Regulation of pituitary growth hormone-releasing factor (GRF) receptor gene expression by GRF

We examined how growth hormone-releasing factor (GRF) regulated pituitary GRF receptor gene expression in the conscious rat. GRF receptor mRNA levels were significantly increased by immunoneutralization of endogenous GRF with its specific antiserum. This effect was dose dependent and the maximum level was 3.8-fold higher than that in control rats. A similar rise in GRF receptor gene expression was obtained by the depletion of noradrenaline, a neurotransmitter thought to stimulate GRF release, and was reversed by 87% by the repeated administration of synthetic GRF. These results indicate that pituitary GRF receptor gene expression was up- or down-regulated in vivo in the absence or presence of GRF, respectively.