The influence of exogenous oxytoxin on labelling of secretory epithelium of mouse mammary gland by [3H]leucine, evidenced by autoradiography.

Abstract

It has been suggested that oxytocin, besides its milk-ejecting activity, is also involved in the hormonal regulation of the mammary gland secretory cells. The available data, however, are conflicting. In this study two independent experiments, separated by a certain time interval show that oxytocin intravenously administered to mice at days 10-14 of lactation diminished the incorporation of [3H]leucine into the mammary gland tissue by 32 and 53 per cent, respectively. The neurohormone was co-injected with the tracer amino acid. The radioactivity taken up by the secretory cells was estimated by light microscopic autoradiography. The autoradiograms were evaluated by visual silver grain counting. Tissue radioactivity was measured by liquid scintillation counting. A milk stasis in the mammary gland induced by depriving the mice of suckling two hours before tracer injection had no influence on the secretory activity of the glandular cells. It is assumed that oxytocin has a direct effect on the milk-producing cells, and that the reduction in measurable radioactivity caused by the neurohormone may be due to an accelerated intracellular passage of labelled milk proteins.