Carlsson L M, Clark R G, Robinson I C
Department of Physiology, University of Göteborg, Sweden.
J Endocrinol. 1990 Jul;126(1):27-35. doi: 10.1677/joe.0.1260027.
Growth hormone inhibits its own secretion in animals and man but the mechanism for this inhibition is unclear: both stimulation of somatostatin release and inhibition of GH-releasing factor (GRF) release have been implicated. We have now studied the GRF responsiveness of conscious male and female rats under conditions of GH feedback induced by constant infusion of exogenous human GH (hGH). Intravenous infusions of hGH (60 micrograms/h) were maintained for 3 to 6 h whilst serial injections of GRF(1-29)NH2 (0.2-1 microgram) were given at 45-min intervals. The GH responses were studied by assaying blood samples withdrawn at frequent intervals using an automatic blood sampling system. We have confirmed that male and female rats differ in their ability to respond to a series of GRF injections; female rats produced consistent GH responses for up to 13 consecutive GRF injections, whereas male rats showed a 3-hourly pattern of intermittent responsiveness. In female rats, multiple injections of GRF continued to elicit uniform GH responses during hGH infusions, whereas hGH infusions in male rats disturbed their intermittent pattern of responsiveness to GRF, and their regular 3-hourly cycle of refractoriness was prolonged. We suggest that this sex difference in GH feedback may be due to GH altering the pattern of endogenous somatostatin release differentially in male and female rats. Such a mechanism of GH autofeedback could be involved in the physiological control of the sexually differentiated pattern of GH secretion in the rat.
生长激素在动物和人类中均会抑制自身分泌，但其抑制机制尚不清楚：生长抑素释放的刺激和生长激素释放因子（GRF）释放的抑制均与之有关。我们现在研究了在持续输注外源性人生长激素（hGH）诱导的生长激素反馈条件下，清醒雄性和雌性大鼠对GRF的反应性。静脉输注hGH（60微克/小时）持续3至6小时，同时每隔45分钟连续注射GRF(1-29)NH2（0.2 - 1微克）。使用自动采血系统通过分析频繁采集的血样来研究生长激素反应。我们已经证实，雄性和雌性大鼠对一系列GRF注射的反应能力不同；雌性大鼠在连续多达13次GRF注射中产生一致的生长激素反应，而雄性大鼠则呈现每3小时一次的间歇性反应模式。在雌性大鼠中，多次注射GRF在hGH输注期间继续引发均匀的生长激素反应，而雄性大鼠中的hGH输注扰乱了它们对GRF的间歇性反应模式，并且它们每3小时一次的常规不应期周期延长。我们认为，生长激素反馈中的这种性别差异可能是由于生长激素在雄性和雌性大鼠中差异地改变了内源性生长抑素的释放模式。这种生长激素自身反馈机制可能参与了大鼠生长激素分泌性别分化模式的生理控制。
