Plasma growth hormone secretion during constant growth hormone-releasing factor infusion.

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Abstract
Synthetic human pancreatic growth hormone-releasing factor (hpGRF-44) was infused i.v., at a constant rate of 2.5 .mu.g/min for 180 min in 3 normal boys of short stature. Plasma GH [growth hormone] levels reached a peak at 60-120 min with a mean value (.+-. SEM [standard error of the mean]) of 69.1 .+-. 14.3 ng/ml, and then, declined gradually in spite of continuous hpGRF-44 infusion up to 180 min. Similarly, constant infusion of hpGRF-44 at a rate of 2.5 .mu.g/min in 5 normal but short boys for 90 min, together with an i.v., bolus injection of hpGRF-44 (2 .mu.g/kg) administered at 0 and 90 min, elicited a prompt rise in plasma GH 15-30 minutes after the 1st bolus but no significant elevation of GH was observed after the 2nd bolus. When 2 i.v., bolus injections of hpGRF-44 (2 .mu.g/kg) were given in 4 normal boys with short stature at 0 and 90 min, respectively, significant elevation of plasma GH was found after each bolus. Apparently, under constant infusion of GRF the pituitary experiences a down-regulation after the initial peak of GH response, possibly due to desensitization to GRF.

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