Dubreuil P, Pelletier G, Petitclerc D, Lapierre H, Couture Y, Brazeau P, Gaudreau P, Morisset J
Department of Biology, University of Sherbrooke, QC, Canada.
Domest Anim Endocrinol. 1987 Oct;4(4):299-307. doi: 10.1016/0739-7240(87)90026-9.
The aim of this study was to determine the effect of age and sex on basal secretory patterns of growth hormone (GH) and growth hormone-releasing factor (GRF) induced GH release. Eighteen pigs (9 castrated males and 9 females) were stimulated with pGRF(1-29)NH2 at 7,11,15,19 and 23 weeks of age. Blood samples were taken from each animal via jugular vein cannulae every 20 min, from 6 hr before to 5 hr after iv GRF administration at a dose of 4 micrograms/kg. GH baseline levels, amplitude of the GH peaks, area under the GH peaks and the overall mean of GH serum levels decreased (P less than .001) with age in both sexes. Age also had a marked effect on GRF-induced GH release: the amplitude of GH peaks and area under the GH peaks decreased (P less than .001) with age. The GH response to pGRF(1-29)NH2 varied considerably, depending on the timing of the episodic endogenous secretion of GH. An immediate response (less than 30 min) was observed when GRF was injected at the end of a trough period or at the beginning of a peak, but there was no immediate response when GRF was injected at the end of a peak or at the beginning of a trough period. Our results show that both endogenous GH secretion and pGRF(1-29)NH2-induced GH release declines with age, suggesting a decreased sensitivity of the somatotroph cells to GRF with age; and that the high variability of the GH response to pGRF(1-29)NH2 stimulation depends greatly on the timing of the episodic endogenous GH release, thus implying a possible episodic endogenous somatostatin secretion by the hypothalamus.
本研究的目的是确定年龄和性别对生长激素（GH）基础分泌模式以及生长激素释放因子（GRF）诱导的GH释放的影响。18头猪（9头去势雄性和9头雌性）在7、11、15、19和23周龄时用pGRF(1 - 29)NH2进行刺激。通过颈静脉插管每20分钟从每只动物采集一次血样，从静脉注射剂量为4微克/千克的GRF前6小时至注射后5小时。两性的GH基线水平、GH峰值幅度、GH峰值下面积以及GH血清水平的总体平均值均随年龄下降（P < .001）。年龄对GRF诱导的GH释放也有显著影响：GH峰值幅度和GH峰值下面积随年龄下降（P < .001）。GH对pGRF(1 - 29)NH2的反应差异很大，这取决于GH间歇性内源性分泌的时间。当在谷值期结束时或峰值开始时注射GRF时观察到即时反应（< 30分钟），但当在峰值结束时或谷值期开始时注射GRF时则没有即时反应。我们的结果表明，内源性GH分泌和pGRF(1 - 29)NH2诱导的GH释放均随年龄下降，提示生长激素细胞对GRF的敏感性随年龄降低；并且GH对pGRF(1 - 29)NH2刺激反应的高度变异性很大程度上取决于间歇性内源性GH释放的时间，从而暗示下丘脑可能存在间歇性内源性生长抑素分泌。
