Maximal secretory capacity of somatotrope cells in obesity: comparison with GH deficiency.
OBJECTIVE
To evaluate the maximal secretory capacity of somatotrope cells in obesity and to compare it with that in hypopituitaric patients with GH deficiency.


METHODS
Stimulation with GHRH. (1 microgram/kg i.v.), combined with arginine (ARG, 0.5 g/kg i.v.), which strongly potentiates the GH response to the neurohormone, likely inhibiting hypothalamic somatostatin. The reproducibility of the GH response to GHRH + ARG was evaluated in a second session.


METHODS
Forty-five patients with simple obesity (OB 11 male and 34 female, age 40.5 +/- 1.8 y, BMI 38.8 +/- 1.1 kg/m2), 49 patients with hypopituitarism (GHD, 23 male and 26 female, 43.6 +/- 2.4 y, 24.7 +/- 0.7 kg/m2) and 44 normal young volunteers (NS, 25 male and 19 female, 33.8 +/- 1.0 y, 21.6 +/- 0.3 kg/m2) were studied.


METHODS
GH levels were assayed by IRMA method, basally at -60 and 0 min, and than every 15 min up to +120 min. Basal IGF-I levels were assayed by RIA method, after acid-ethanol extraction.


RESULTS
IGF-I levels in OB were lower (P < 0.005) than those in NS but higher (P < 0.005) than those in GHD. Mean peak GH response to GHRH + ARG in OB was clearly lower than that in NS (P < 0.005) and higher (P < 0.005) than that in GHD. Sixty-percent OB and 100% GHD showed peak GH responses lower than the minimum normal limit in NS (16.5 micrograms/l) while 4% OB and only 53% GHD with GH responses lower than 3 micrograms/l, the limit under which GH replacement therapy of severe deficiency is allowed. Good intraindividual reproducibility of the GH response to GHRH + arginine test was present in all groups (OB: r = 0.78, P < 0.0001; GHD: r = 0.57, P < 0.003; NS: r = 0.74, P < 0.0001;.


CONCLUSIONS
The maximal secretory capacity of somatotrope cells is clearly less than normal in the obese but still more than is seen in GHD subjects. However, in about 50% of obese patients, the pituitary GH releasable pool overlaps with that of hypopituitaric patients with GH deficiency. Thus, even when the maximal secretory capacity of somatotrope cells is evaluated by a potent and reproducible provocative tests such as GHRH + arginine, overweight has to be taken in a great account as the cause of severely impaired GH response in patients with suspected GH deficiency.
Maccario
M
M
Department of Internal Medicine, University of Turin, Italy.
Valetto
M R
MR
Savio
P
P
Aimaretti
G
G
Baffoni
C
C
Procopio
M
M
Grottoli
S
S
Oleandri
S E
SE
Arvat
E
E
Ghigo
E
E
D000328:Adult; D001120:Arginine / Q000494:pharmacology; D005260:Female; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D019382:Human Growth Hormone / Q000097:blood / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007018:Hypopituitarism / Q000097:blood* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood* / Q000378:metabolism; D015203:Reproducibility of Results; D013997:Time Factors
D019382:Human Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D001120:Arginine