CHANGES IN PLASMA LUTEINIZING HORMONE AND PROLACTIN AFTER INJECTION OF VINBLASTINE INTO THE MEDIAN EMINENCE OF THE RAT

Abstract
Colchicine, vinblastine and other tubulin-binding drugs (Borisy & Taylor, 1967; Bensch & Malawista, 1969) are known to block the release of insulin (Lacy, Howell, Young & Fink, 1968), posterior pituitary hormones (Douglas & Sorimachi, 1972), catecholamines (Poisner & Bernstein, 1971) and acetylcholine (Perisic & Cuenod, 1972). This implicates the cytoplasmic microtubule proteins (tubulins) in the mechanism of release of some cell secretory products. The present report presents evidence suggesting that vinblastine injected into the median eminence of female rats produces a prolonged inhibition of the output of luteinizing hormone (LH) releasing hormone and of prolactin inhibiting factor (PIF), thereby affecting gonadotrophin secretion. Holtzman female rats (200 g) showing at least two regular oestrous cycles, were anaesthetized with ether. The injections into the median eminence were performed stereotaxically through a Hamilton syringe with a 27-gauge needle. The experimental animals were injected with 3 μl (1 μl/min) of a 1 mM

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