Short-term glucocorticoid administration decreases both hypothalamic and pituitary galanin synthesis in the adult male rat

Galanin (GAL) is a peptide that has been implicated in the regulation of the growth axis. It is generally accepted that GAL can increase serum growth hormone (GH) levels, although the underlying mechanism for this increase is unknown. It is well known that long-term glucocorticoid treatment alters in vivo GH secretion, since there is a decrease in serum GH in response to stimuli. It has previously been shown in our laboratory that administration of GAL can overcome the effects of glucocorticoid administration on GH secretion. The aim of the present study was to determine the effects of long-term glucocorticoid administration on the regulation of hypothalamic and pituitary GAL mRNA levels. Adult male rats were treated for 72 hours with the synthetic glucocorticoid dexamethasone ([DEX] 40 μg/kg/d intraperitoneal injections). RNase protection assays were performed on both the hypothalamus and pituitary for the presence of GAL mRNA. As expected, DEX significantly decreased somatic growth, as evidenced by a decrease (50%) in the weight gain of glucocorticoid-treated versus control animals. It was also demonstrated that in both the hypothalamus and pituitary, glucocorticoid treatment reduced the level of GAL mRNA (to 11% and 6.5%, respectively) compared with the control condition. We conclude that the decrease in GAL mRNA may lead to a decrease in GAL secretion, which in turn may be involved in the glucocorticoid-induced inhibition of GH secretion.