Abstract
ABSTRACT: The growth hormone-releasing hexapeptide (GHRP-6) specifically stimulates growth hormone (GH) secretion in several animal species and humans. The mechanism of action of GHRP-6 is largely unknown, although experimental evidence indicates that it may modulate growth hormone-releasing hormone (GHRH) and somatostatin actions at the pituitary or hypothalamic level. To gain more insight into the mechanism(s) of action of GHRP-6, we studied the infant rat, an animal model highly responsive to GH-releasing stimuli. In 14-d-old rats GHRP-6 (32–600 μg/kg, s. c.) induced a marked and dose-dependent rise in plasma GH concentrations, maximal stimulation occurring with the dose of 300 μg/kg. Neither GHRH nor somatostatin antiserum prevented or modified the GH release elicited by GHRP-6. In pups passively immunized with GHRH antibodies, a 5-d treatment with GHRP-6 (80 μg/kg, s. c, twice daily) completely counteracted the inhibitory effect of GHRH deprivation on GH mRNA expression. In vitro GHRP-6 (10-7 and 10-6 M) induced a small and transient stimulation of GH release from cultured pituitary cells. These results indicate the following: 1) GHRP-6 is a potent stimulator of GH release in rat pups; 2) it stimulates GH gene expression in the GHRH-deprived pup; 3) during the neonatal period its action is not mediated by GHRH or somatostatin; and 4) its actions are not directed at the somatotrophs.
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Locatelli, V., Grilli, R., Torsello, A. et al. Growth Hormone-Releasing Hexapeptide Is a Potent Stimulator of Growth Hormone Gene Expression and Release in the Growth Hormone—Releasing Hormone—Deprived Infant Rat. Pediatr Res 36, 169–174 (1994). https://doi.org/10.1203/00006450-199408000-00006
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DOI: https://doi.org/10.1203/00006450-199408000-00006