The GHRH/GHRP-6 test for the diagnosis of GH deficiency in elderly or severely obese men.
OBJECTIVE
Ageing and obesity result in decreased activity of the GH/IGF-I axis and concomitant impaired GH responses to secretory stimuli. We therefore determined the validity of the GH cut-off value of 15.0 microg/l in the GH-releasing hormone (GHRH)/GH releasing peptide-6 (GHRP-6) test for the diagnosis of GH deficiency in elderly or severely obese men.


METHODS
We performed a combined GHRH/GHRP-6 test in ten elderly men (mean age 74 years; mean body mass index (BMI) 24.6 kg/m(2)), nine obese men (mean age 47 years; mean BMI 40.6 kg/m(2)) and seven healthy male controls (mean age 51 years, mean BMI 24.3 kg/m(2)). After assessment of fasting plasma GH, IGF-I and IGF-binding protein-3 (IGFBP-3), GHRH (100 microg) and GHRP-6 (93 microg) were given intravenously as a bolus injection. Repeated GH measurements were performed for two hours.


RESULTS
Both peak GH levels and areas under the curve (AUC) were significantly lower in the obese than in the controls (peak 13.2 vs 53.4 microg/l, P = 0.001; AUC 707 vs 3250 microg/l x 120 min; P = 0.001). Mean GH response in the elderly was lower than in the controls (peak 35.0 microg/l; AUC 2274 microg/l x 120 min), but this was not statistically significant. In contrast, GH peak levels in seven obese men remained below the cut-off level of 15.0 microg/l associated with severe GH deficiency. All others had GH peak levels exceeding this threshold. IGFBP-3 levels were significantly lower in the elderly than in the controls (1.35 vs 2.05 mg/l, P = 0.001). Baseline GH or IGF-I did not differ significantly between groups.


CONCLUSIONS
GH responses following GHRH/GHRP-6 administration were significantly reduced in severely obese men, but were not significantly reduced in elderly men, despite a negative trend. Our data indicate that the cut-off GH level of 15.0 microg/l after GHRH + GHRP-6 administration for the diagnosis of severe GH deficiency cannot be used in severely obese men.
Haijma
Sander V
SV
Department of Clinical Endocrinology, University Medical Centre, Utrecht, The Netherlands.
van Dam
P Sytze
PS
de Vries
Wouter R
WR
Maitimu-Smeele
Inge
I
Dieguez
Carlos
C
Casanueva
Felipe F
FF
Koppeschaar
Hans P F
HP
D000368:Aged; D000375:Aging; D015992:Body Mass Index; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage; D019382:Human Growth Hormone / Q000097:blood* / Q000172:deficiency*; D006801:Humans; D007275:Injections, Intravenous; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood / Q000150:complications*; D009842:Oligopeptides / Q000008:administration & dosage
D018972:Insulin-Like Growth Factor Binding Protein 3; D009842:Oligopeptides; D019382:Human Growth Hormone; C041048:growth hormone releasing hexapeptide; D007334:Insulin-Like Growth Factor I; D013007:Growth Hormone-Releasing Hormone