Effects of Human Pancreatic Tumor Growth Hormone-Releasing Hormone (hpGRHl-44-NH2) on Immunoreactive and Bioactive Plasma Growth Hormone in Normal Young Men*

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Abstract
Synthetic human pancreatic tumor GH-releasing hormone (hpGRH l-44-NH2) was given by iv bolus injection to 10 normal men at doses of 75, 150, 300, and 600 μg. At all doses the plasma GH responses were similar in an individual subject. Among subjects, however, the responses were significantly different, with peak GH concentrations ranging between 9.0 μg/liter and 54.9 μg/liter. The GH released in response to GRH was bioactive in the Nb2 lymphoma cell multiplication assay. The circulating GH 30 and 60 min after GRH was detected in 3 molecular forms corresponding to little, big, and big-big GH. These forms averaged 50%, 30%, and 20% of the total immunoreactive GH, respectively. The mean rise of plasma somatomedin-C, from 1.86 U/ml to 2.21 U/ml 24 h after GRH, was not statistically significant. A small but statistically significant GRH dose-dependent rise in plasma PRL (mean PRL concentrations 10 min after 600 fig GRH, 11.13 μg/liter occurred consistently after GRH injection. The evidence that the GH released by GRH is bioactive supports the potential use of GRH for therapeutic applications.