Biomedical subjects
Publications and source records attributed to T Antakly.
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The effects of incubation of rat anterior pituitary cells in monolayer culture with 10(-6) M colchicine have been investigated during time-intervals extending from 1 to 96 hours. Prolactin release, as measured by radioimmunoassay, was rapidly inhibited by colchicine, this inhibition being accompanied by increased cellular prolactin content for up to 24 hours of treatment and followed by decreased values of cellular prolactin concentration at later time-intervals. Immunocytochemical localization showed an increased positive reaction for prolactin up to 24 hours after colchicine treatment, whereas transmission electron microscopy demonstrated, in parallel, an increased number of intracellular prolactin secretory granules during the same interval. Longer periods of treatment (24-96 hours) resulted in the appearance of more lysosomes, autophagic vacuoles and microfilaments in the cells, whereas the number of Golgi elements was decreased. Following four hours of colchicine treatment and at later stages, microtubules could no longer be observed in the sections. Scanning electron microscopic data showed that colchicine treatment induced dramatic changes in the cell surface morphology: at short time intervals (4 and 8 hours), the number of microvilli decreased and the cell surface became folded, whereas, later, "bleb"-like protrusions of variable dimensions partially covered the cell surface and seemed to be released from it. These data show a good correlation between secretory activity of prolactin-producing cells and morphological changes induced by colchicine treatment.
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A novel peptide hormone, atrial natriuretic factor (ANF), was recently isolated and characterized in mammalian atria. This hormone has potent natriuretic diuretic and vasorelaxant activities. Since ANF bioactivity was initially found in atria but not in ventricles, it was assumed that the ANF gene is specifically expressed in atria. We now report that ANF mRNA is present in ventricular tissue as well as in atria. This is clearly demonstrated by in situ hybridization and by Northern blot analysis. Rat ventricular ANF mRNA concentration is a hundred-fold lower than in atria. As in atria, the 126 amino acids precursor form of ANF is predominant in ventricles and it is present at a thousand-fold lower concentration. The ten-fold discrepancy in the ratio of ANF mRNA to immunoreactivity between atria and ventricles could reflect a higher rate of peptide release in the latter. Thus, ventricular ANF production may be physiologically significant in view of the much larger ventricular mass.