Borski R J, Tsai W, Demott-Friberg R, Barkan A L
Department of Zoology, North Carolina State University, Raleigh, North Carolina 27695, USA.
Am J Physiol Endocrinol Metab. 2000 May;278(5):E885-91. doi: 10.1152/ajpendo.2000.278.5.E885.
Growth hormone-releasing hormone (GHRH) is a main inducer of growth hormone (GH) pulses in most species studied to date. There is no information regarding the pattern of GHRH secretion as a regulator of GH gene expression. We investigated the roles of the parameters of exogenous GHRH administration (frequency, amplitude, and total amount) upon induction of pituitary GH mRNA, GH content, and somatic growth in the female rat. Continuous GHRH infusions were ineffective in altering GH mRNA levels, GH stores, or weight gain. Changing GHRH pulse amplitude between 4, 8, and 16 microg/kg at a constant frequency (Q3.0 h) was only moderately effective in augmenting GH mRNA levels, whereas the 8 microg/kg and 16 microg/kg dosages stimulated weight gain by as much as 60%. When given at a 1.5-h frequency, GHRH doubled the amount of GH mRNA, elevated pituitary GH stores, and stimulated body weight gain. In the rat model, pulsatile but not continuous GHRH administration is effective in inducing pituitary GH mRNA and GH content as well as somatic growth. These studies suggest that the greater growth rate, pituitary mRNA levels, and GH stores seen in male compared with female rats are likely mediated, in part, by the endogenous episodic GHRH secretory pattern present in males.
生长激素释放激素（GHRH）是迄今为止所研究的大多数物种中生长激素（GH）脉冲的主要诱导物。关于作为GH基因表达调节因子的GHRH分泌模式尚无相关信息。我们研究了外源性GHRH给药参数（频率、幅度和总量）对雌性大鼠垂体GH mRNA诱导、GH含量和体细胞生长的作用。持续输注GHRH对改变GH mRNA水平、GH储备或体重增加无效。在恒定频率（每3.0小时一次）下，将GHRH脉冲幅度在4、8和16微克/千克之间改变，对增加GH mRNA水平仅有中等效果，而8微克/千克和16微克/千克剂量使体重增加多达60%。当以1.5小时的频率给药时，GHRH使GH mRNA量增加一倍，提高了垂体GH储备，并刺激了体重增加。在大鼠模型中，脉冲式而非持续给予GHRH可有效诱导垂体GH mRNA和GH含量以及体细胞生长。这些研究表明，与雌性大鼠相比，雄性大鼠中更高的生长速率、垂体mRNA水平和GH储备可能部分由雄性中存在的内源性间歇性GHRH分泌模式介导。
