Badinga L, Collier R J, Thatcher W W, Wilcox C J, Head H H, Bazer F W
Dairy Sci. Dept., University of Florida, Gainesville 32611.
J Anim Sci. 1991 May;69(5):1925-34. doi: 10.2527/1991.6951925x.
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.
一系列研究检测了不同年龄（2日龄、30日龄、180日龄和365日龄）的奶牛公牛肝脏生长激素结合位点的结合特性和个体发生情况。碘化重组牛生长激素（[125I]rbGH）与肝细胞膜受体的结合依赖于膜蛋白。受体被认为是生长激素特异性的，因为生理浓度的牛催乳素（bPRL）无法从牛肝细胞膜上取代[125I]rbGH。只有50%的[125I]rbGH可逆地结合到肝微粒体上。在受体测定缓冲液中添加二硫苏糖醇（DTT）可使[125I]rbGH与肝细胞膜的结合呈时间依赖性增加。受体测定缓冲液中适度浓度的Ca++和Mg++对[125I]rbGH与肝微粒体的结合没有可检测到的影响。在生长中的奶牛公牛中，每毫克膜蛋白的[125I]rbGH特异性结合从2日龄时的1.9±1.8%增加到180日龄时的14.1±1.8%，然后在365日龄时下降到5.2±1.6%。同样，血清中胰岛素样生长因子（IGF）-I的浓度在1月龄时较低（2日龄时为13.3±8.8 ng/ml；30日龄时为9.7±8.8 ng/ml），但在180日龄时达到最高（151.0±8.8 ng/ml）。IGF-II的循环浓度在生长的第1年呈线性增加。血清中生长激素、三碘甲状腺原氨酸和甲状腺素的浓度分别从2日龄时的39.9±6.5、2.7±0.2和75.4±4.6 ng/ml下降到30日龄时的16.5±6.5、1.3±0.2和53.4±4.6 ng/ml，并在1岁时一直保持较低水平。血清胰岛素浓度随发育没有显著变化。结果表明，牛肝脏中特异性bGH受体浓度的增加可能在调节牛出生后的生长中起关键作用。
