Growth hormone regulation by growth hormone-releasing hormone in infant rhesus monkeys

To study the relationship of endogenous GHRH to the changes seen in serum GH concentration in neonatal primates, we administered antiserum to GHRH (GHRH-Ab) or GHRH antagonist, (N-Acetyl-Tyr¹, D-Arg2)GHRH-(1-29)-NH₂, to unanesthetized, fasted rhesus monkeys, 1-31 days of age, via an acutely placed venous catheter. The administration of GHRH-Ab resulted in a significant decrease in serum GH concentration at 1-2 and 7-9 days, but not at 28-31 days of age. The administration of GHRH antagonist resulted in a significant decrease in serum GH concentrations at 1-2 days, but not at 7 or 14 days of age. These results imply that basal serum GH is more dependent on endogenous GHRH at 1-2 days than after 7-28 days of age. This suggests developmental changes in the hypothalamic regulation of GH secretion with advancing age in the neonatal period.