Somatostatin withdrawal alone is an ineffective generator of pulsatile growth hormone release in man.
To assess the relative roles of growth hormone-releasing hormone (GHRH) pulse and somatostatin withdrawal as potential generators of pulsatile growth hormone (GH) release in humans, we studied GH responses to iv bolus GHRH (1 microgram/kg) and to termination of a 4 h iv somatostatin infusion (7.2 micrograms.kg-1.h-1) in five normal young men, and in five men with previously diagnosed isolated GH deficiency. The patients were diagnosed 8-15 years previously on the basis of typical auxological and hormonal criteria, were treated with exogenous GH and were off GH therapy for 1.5-8.9 years prior to this study. Growth hormone rises to a bolus GHRH were similar between the controls and the patients (maximum GH 27.3 +/- 15.3 vs 8.0 +/- 4.0 micrograms/l). The controls exhibited only a small GH rise to somatostatin withdrawal (maximum GH 2.9 +/- 1.2 micrograms/l), while the patients did not (maximum GH 0.7 +/- 0.1 micrograms/l; p < 0.05). We conclude that somatostatin withdrawal by itself is an ineffective promoter of GH pulsatility. Periodic quiescence of somatostatinergic neurons must be associated with a concomitant GHRH pulse in order to result in a robust GH pulse.
Ho
P J
PJ
Department of Medicine, University of Michigan Medical Center, Ann Arbor 48109-0354.
Kletter
G B
GB
Hopwood
N J
NJ
DeMott Friberg
R
R
Barkan
A L
AL
D000328:Adult; D016000:Cluster Analysis; D013006:Growth Hormone / Q000172:deficiency / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology; D006801:Humans; D007262:Infusions, Intravenous; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis; D008297:Male; D010902:Pituitary Gland / Q000378:metabolism*; D011863:Radioimmunoassay; D013004:Somatostatin / Q000008:administration & dosage / Q000097:blood / Q000502:physiology*; D013997:Time Factors
D013004:Somatostatin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone