Activity of growth hormone-releasing peptide-2 in cultured human pituitary adenoma cells and its interaction with growth hormone-releasing hormone and somatostatin

Experiments on primary cultures of human pituitary adenoma cells producing growth hormone (GH) or GH and prolactin showed that similarly to GH-releasing hormone (GHRH) synthetic hexapeptide GH-releasing peptide-2 (GHRP) directly enhance secretion of GH but not of prolactin by human pituitary cells. The effect of various doses of GHRP and GHRH applied in combination was additive or slightly synergistic in nature. Somatostatin inhibits secretion of GH induced by GHRP, GHRH, or their combination. A dissociation is found between the inhibitory effects of somatostatin on basal and stimulated GH secretion.