Davis S L, Sasser R G, Thacker D L, Ross R H
Endocrinology. 1977 May;100(5):1394-402. doi: 10.1210/endo-100-5-1394.
Holstein heifers were treated with synthetic thyrotropin-releasing hormone (TRH) or saline twice daily from one week through 6 mo of age. Plasma concentrations of prolactin (PRL) and thyrotropin (TSH) were elevated (P less than .01) within 30 min after the first TRH injection (1 week of age). At 1 and 3 mo of treatment, PRL and TSH increased in response to TRH, although the TSH response was reduced (P less than .01) as compared to the first day of treatment. Although plasma growth hormone (GH) appeared to be elevated following the first TRH injection, this effect was not statistically significant (P less than .05), nor was it significantly influenced by treatment following subsequent TRH injections. None of the 3 hormones, PRL, TSH or GH, was elevated following the final TRH injection at 6 mo of age. In contrast, plasma concentrations of PRL and TSH were increased in a control heifer injected with TRH at 6 mo. These data indicate that hormonal responsiveness to TRH stimulation decreases with continued twice daily treatment at doses of TRH used in the present studies. Examination of weight gains indicated that chronic treatment with TRH was associated with increased growth rate through 6 mo of age (10.6% increased average daily gains P less than .10), which was exhibited in a steeper slope (P less than .05) of the growth curve in the TRH group. Feed intake was slightly greater in TRH heifers, although feed efficiency (kg feed/kg gain) was not different between the two groups. Plasma concentrations of PRL increased (P less than .01) with age (r = +0.938) in control heifers while plasma TSH and GH were not significantly related to age. This observation establishes a positive correlative relationship between PRL secretion and the approach of puberty in the dairly heirfer. It was also noted that elevation of PRL secretion by TRH treatment was associated with significant advancement of age at first observed estrus (9.4 vs. - 10.5 mo) suggesting that a functional relationship between PRL secretion and puberty may exist in dairy heifers.
从1周龄至6月龄，对荷斯坦小母牛每天两次注射合成促甲状腺激素释放激素（TRH）或生理盐水。首次注射TRH（1周龄）后30分钟内，催乳素（PRL）和促甲状腺激素（TSH）的血浆浓度升高（P<0.01）。在治疗1个月和3个月时，PRL和TSH对TRH有反应性升高，尽管与治疗第一天相比，TSH反应降低（P<0.01）。虽然首次注射TRH后血浆生长激素（GH）似乎升高，但这种效应无统计学意义（P<0.05），且后续TRH注射后的治疗对其也无显著影响。6月龄最后一次注射TRH后，PRL、TSH或GH这3种激素均未升高。相反，6月龄时给一头对照小母牛注射TRH后，其PRL和TSH的血浆浓度升高。这些数据表明，在本研究使用的TRH剂量下，每天两次持续治疗会使激素对TRH刺激的反应性降低。体重增加情况检查表明，TRH长期治疗与6月龄前生长速率增加有关（平均日增重增加10.6%，P<0.10），这在TRH组生长曲线更陡的斜率中表现出来（P<0.05）。TRH处理的小母牛采食量略高，尽管两组间饲料效率（千克饲料/千克增重）无差异。对照小母牛中，PRL的血浆浓度随年龄增加而升高（P<0.01，r=+0.938），而血浆TSH和GH与年龄无显著相关性。这一观察结果确立了PRL分泌与奶牛小母牛青春期临近之间的正相关关系。还注意到，TRH治疗使PRL分泌升高与首次观察到发情的年龄显著提前有关（9.4对 - 10.5月龄），这表明PRL分泌与奶牛小母牛青春期之间可能存在功能关系。
