The mechanism of the adolescent growth spurt induced by low dose pulsatile GnRH treatment.

We have used GnRH administered in a pulsatile fashion to treat 26 patients (12M:14F) with delayed puberty. Treatment was for a mean of 1.05 years (range, 0.3-1.6). Mean age at the onset of treatment was 16.4 years in the girls (range, 12.7-28.2) and 15.8 years in the boys (range, 13.8-17.8). At different stages of sexual maturation, overnight serum samples for growth hormone (GH) were taken at 15 min intervals between 2000 h and 0600 h. The girls had a peak growth velocity which occurred between breast stages 2 and stage 3 (B2/3). GH secretion (both sum of the GH peaks and area under the GH pulse) increased at B2 and reached a peak at B3. Growth acceleration in the boys started at the attainment of a 9-10 ml testicular volume and reached a peak at 11-15 ml. The boys demonstrated an initial fall in GH secretion with the onset of treatment until the attainment of 9-10 ml testicular volume; peak GH secretion occurred at the attainment of 11-12 ml testicular volume. There was no change in GH pulse frequency during treatment in either sex. These observations and the maintenance of the normal relationship of the growth spurts to the appearance of secondary sexual characteristics are relevant to the mechanisms and timing of the adolescent growth spurts in normal girls and boys.