Effect of Various Concentrations of Prolactin and Growth Hormone on the Magnitude of Stimulation of RNA Synthesis, Casein Synthesis and Ornithine Decarboxylase Activity in Mouse Mammary Gland Explants

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Abstract
The effects of various concentrations of prolactin and growth hormone on the rates of [3H]-uridine incorporation into RNA, [3H]-leucine incorporation into casein, and ornithine decarboxylase (ODC) activity were determined in mouse mammary gland explants. The lowest concentrations of prolactin which produced significant responses were between 5 and 25 ng/ml. Growth hormone, in contrast, produced significant response at concentrations between 250 and 1,000 ng/ml. The prolactin actions on RNA and casein synthesis were essentially all-or-none type responses, i.e. the magnitude of the responses were maximal at about 10 ng/ml prolactin. The action of prolactin on ODC activity was quite different; a concentration-response relationship was observed with prolactin at concentrations from 10 to 250 ng/ml. It is apparent from these studies that different concentrations of prolactin are required to produce optimal actions on different biochemical parameters in cultured mammary tissues.