Key result
Pulsatile GHRH administration at a 1.5-h frequency doubled GH mRNA, elevated pituitary GH stores, and stimulated body weight gain in female rats, whereas continuous infusions were ineffective.
Why the study?
Does pulsatile GHRH administration improve pituitary GH mRNA levels and somatic growth in female rats compared to continuous infusion?
Does pulsatile GHRH administration improve pituitary GH mRNA levels and somatic growth in female rats compared to continuous infusion?
In a rat model, pulsatile but not continuous GHRH administration effectively induces pituitary GH mRNA, GH content, and somatic growth.
Pulsatile GHRH effects in rats warrant clinical caution; leaves open translation to human GH regulation or therapy.
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.
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Borski et al. (2000) studied this question. Pulsatile Growth hormone-releasing hormone (GHRH) vs. Continuous GHRH infusions was evaluated on Pituitary GH mRNA, GH content, and somatic growth. Pulsatile GHRH administration at a 1.5-h frequency doubled GH mRNA, elevated pituitary GH stores, and stimulated body weight gain in female rats, whereas continuous infusions were ineffective.
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