Growth regulation in the gobiid teleost Gillichthys mirabilis roles of growth hormone hepatic growth hormone receptors and insulin-like growth factor-I

Abstract:  Growth regulation in the gobiid teleost, Gillichthys mirabilis: roles of growth hormone, hepatic growth hormone receptors and insulin-like growth factor-I. Gray ES, Kelley KM. Department of Integrative Biology, University of California, Berkeley 94720. Studies of the teleost Gillichthys mirabilis were undertaken to assess the role of GH in regulating hepatic GH receptors, insulin-like growth factor-I (IGF-I) activity and cartilage growth. Hypophysectomized G. mirabilis were injected with saline vehicle or with 10, 100 or 1000 ng tilapia GH (tGH)/g every other day for 2-3 weeks. Growth, judged by increased body weight and length, was inhibited by hypophysectomy and stimulated by increasing tGH doses. Hepatic GH receptors, measured by 125I-labelled tGH binding, were decreased 50% by hypophysectomy. An additional dose-dependent reduction in binding was observed 24 h after tGH injection, but MgCl2 stripping of membranes suggested receptor occupation by exogenous tGH. IGF-I activity, measured by 35SO4 incorporation into oral cartilage explants in vitro, was decreased 50% by hypophysectomy and increased to 200% of intact control levels after injection of 1000 ng tGH/g. In a second experiment, 35SO4 incorporation by oral cartilage from hypophysectomized fish injected with 10, 100 or 1000 ng tGH/g was stimulated to intact control levels. Effects of feeding and tGH injection on in-vitro responsiveness of oral cartilage to recombinant bovine IGF-I (rbIGF-I; 10-1000 ng/ml) were also assessed. Oral cartilage from fed fish showed a parabolic dose-response curve, whereas oral cartilage from starved fish had a lower basal rate of 35SO4 incorporation and a linear dose-response relationship. Oral cartilage from hypophysectomized G. mirabilis showed a significantly attenuated response to rbIGF-I which was restored by tGH injection, suggesting that the GH status of the animal is important for sensitivity of target tissue to IGF-I. Because of its similarity to other vertebrate systems, G. mirabilis presents a good teleost model of growth regulation and of the functions and interactions of GH and IGF-I. PMID: 1744560 [PubMed - indexed for MEDLINE]