Effect of circulating growth hormone on muscle IGF-I protein concentration in female mice with growth hormone receptor gene disruption.
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.
Kraemer
William J
WJ
Department of Kinesiology, University of Connecticut, Storrs, CT 06269-1110, USA. william.kraemer@uconn.edu
Vingren
Jakob L
JL
Schuenke
Mark D
MD
Kopchick
John J
JJ
Volek
Jeff S
JS
Fragala
Maren S
MS
Häkkinen
Keijo
K
Jen-Ho
Thomas
Gwendolyn A
GA
Staron
Robert S
RS
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*
D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone