Irradiation of the head. Immediate effect on growth hormone secretion in children.

Plasma growth hormone (GH) was determined in samples obtained hourly from 1000 h to 0700 h before, and after a 3 week course of "prophylactic" cranial irradiation, in ten leukemic children who had no clinical or laboratory evidence of central nervous system involvement. The mean per hour value of GH prior to irradiation (4.1 +/- 2.4 ng/ml) was similar to that of 7 endocrinologically normal children (4.09 +/- 2.4 ng/ml), a finding strongly suggesting normal pituitary function prior to irradiation. Following irradiation GH levels at each hour were, in general, lower than before. The difference is statistically significant at 0100 h. The peak GH responses were lower following than preceeding irradiation (p less than 0.02). The findings suggest an immediate suppressive effect of irradiadiation on the apparently normal hypothalamic pituitary axis in children.