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

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.

On the role of the peptide galanin in regulation of growth hormone secretion

“…The absence of a stimulatory effect of galanin on soma¬ totropes may be explained by the fact that galanin receptors are not present in the anterior pituitary (22; present results). However, a direct stimulatory effect of galanin on GH release from incubated chicken hemipituitaries has recently been reported (31). Furthermore, the increase in plasma GH levels caused by iv administered galanin to young chickens occurred after the same time as after in¬ fusion of GHRH, suggesting a direct action of ga¬ lanin similar to that of GHRH.…”

The effect of somatostatins (SRIF‐14, 25 and 28), galanin and anti‐SRIF on plasma growth hormone levels in Coho salmon (Oncorhynchus kisutch, Walbaum)

“…However, the magnitude of the G H response was less than that described for homeotherms (cf. Ottlecz et al, 1986;Murakami et al, 1989;Cheung & Hall, 1990). The rapid increase in coho salmon GH noted following delivery of galanin indicates a direct, rather than indirect stimulation of pituitary somatotrophs.…”

“…This peptide's $Author to whom correspondence should be addressed. 887 0022-1 112/92/060887+07 S03.00jO 0 1992 The Fisheries Society of the British Isles physiological activity appears to be related to GH pituitary release, since administration of galanin increases pituitary GH secretion in man (Davis et ul., 1987), rat (Ottlecz et al, 1986;Murakami et al, 1989), and the domestic cock (Cheung & Hall, 1990). Galanin has also been reported to produce a variety of other effects including hyperphagia, inhibition of insulin release and hyperglycemia (Rokaeus, 1987).…”