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Seasonal Variation of Neuropeptide Y Actions on Growth Hormone and Gonadotropin‐ll Secretion in the Goldfish: Effects of Sex Steroids
Author(s) -
Peng Chun,
Trudeau Vance L.,
Peter Richard E.
Publication year - 1993
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.1993.tb00483.x
Subject(s) - medicine , endocrinology , neuropeptide y receptor , gonadotropin , testosterone (patch) , hormone , biology , neuropeptide , chemistry , receptor
The effects of neuropeptide Y (NPY) on growth hormone (GH) and gonadotropin‐II (GtH‐II) release in different reproductive stages were studied using perfused pituitary fragments of female goldfish. The GH and GtH‐II release responses to 5‐min pulses of NPY were relatively small in sexually regressed fish (July), intermediate in recrudescent fish (December), and maximal in sexually mature (= prespawning) fish (May). To test if sex steroids can modulate NPY action, the effects of in vivo implantation of 17β‐estradiol (E 2 ) and testosterone (T) (both at 100 μg/g dosage) on NPY‐induced GH and GtH‐II secretion were examined. In sexually regressed goldfish, implantation of T significantly enhanced NPY‐induced GH and GtH‐ll release from perfused pituitary fragments; implantation of E 2 potentiated the NPY‐induced GtH‐II, but not GH release. However, steroid implantation did not affect responses to NPY when this experiment was repeated using pituitaries from sexually mature fish. To test the hypothesis that steroids may act directly at the level of the pituitary to potentiate NPY action, pituitary fragments taken from sexually regressed goldfish were incubated with 100 nM T for 24 h, and the GH and GtH‐ll responses to 5‐min challenges of NPY assessed in the presence of T. Both GH and GtH‐ll responses to NPY were not affected by treatment with T in vitro , suggesting that T does not act directly at the level of the pituitary. Since we have found that gonadotropin‐releasing hormone (GnRH) in part mediates the effects of NPY on GH and GtH‐ll release, the possibility that steroids may potentiate the actions of NPY on GnRH release were also examined. In sexually regressed fish, NPY did not alter GnRH release either from pituitary fragments or preoptic anterior hypothalamic slices. When fish were pretreated with E 2 and T by in vivo implantation, NPY significantly stimulated the release of GnRH. Taken together, these results demonstrate that: 1) there is a seasonal variation of NPY action on GH and GtH‐ll release in the female goldfish; 2) sex steroids, especially T, potentiate the effects of NPY on GH and GtH‐ll release in sexually regressed fish, when the endogenous steroid levels are low; and 3) the seasonality of NPY actions and the potentiation by steroids may be mediated, at least in part, by enhanced stimulation of GnRH release.