Direct Stimulation of Growth Hormone Secretion by Galanin in the Domestic Fowl*

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Abstract
Galanin, a novel peptide originally isolated from porcine intestine, has a wide distribution in the nervous system and is known to enhance the release of growth hormone in mammals, though the mechanism of its actions is still subject to debate. In the current study, the effects of galanin on growth hormone secretion in the domestic fowl were investigated. Intravenous injections of galanin into both 8‐week old and 18‐week old female Hubbard broilers produced marked increases in plasma growth hormone, similar in magnitude to that evoked by human growth hormone‐releasing factor. Galanin produced dose‐related increases in growth hormone release, with a peak response occurring within 10 min of administration. Growth hormone release in response to a maximal challenge of growth hormone‐releasing factor was further augmented when galanin was given at the same time. Galanin stimulated growth hormone release from chick hemipituitary glands in vitro, a response which was not dependent upon hypothalamic input. In addition, galanin potentiated the actions of growth hormone‐releasing factor on growth hormone release in vitro and these responses were reversed by somatostatin. These results show that galanin is able to stimulate growth hormone release in the domestic fowl by acting directly on the pituitary gland.