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The Acid-Labile Subunit Is Required for Full Effects of Exogenous Growth Hormone on Growth and Carbohydrate Metabolism

Department of Animal Science (I.U., S.L.G., K.J.H., Y.R.B.), Cornell University, Ithaca, New York 14853; and Division of Applied Life Sciences (J.W.K.), Institute of Agriculture and Life Sciences, Gyeongsang National University, Jinju 660-701, Korea

Address all correspondence and requests for reprints to: Yves Boisclair, Department of Animal Science, 259 Morrison Hall, Ithaca, New York 14853. E-mail: yrb1{at}cornell.edu.

Normal postnatal growth is dependent in part on overlapping actions of GH and IGF-I. These actions reflect GH stimulation of IGF-I production in liver and extrahepatic tissues, representing respectively the endocrine and autocrine/paracrine arms of the IGF system. Recent experiments in genetically modified mice show that each source of IGF-I can compensate for absence of the other but do not resolve their relative role in postnatal growth. In an effort to address this issue, we studied the GH responsiveness of mice harboring a null mutation of the acid-labile subunit (ALS). Null ALS mice have a substantial reduction in endocrine IGF-I but, unlike other models of plasma IGF-I deficiency, have no obvious additional endocrine defects. Wild type and null ALS mice of both sexes received daily sc injections of saline or recombinant bovine GH between d 35 and 63 of postnatal age. The GH-stimulated body weight gain of null ALS mice was reduced by more than 30% relative to wild type mice, irrespective of sex. Reductions in GH responsiveness were also seen for kidney and linear growth. Absence of ALS eliminated the ability of GH to increase plasma IGF-I despite intact GH-dependent stimulation of IGF-I expression in liver, adipose tissue, and skeletal muscle. GH treatment was also less efficient in antagonizing insulin action in null ALS mice. Overall, these results suggest that the GH effects mediated by endocrine IGF-I depends on ALS, and accordingly null ALS mice are less responsive to exogenous GH therapy.