Elsasser T H, Rumsey T S, Kahl S
U.S. Department of Agriculture, Ruminant Nutrition Laboratory, Beltsville, MD 20705.
Domest Anim Endocrinol. 1993 Apr;10(2):71-85. doi: 10.1016/0739-7240(93)90013-2.
Three studies assessed the effect of thyroid status on regulation of plasma IGF-I in cattle. First, four Angus-Hereford steers (av wt 345 kg) were fed 4 mg/d propylthiouracil daily for 35 d. With continued feeding of PTU steers were sequentially injected with thyroxine (T4, 5 mg/d, IM for 5 d) followed by triiodothyronine (T3, 2 mg/d, IM for 5 d). An injection of bovine pituitary growth hormone (GH, 0.1 mg/kg, IM) was given to each steer on day 35 of PTU, day 5 of T4 and again on day 5 of T3. PTU alone increased plasma thyroid stimulating hormone (TSH), decreased plasma T4 and T3 but had no influence on IGF-I. T3, but not T4, lowered plasma TSH, IGF-I and the IGF-I response to GH (P < .05). Next, twelve bull calves (av wht 167 kg) were divided equally into two groups. A control group was injected daily for five d with buffered saline; the experimental group was concurrently treated with T3 (5 mg/d, sc) for five d. Beginning the sixth day, all calves were injected with GH (0.1 mg/kg, IM daily) for three d with the respective buffer or T3 treatments continuing. Plasma IGF-I was depressed 29% by T3. The incremental area under the three-d response curve was less (P < .03) in T3 cattle. A growth trial was conducted in which twenty-four Angus x Hereford steers were injected daily with T3 (2 mg/kg, bi-daily x 56 d) or implanted with Synovex-S (S) in a 2 x 2 factorial arrangement. Synovex increased empty body protein gain (EBPG) and plasma IGF-I 15.5 and 27.9% (P < .01), respectively; T3 decreased EBPG and plasma IGF-I 13.9 and 15.1% (P < .07), respectively, in steers which maintained suppression in plasma TSH. The data support the conclusion that elevated T3 decreases plasma IGF-I, in part, through a diminished GH-responsiveness and anabolic treatments such as S can reverse the effects of excess T3.
三项研究评估了甲状腺状态对牛血浆胰岛素样生长因子-I（IGF-I）调节的影响。首先，给4头安格斯-赫里福德阉牛（平均体重345千克）每天饲喂4毫克丙硫氧嘧啶，持续35天。在持续饲喂丙硫氧嘧啶的过程中，依次给阉牛注射甲状腺素（T4，5毫克/天，肌肉注射，共5天），随后注射三碘甲状腺原氨酸（T3，2毫克/天，肌肉注射，共5天）。在丙硫氧嘧啶处理的第35天、T4处理的第5天以及T3处理的第5天，给每头阉牛注射一次牛垂体生长激素（GH，0.1毫克/千克，肌肉注射）。单独使用丙硫氧嘧啶会使血浆促甲状腺激素（TSH）升高，血浆T4和T3降低，但对IGF-I没有影响。T3而非T4降低了血浆TSH、IGF-I以及IGF-I对GH的反应（P < 0.05）。接下来，将12头公牛犊（平均体重167千克）平均分为两组。对照组每天注射5天缓冲盐水；实验组同时用T3（5毫克/天，皮下注射）处理5天。从第6天开始，所有牛犊每天注射GH（0.1毫克/千克，肌肉注射），共3天，同时继续各自的缓冲液或T3处理。T3使血浆IGF-I降低了29%。T3处理的牛在三天反应曲线下的增量面积更小（P < 0.03）。进行了一项生长试验，将24头安格斯×赫里福德阉牛按2×2析因设计，每天注射T3（2毫克/千克，每日两次，共56天）或植入司诺威辛-S（S）。司诺威辛使空体蛋白增加（EBPG）和血浆IGF-I分别增加了15.5%和27.9%（P < 0.01）；在血浆TSH维持抑制状态的阉牛中，T3分别使EBPG和血浆IGF-I降低了13.9%和15.1%（P < 0.07）。这些数据支持以下结论：T3升高会部分通过降低GH反应性来降低血浆IGF-I，而诸如司诺威辛这样的合成代谢处理可以逆转过量T3的影响。
