Plouzek C A, Molina J R, Hard D L, Vale W W, Rivier J, Trenkle A, Anderson L L
Department of Animal Science, Iowa State University, Ames 50011.
Proc Soc Exp Biol Med. 1988 Nov;189(2):158-67. doi: 10.3181/00379727-189-42792.
The effects of growth hormone-releasing factor (GHRF) on growth hormone (GH) secretion were studied in beef calves after hypophysial stalk transection (HST). Peripheral GH concentration during surgery was elevated for 60 min after the initiation of anesthesia to 15 ng/ml, which was greater than plasma levels after HST and during the recovery period (0-30 hr mean, 3 ng/ml; P less than 0.05). Episodic GH secretion normally seen in sham-operated controls (SOC) was abolished after HST. Before HST, calves responded to 80% of the GHRF challenges, whereas after HST calves responded to every challenge of GHRF with an increase in plasma GH. A dose of 0.067 microgram human pancreatic (hp) hpGHRF(1-40)OH/kg body wt 3 days after HST increased plasma GH to 55 ng/ml from a control period mean of 5 ng/ml (P less than 0.04). On Day 8, HST calves received two injections of 0.067 microgram hpGHRF/kg body wt at 3-hr intervals, with feeding 70 min after the first injection. During two preinjection control periods, basal GH averaged less than 4 ng/ml and increased to 17 (P less than 0.02) and 9 (P less than 0.04) ng/ml immediately after the first and second injection of hpGHRF, but the response declined over the 8-day period after surgery. On Days 19 and 20, the HST calves were infused iv with 0.033 and 0.067 microgram somatostatin(SS)-14 (SRIH)/kg body wt, during which a pulse injection of 0.067 microgram hpGHRF/kg body wt was administered. GH increased to 9 and 5 ng/ml during the 0.033- and 0.067-microgram SRIH infusions after GHRF; no somatotropic rebound was observed after the SRIH was discontinued as was seen in the animals while the hypothalamic-hypophysial connections were intact. Five and six months after HST the responses to two analogs of rat hypothalamic GHRF were similar to those in SOC calves. These results indicate that HST calves responded to exogenous GHRF with an abrupt increase in plasma GH, but GH response to GHRF during SRIH infusion was greatly inhibited.
在肉牛犊进行垂体柄横断术（HST）后，研究了生长激素释放因子（GHRF）对生长激素（GH）分泌的影响。麻醉开始后60分钟内，手术期间外周血GH浓度升高至15纳克/毫升，高于HST后及恢复期的血浆水平（0 - 30小时平均值为3纳克/毫升；P < 0.05）。假手术对照组（SOC）中正常出现的GH阵发性分泌在HST后消失。在HST前，犊牛对80%的GHRF刺激有反应，而在HST后，犊牛对每次GHRF刺激均有血浆GH升高的反应。HST后3天，剂量为0.067微克人胰腺（hp）hpGHRF(1 - 40)OH/千克体重可使血浆GH从对照期平均值5纳克/毫升升高至55纳克/毫升（P < 0.04）。在第8天，HST犊牛每隔3小时接受两次0.067微克hpGHRF/千克体重的注射，第一次注射后70分钟喂食。在两个注射前对照期，基础GH平均低于4纳克/毫升，在第一次和第二次注射hpGHRF后立即分别升至17纳克/毫升（P < 0.02）和9纳克/毫升（P < 0.04），但手术后8天内反应逐渐下降。在第19天和第20天，给HST犊牛静脉输注0.033和0.067微克生长抑素（SS）-14（SRIH）/千克体重，在此期间脉冲注射0.067微克hpGHRF/千克体重。在GHRF后，0.033微克和0.067微克SRIH输注期间GH分别升至9纳克/毫升和5纳克/毫升；与下丘脑 - 垂体连接完整的动物不同，停止SRIH输注后未观察到生长激素释放反弹。HST后5个月和6个月，对两种大鼠下丘脑GHRF类似物的反应与SOC犊牛相似。这些结果表明，HST犊牛对外源性GHRF有血浆GH突然升高的反应，但在SRIH输注期间对GHRF的GH反应受到极大抑制。
