Nature 245, 330 - 332 (12 October 1973); doi:10.1038/245330a0

Prolactin Secretion is Specifically Inhibited by Nickel

FRANK S. LABELLA, RAM DULAR, PETER LEMON, STANLEY VIVIAN & GARY QUEEN

Department of Pharmacology and Therapeutics, University of Manitoba, Faculty of Medicine, Winnipeg, Manitoba, Canada R3E OW3

PROLACTIN (PRL) secretion from the mammalian anterior pituitary gland is apparently chiefly under hypothalamic tonic inhibition in contrast to the primarily stimulatory influence of the brain on the other trophic hormones¹. Extracts of mammalian hypothalamus inhibit the release of PRL in vitro and in vivo ¹. We report here that PRL-inhibiting-factor (PIF) activity in certain fractions derived from acetic acid extracts of bovine hypothalamus was due to nickel ion (Ni²⁺) in the extracts. Commercial nickel salts and purified PIF from bovine brain specifically inhibit release of PRL in vivo in the rat and in vitro from bovine pituitary, (a) in basal conditions, (b) in the presence of copper ion which markedly enhances release of all trophic hormones, and (c) following brief exposure of the pituitary tissue to cold, another effective, non-specific stimulant of hormone release.

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