EFFECTS OF COLCHICINE ON THE MORPHOLOGY AND PROLACTIN SECRETION OF RAT ANTERIOR-PITUITARY CELLS IN MONOLAYER-CULTURE

The effects of incubation of rat anterior pituitary cells in monolayer culture with 10-6 M colchicine were studied during time-intervals extending from 1-96 h. Prolactin release, as measured by radioimmunoassay, was rapidly inhibited by colchicine; this inhibition was accompanied by increased cellular prolactin content for up to 24 h 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 h after colchicine treatment, but transmission electron microscopy showed, in parallel, an increased number of intracellular prolactin secretory granules during the same interval. Longer periods of treatment (24-96 h) caused the appearance of more lysosomes, autophagic vacuoles and microfilaments in the cells, but the number of Golgi elements was decreased. After 4 h of colchicine treatment and at later stages, microtubules could no longer be seen in the sections. Scanning electron microscopic data showed that colchine treatment induced dramatic changes in the cell surface morphology. At short time intervals (4 and 8 h), the number of microvilli decreased and the cell surface became folded, but later, bleb-like protrusions of variable dimensions partially covered the cell surface and seemed to be released from it. Good correlation was shown between secretory activity of prolactin-producing cells and morphological changes induced by colchicine treatment.