Direct Suppression by β-Mercaptoethanol of the Prolactin Immunoreactivity Within the Cultured Rat Adenohypophyseal Cells

Effects of beta-mercaptoethanol (ME) on the hormonal dynamics of immunoreactive prolactin (iPRL) were examined, using rat adenohypophyseal cells in primary culture. ME caused a rapid onset (within 2-9 min) of dose- and time-dependent reduction in the secretion and intracellular content of iPRL through some reversible process(es). These effects were observed under basal condition, as well as during stimulation with vasoactive intestinal peptide (VIP). The minimum effective doses of ME ranged from 0.0001 to 0.01%. Higher doses caused up to 86-98% reduction of medium or intracellular contents of iPRL compared to the control treatments. When cell lysates and media collected from ME-free cultures were incubated with ME in the test tubes, however, only intracellular iPRL was reduced. Gel filtration profiles showed that ME markedly decreased monomeric form of iPRL with a concomitant increase in the higher molecular weight form(s), presumably oligomers. These results suggested that ME acted directly on the PRL molecules within the cells, causing oligomerization of iPRL via thiol-disulfide interchange. Such molecular transformation might play an important role in the physiological regulation of secretion and storage of iPRL.

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