Physical activity or food intake prior to testing did not affect the reproducibility of GH secretion elicited by GH releasing hormone plus GH-releasing hexapeptide in normal adult subjects.
OBJECTIVE
Growth hormone deficiency (GHD) in adults is a defined syndrome of which the adverse effects on different areas of body function are reversed under replacement therapy with GH. The diagnosis of GHD is controversial in adults, relying on the GH secretion elicited by the so-called provocative tests of GH reserve. Most of the tests in use, including the widely employed insulin tolerance test, have been shown to be blunted after daily activities, such as mild exercise, heat or food intake, which makes stringent testing conditions mandatory in order to assure reproducibility. The combined administration of GH releasing hormone (GHRH) and GH-releasing hexapeptide (GHRP-6) is a very effective test for the diagnosis of GH deficiency in adults. In the present study, the perturbatory action of mild physical activity and food intake on the reproducibility of this combined test was assessed.


METHODS
Seventeen healthy volunteers of both sexes were tested twice on separate occasions with the sequential administration of GHRH (90 microg i.v.) plus GHRP-6 (90 microg i.v.) as bolus. Eleven subjects underwent the first combined test in the morning under basal conditions and the second test was performed in the afternoon of the same day after a morning of habitual working activity and after a standard lunch. Another group of six subjects underwent similar double testing in the morning and in the afternoon after morning activity followed by lunch; however, both tests were separated by a period of 6 months.


METHODS
GH levels were analysed by time-resolved fluoroimmunoassay, with sampling every 15 minutes.


RESULTS
The reproducibility of the GHRH + GHRP-6 test performed on the same day was high, with the mean GH peak being 65.4 +/- 8.0 microg/l in the basal state and 51.2 +/- 9.6 microg/l after lunch, while the area under the curve (AUC) was 2287 +/- 288 microg/l per 45 minutes in the morning and 1759 +/- 350 after lunch. When a period of 6 months had elapsed between the first and the second test, the reproducibility was well maintained with a mean GH peak of 42.7 +/- 6.2 microg/l in the basal state and 34.3 +/- 3.6 microg/l in the after lunch test, with the AUC 1463 +/- 209 and 1164 +/- 106 microg/l per 45 minutes in the morning and after lunch, respectively. When analysed individually, physical activity, lunch or time elapsed between the two tests did not significantly change the GH peak in the subjects tested.


CONCLUSIONS
The GHRH + GHRP-6 test of GH reserve is a highly reproducible test in adult subjects over time, and is not perturbed by common daily activities, such as mild physical exercise or food intake. Considering that stringent testing conditions are not required and the whole test may be performed in 30 minutes, it may be useful in the clinical setting for the diagnosis of GH deficiency in adults.
Popovic
Vera
V
Institute of Endocrinology, University Clinical Centre, Belgrade, Yugoslavia.
Pekic
Sandra
S
Simic
Mirjana
M
Damjanovic
Svetozar
S
Micic
Dragan
D
Dieguez
Carlos
C
Casanueva
Felipe F
FF
D000328:Adult; D019540:Area Under Curve; D004435:Eating / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D013007:Growth Hormone-Releasing Hormone; D006801:Humans; D008297:Male; D008875:Middle Aged; D009842:Oligopeptides; D015203:Reproducibility of Results
D009842:Oligopeptides; C041048:growth hormone releasing hexapeptide; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone