Nap R C, Mol J A, Hazewinkel H A
Department of Clinical Sciences of Companion Animals, University of Utrecht, The Netherlands.
Domest Anim Endocrinol. 1993 Jul;10(3):237-47. doi: 10.1016/0739-7240(93)90028-a.
During a 20-week study, 17 Great Dane dogs, 7 weeks of age, were used to study the influence of 3 isoenergetic diets differing in dietary protein levels (i.e., 31.6%, 23.1%, and 14.6% on a dry matter basis) on body weight, growth in length, and age-related plasma GH and IGF levels. Significant differences occurred in weekly body weight gain of the high- and low- protein groups only in the fourth week of the study. There was a significant decrease in mean basal plasma GH values with time from 14.8 +/- 2.2, 13.7 +/- 2.2, and 14.3 +/- 2.2 micrograms/l in the second week to 2.3 +/- 1, 0.7 +/- 0.4, and 1.8 +/- 0.7 microgram/l in the last week of the study for the high-, normal- and low-protein groups, respectively. Differences among groups were not significant. There was a positive correlation between the decrease in weekly body weight gain and plasma GH concentration in all 3 groups. IGF-I concentrations in plasma did not change consistently with age and were not correlated with plasma GH values. Significant differences in plasma IGF-I concentrations were found between groups at 15 weeks of age. Preliminary results of measurements of IGF receptors in the membranes of growth plate cartilage of long bones of 5 dogs revealed that homologous displacement of 125I-labeled IGF-I binding resulted in similar curves. A single binding site for IGF-I was assumed. The large number of type II IGF receptors in 7 dogs suggests a key role for IGF-II in postnatal skeletal growth. The results of this study demonstrate for the first time that in Great Dane pups basal GH concentrations in plasma decrease between 7 and 27 weeks of age, parallel to the decrease in growth velocity, whereas the plasma IGF-I concentrations remain relatively high and unchanged. The slight but statistically significant effects of low-protein feeding on growth velocity and circulating concentrations of IGF-I indicate that a diet containing 14.6% protein on a dry matter basis (13% protein as metabolizable energy) is marginal for growing Great Dane pups between 7 and 17 weeks of age.
在一项为期20周的研究中，选用了17只7周龄的大丹犬，以研究三种等能量日粮（即干物质基础上蛋白质水平分别为31.6%、23.1%和14.6%）对体重、体长生长以及与年龄相关的血浆生长激素（GH）和胰岛素样生长因子（IGF）水平的影响。仅在研究的第四周，高蛋白组和低蛋白组的每周体重增加出现显著差异。随着时间推移，高蛋白组、正常蛋白组和低蛋白组的平均基础血浆GH值从第二周的14.8±2.2、13.7±2.2和14.3±2.2微克/升分别显著降至研究最后一周的2.3±1、0.7±0.4和1.8±0.7微克/升。各组间差异不显著。所有三组的每周体重增加减少与血浆GH浓度之间均呈正相关。血浆中的IGF-I浓度并未随年龄持续变化，且与血浆GH值无关。在15周龄时，各组间血浆IGF-I浓度存在显著差异。对5只犬长骨生长板软骨膜中IGF受体的测量初步结果显示，125I标记IGF-I结合的同源置换产生了相似的曲线。假定存在一个IGF-I的单一结合位点。7只犬中大量的II型IGF受体表明IGF-II在出生后骨骼生长中起关键作用。本研究结果首次表明，在大丹幼犬中，血浆基础GH浓度在7至27周龄之间下降，与生长速度下降平行，而血浆IGF-I浓度保持相对较高且无变化。低蛋白喂养对生长速度和IGF-I循环浓度有轻微但具有统计学意义的影响，这表明干物质基础上含14.6%蛋白质（13%蛋白质作为可代谢能量）的日粮对于7至17周龄生长中的大丹幼犬而言处于边缘水平。
