Selective inhibition of sleep related growth hormone release by Phe-4-somatostatin. 
We have compared the effects of somatostatin (SS) and the somatostatin analog Phe-4-SS on nocturnal GH secretion in three normal male volunteers, 20 to 23 years of age.  Subjects were studied in our sleep laboratory on 5 consecutive nights.  Nights 1 and 2 were used for adaptation.  On the third night (control night), all patients exhibited a typical GH peak accompanying slow-wave sleep, with maximum GH levels from 9.2 to 27 ng/ml.  Insulin, glucagon and glucose levels were episodic and sleep-independent.  On night 4, subjects received SS infusion at a rate of 3 micrograms/min, which inhibited GH levels consistently below 2.4 ng/ml.  In two cases a post-infusion rebound of GH levels was observed.  During SS infusion all three subjects showed a significant decrease in insulin levels (p less than 0.0005), followed by an immediate rebound after infusion was stopped.  Glucagon levels fell significantly during infusion (p less than 0.001, p less than 0.025 and p less than 0.00025 respectively).  Glucose was significantly higher than on control night in subject No.  3 (p less than 0.0005) and similar to control night in subjects 1 and 2.  On the fifth night, Phe-4-SS was infused at a rate of 0.75 microgram/min.  GH levels decreased significantly as compared to control night in all three subjects and remained virtually constant throughout the night.  Insulin levels were diminished in subject No.  1 (p less than 0.0005), but were comparable to control values in subjects 2 and 3.  Cessation of analog infusion was followed by a rebound in insulin levels in all three subjects.  Glucagon values were not significantly lowered and the rebound effect was not apparent.  Glucose levels were higher in response to Phe-4-SS than on control night, and fell below infusion values (p less than 0.001) after administration was discontinued.  It was concluded that Phe-4-SS inhibits nocturnal secretion of GH more selectively than SS, but its effect is not more prolonged than that of SS.