supplemented with insulin (5 [mu]g/ml) and containing 50 IU of penicillin G/ml, served as a basal medium for cultured mammary tissue exposed to pituitary, adrenocortical and ovarian hormones. Secretion was stimulated in vitro by 0.1-0.25 [mu]g/ml of MH plus 5 [mu]g/ml of F. These secretory responses could be modified by added ovarian hormones. One to 2 [mu]g/ml of P strongly inhibited secretion, while 1.0 [mu]g/ml of E produced slight inhibition. Tissues exposed to combinations of E and P containing 0.01 [mu]g/ml of P showed slight secretory stimulation, but tissues exposed to other E- and P-containing combinations showed either inhibition or unchanged secretion. High levels of F failed to stimulate further MH-stimulated secretion and possibly failed to overcome E and P inhibitory effects. A mechanism for initiation of lactation is suggested.