Plasma Growth Hormone Responses to Constant Infusions of Human Pancreatic Growth Hormone Releasing Factor Intermittent Secretion or Response Attenuation

As bstract. Administration ofhuman pancreatic tumor growth hormone (GH) releasing factor (hpGRF [ 1-40]) as a single injection to normal human subjects stim-ulates the secretion ofGH in a dose-responsive manner. In the present studies, hpGRF(1-40) was infused in a graded stepwise manner over a 6-h period in order to determine whether the GH secretory response would be sustained. Normal adult males received four consecutive 90-min infusions of hpGRF(1-40) at doses of 1, 3.3, 10, and 33 ng/kg per min, preceded and followed by a 90-min saline infusion; and the plasma GH responses were compared with those during a separate control infusion. Plasma GH levels were significantly elevated by each hpGRF(1-40) infusion; and dose responsiveness was ev-ident for the lowest three doses. Mean integrated GH secretory rates for the four doses were 1.95, 3.29, 4.29, and 3.65 times those of the respective control study. Plasma GH responses exhibited considerable variability, frequently decreasing during the latter part of each in-fusion; and at the highest dose, they decreased contin-uously beginning shortly after the onset of infusion. Ep-isodic GH secretion occurred in individual subjects during each of the infusion periods. The possible contribution of hypothalamic somato-statin secretion to the diminished GH responsiveness was evaluated by determining plasma thyroid stimulating hormone (TSH) levels during the infusions and the TSH Address correspondence to Dr. Frohman at University of Cincinnati. Received for publication 25 October 1983 and in revised form 2