In vitro pituitary hormone releasing activity of 40 residue human pancreatic tumor growth hormone releasing factor.
The hypophysiotropic activities of a synthetic human pancreatic growth hormone releasing factor (hpGRF) with 40 residues was examined in vitro using rat pituitary halves. At concentrations from 10(-10) M to 10(-7) M the peptide stimulated GH release in a dose-dependent manner with the ED50 being 1.2 x 10(-9) M. The concentration of 10(-10) M hpGRF is comparable to the basal hypophyseal portal blood levels of other known hypothalamic hypophysiotropic hormones. However, GH release was enhanced three-fold by concentration as low as 10(-12) M, though no dose-response relationship was observed up to 10(-10) M. Thus, this peptide not only stimulates the release of GH in a dose-dependent manner, but at lower concentrations also maintains elevated GH levels. The release of ACTH, beta-endorphin, LH, and FSH was not affected by hpGRF at any of the concentrations tested. At hpGRF concentrations less than 10(-7) M, the release of TSH and PRL were unaffected. However, at 10(-6) M, TSH release was enhanced about 2.5 fold and prolactin release was elevated slightly.