Abstract
Summary
Incubation of anterior pituitary glands of female rats with 10-5 M vincristine or colchicine reduced both synthesis and release of prolactin. Incubation of glands of perphenazine-treated male rats with 10-5 M colchicine or vincristine blocked the perphenazine-induced increase in in vitro prolactin synthesis. At 10-4 M, vincristine inhibited synthesis and release of growth hormone by glands of untreated male rats but could not block the dibutyryl cyclic AMP-induced stimulation of growth hormone release. Incubation of glands of male rats with 10 μg/ml cytochalasin B resulted in decreased growth hormone synthesis. Incubation of glands of female rats with the drug significantly decreased synthesis and release of both prolactin and growth hormone. Concomitant electron microscopic observations indicated that cytoplasmic microtubules are uncommon in the pituitary gland and that they are still present after glands were treated with vincristine and colchicine at doses capable of inhibiting prolactin release. For this reason and because no binding of radioactive colchicine to pituitary glands occurred in vitro, it is suggested that microtubules are not significantly involved in prolactin and growth hormone secretion.
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