RAT PROLACTIN SYNTHESIS BY LACTATING MAMMARY EPITHELIAL-CELLS

It has previously been suggested that the mammary cell could produce p rolactin (PRL). This hypothesis was investigated by incubation with [S -35]methionine-cysteine followed by SDS-PAGE, immunoblotting and autor adiography of immunoprecipitated PRL, and by electron microscopic anal ysis after incubation without or with cycloheximide. Immunoreactive 14 -, 23-, 25-, 32 and 36-kDa PRL forms mere radioactive, By two-dimensio nal electrophoresis analysis, immunoreactive and radioactive spots, of about 25 kDa and high molecular weight, were also detected, After inc ubation of mammary epithelial cells with cycloheximide, immunogold ele ctron microscopy showed a drastic decrease of labelling in organelles involved in synthesis and secretion, compared to those incubated in co ntrol medium, These results make it possible to conclude that lactatin g mammary tissue is able to synthesize PRL.