Synthetic Somatostatin Analog (Octreotide) Suppresses Daytime Growth Hormone Secretion Equivalently in Young and Older Men: Preserved Pituitary Responsiveness to Somatostatin's Inhibition in Aging

Publisher： John Wiley & Sons Inc

E-ISSN： 1532-5415|47|12|1422-1424

ISSN： 0002-8614

Source： JOURNAL OF AMERICAN GERIATRICS SOCIETY, Vol.47, Iss.12, 1999-12, pp. : 1422-1424

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Abstract

OBJECTIVE: To gain greater insight into the mechanisms controlling the low daytime rate of growth hormone (GH) secretion in older men.DESIGN: We conducted a randomized, controlled study of GH secretion during inhibition by octreotide, a somatostatin analog.PARTICIPANTS: Nine young (35–44 years) and ten older (62–79 years) healthy men participated.INTERVENTION: Octreotide versus nothing, while subjects were on a standardized diet.MEASUREMENTS: All subjects were assessed on two separate occasions: baseline and at time of the intervention of octreotide (100 μg subcutaneously); the order of the intervention was randomly assigned. Octreotide was administered at 8:00 a.m. Venous sampling was performed every 10 minutes for 8 hours (8:30 a.m. to 4:30 p.m.). To estimate the joint parameters of pulsatile and basal (between secretory pulses) GH secretion, we used an ultrasensitive chemiluminescence‐based GH assay and multiparameter deconvolution analysis.RESULTS: Compared with baseline, octreotide markedly reduced mean (8‐hour) serum GH concentrations in both young (0.585 ± 0.255 μg/L vs 0.070 ± 0.029 μg/L; P = .008) and older (0.397 ± 0.107 μg/L vs 0.087 ± 0.027 μg/L; P = 0.005) men. In younger men, octreotide decreased the serum GH concentration primarily by suppressing the mass of GH released per secretory pulse (2.4 ± 0.9 μg/L vs 1.0 ± .7 μg/L; P = .015) and the interpulse (basal) rate of GH release (0.0014 ± 0.0003 μg/L/min vs 0.0006 ± 0.0002 μg/L/min; P = .051). In older men, octreotide also restrained the mass of GH per secretory pulse (1.5 ± 0.4 μg/L vs 0.4 ± 0.1 μg/L; P = .028) and lowered basal GH release (0.0014 ± 0.0003 μg/L/min vs 0.0004 ± 0.0001 μg/L/min; P = .007). There were no significant differences when the older men were compared with the young controls.CONCLUSIONS: Our data suggest that the daytime relative GH deficiency seen in older men is not a result of excessive pituitary susceptibility to the inhibitory capabilities of somatostatin, but more likely reflects impoverished endogenous GHRH drive and/or heightened release of brain somatostatin. J Am Geriatr Soc 47:1422–1424, 1999.