title: Effect of circulating growth hormone on muscle IGF-I protein concentration in female mice with growth hormone receptor gene disruption.
abstract: Growth hormone (GH) is a potent secretague for circulating insulin-like growth factor-I (IGF-I). The purpose of this study was to examine the effect of circulating GH on muscle IGF-I protein expression using GH transgenic animal models. Three different models were used: mice that overexpress bovine GH (bGH; n=10), mice without a functional GH receptor (GHR-/-; n=10), and wildtype mice (n=10). All mice were 16-week old females and each group differed in their basic phenotypic characteristics. Immediately after euthanization the triceps surae muscle group (soleus, plantaris, and gastrocnemius muscles) was removed. IGF-I was extracted from the muscle with an acid-ethanol solution (12.5% 2N hydrochloric acid and 87.5% ethanol, pH 1.5) followed by neutralization with Tris-base and subsequently quantified using a radioimmunoassay. Analysis revealed that bGH mice had significantly greater muscle IGF-I protein expression compared to GHR-/- and wildtype mice. No difference in IGF-I protein concentration was found between GHR-/- and wildtype animals. This study found that overexpression of GH leading to high circulating GH concentrations increase muscle IGF-I protein expression. However, the absence of a functional GHR did not affect muscle IGF-I protein expression compared to wildtype despite high circulating levels of GH and low circulating levels of IGF-I. In conclusion, it appears that at rest high circulating levels of GH augment muscle IGF-I protein expression only in the presence of an intact GHR but that the absence of a functional GH receptor does not affect basal levels of muscle IGF-I protein in female mice.
authors.affiliation: Department of Kinesiology, University of Connecticut, Storrs, CT 06269-1110, USA. william.kraemer@uconn.edu
authors.forename: William J
authors.initials: WJ
authors.lastname: Kraemer
authors.forename: Jakob L
authors.initials: JL
authors.lastname: Vingren
authors.forename: Mark D
authors.initials: MD
authors.lastname: Schuenke
authors.forename: John J
authors.initials: JJ
authors.lastname: Kopchick
authors.forename: Jeff S
authors.initials: JS
authors.lastname: Volek
authors.forename: Maren S
authors.initials: MS
authors.lastname: Fragala
authors.forename: Keijo
authors.initials: K
authors.lastname: Häkkinen
authors.lastname: Jen-Ho
authors.forename: Gwendolyn A
authors.initials: GA
authors.lastname: Thomas
authors.forename: Robert S
authors.initials: RS
authors.lastname: Staron
mesh_terms: D000818:Animals; D002417:Cattle; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018482:Muscle, Skeletal / Q000378:metabolism*; D011986:Receptors, Somatotropin / Q000502:physiology*
chemical_list: D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone