The effect of high-dose cranial- and craniospinal irradiation and chem
otherapy on the gonadotropin-sex steroid axis was studied during diffe
rent stages of puberty by measuring pulsatile secretion of luteinizing
hormone (LH), follicle-stimulating hormone (FH) and testosterone. The
patients were thirteen boys who had been treated for malignant brain
tumor residing well away from the hypothalamo-pituitary region. The me
dian time to follow-up was 9 (1-16) years. The onset of puberty was ea
rly in the patients, median 10.5 years, compared to the average age fo
r Swedish boys, which is at median 12.4 years. There was, before puber
ty, no significant difference in LH and FSH secretion between patients
and a control group of normal boys. in early, mid- and late stages of
puberty, however, LH and FSH secretion was increased in the patients
overall, whereas testosterone secretion was maintained within the norm
al range in spite of signs of gonadotoxocity with small testicular vol
umes. These results indicate that the vulnerable parts of the gonadotr
opin releasing hormone (GnRH)-gonadotropin (LH, FSH)-gonadal axis are
the regulatory system that determines the timing of pubertal induction
and the gonads. The GnRH-LH, FSH-releasing neurons appear relatively
resistant to cranial irradiation as they are able to respond with supr
anormal LH and FSH levels for long periods of time after treatment. (C
) 1997 Wiley-Liss, Inc.