Borromeo V, Berrini A, Möller F, Secchi C
Institute of Veterinary Physiology and Biochemistry, University of Milan, Italy.
J Endocrinol. 1995 Aug;146(2):271-7. doi: 10.1677/joe.0.1460271.
Clonidine is a specific alpha-2-adrenoreceptor agonist that stimulates growth hormone (GH) release in animals and humans. This drug was used to study the GH and prolactin (PRL) secretory response in dairy cows and heifers. An i.v. infusion of 10 micrograms/kg body weight induced GH release to a peak concentration after 30-60 min, while 2 micrograms/kg had no effect on GH secretory patterns. Plasma PRL decreased significantly (P < 0.01) starting 15-60 min after both doses of clonidine, this effect lasting up to 6 h. Clonidine significantly lowered plasma insulin (P < 0.01) and raised plasma glucose (P < 0.01). The changes in plasma GH, PRL, insulin and glucose differed significantly between doses, the 10 micrograms/kg dose being more effective (P < 0.01). The results of our investigation in dairy cattle provide evidence of (i) an increase in GH release after 10 micrograms/kg clonidine; (ii) a concomitant decrease in PRL secretion, hence GH and PRL secretion in cattle appear inversely controlled; (iii) a significant difference between the effects of the 2 and 10 micrograms/kg doses and (iv) no relationship between the changes in plasma GH and PRL after clonidine and plasma hormone levels before treatment.
可乐定是一种特异性α-2-肾上腺素能受体激动剂，可刺激动物和人类生长激素（GH）的释放。该药物用于研究奶牛和小母牛的GH和催乳素（PRL）分泌反应。静脉注射10微克/千克体重的可乐定，30 - 60分钟后GH释放达到峰值浓度，而2微克/千克对GH分泌模式无影响。两种剂量的可乐定给药后15 - 60分钟开始，血浆PRL显著降低（P < 0.01），这种作用持续长达6小时。可乐定显著降低血浆胰岛素（P < 0.01）并升高血浆葡萄糖（P < 0.01）。不同剂量之间血浆GH、PRL、胰岛素和葡萄糖的变化存在显著差异，10微克/千克剂量更有效（P < 0.01）。我们对奶牛的研究结果证明：（i）10微克/千克可乐定后GH释放增加；（ii）PRL分泌同时减少，因此牛的GH和PRL分泌似乎受到反向控制；（iii）2微克/千克和10微克/千克剂量的作用存在显著差异；（iv）可乐定后血浆GH和PRL的变化与治疗前血浆激素水平之间无关联。
