COMPARISON OF EXERCISE TESTING AND 24-HOUR GROWTH HORMONE SECRETION IN 42 CHILDREN WITH GROWTH RETARDATION

Abstract

At the present time, investigations of physiological growth hormone (GH) secretion are preferred to pharmacological tests. We compared two of the former methods, study of 24-hour GH secretion and exercise testing, in order to clarify their respective usefulness. We studied 42 children (30 boys and 12 girls) with growth retardation (mean = - 3.07 ± 0.9 SD) whose mean age was 12 yr 4mo ± 4 yr 2mo. Thirty-three were at pubertal stage P1 and nine P2. Exercise testing was carried out. using an engametric bicycle and we sought, to obtain maximum effort (maximum VO2, respiratory quotient, heart rate). Sampling was done during the 20 min after the test. Study of 24-hour GH secretion was carried out with sampling every 20 min and the integrated concentration ((C), number of peaks and maximini peak were calculated. Two groups were analysed :

- Group 1 (n - 31) children who had reached maximum effort. Among these children : 24 had normal GH secretion (IG>3 ng/ml and maximum peak > 10 ng/ml), 10 had a normal response to exercise testing (peak > 10 ng/ml) and 9 response < 10 ng/ml; 6 had low 24-hour GH secretion and all these G had a secretory peak < 10 ng/ml in response to exercise.

- Group II (n = 11) children who had reached submaximum effort. None of those children had a GH secretory peak > 10 ng/ml in response to exercise, whereas 24-hour GH secretion was normal in 8/11.

In conclusion, these results show that exercise testing cannot be considered a reliable method of investigation of GH secretion. If effort is submaximum, the percentage of false negatives is 100 % and when effort is maximum there are 36 % false negatives.

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