Ontogeny of hepatic bovine growth hormone receptors in cattle.
A series of studies examined the binding characteristics and ontogeny of hepatic growth hormone binding sites in dairy bulls on d 2, 30, 180, and 365 of age. Binding of iodinated recombinant bovine growth hormone ([125I]rbGH) to liver membrane receptors was membrane protein-dependent. Receptors were considered growth hormone-specific, because physiological concentrations of bovine prolactin (bPRL) failed to displace [125I]rbGH from bovine hepatocyte membranes. Only 50% of [125I]rbGH was bound reversibly to hepatic microsomes. Addition of dithiothreitol (DTT) to the receptor-assay buffer increased the binding of [125I]rbGH to hepatic membranes in a time-dependent manner. Moderate concentrations of Ca++ and Mg++ in the receptor-assay buffer had no detectable effects on binding of [125I]rbGH to hepatic microsomes. In growing dairy bulls, specific binding of [125I]rbGH per milligram of membrane protein increased from 1.9 +/- 1.8% at d 2 to 14.1 +/- 1.8% at d 180 and then declined to 5.2 +/- 1.6% at d 365. Likewise, concentration of insulin-like growth factor (IGF)-I in serum was low during the 1st mo of age (d 2, 13.3 +/- 8.8 ng/ml; d 30, 9.7 +/- 8.8 ng/ml), but it became maximal at d 180 (151.0 +/- 8.8 ng/ml). Circulating concentrations of IGF-II increased linearly during the 1st yr of growth. Serum concentrations of GH, triiodothyronine, and thyroxine declined from 39.9 +/- 6.5, 2.7 +/- .2, and 75.4 +/- 4.6 ng/ml at d 2 to 16.5 +/- 6.5, 1.3 +/- .2, and 53.4 +/- 4.6 ng/ml at d 30, respectively, and remained low through 1 yr of age. Insulin concentration in serum did not change significantly with development. Results indicated that increasing concentrations of specific bGH receptors in the bovine liver may play a key role in regulating postnatal growth in cattle.
Badinga
L
L
Dairy Sci. Dept., University of Florida, Gainesville 32611.
Collier
R J
RJ
Thatcher
W W
WW
Wilcox
C J
CJ
Head
H H
HH
Bazer
F W
FW
D000375:Aging / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002417:Cattle / Q000254:growth & development*; D004229:Dithiothreitol / Q000494:pharmacology; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D007335:Insulin-Like Growth Factor II / Q000032:analysis; D016018:Least-Squares Analysis; D008099:Liver / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism; D011986:Receptors, Somatotropin / Q000032:analysis*; D011994:Recombinant Proteins / Q000378:metabolism; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D007328:Insulin; D011986:Receptors, Somatotropin; D011994:Recombinant Proteins; D014284:Triiodothyronine; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D011388:Prolactin; D013006:Growth Hormone; D013974:Thyroxine; D004229:Dithiothreitol