Effects of cranial radiation on hypothalamic-adenohypophyseal function: abnormal growth hormone secretory dynamics.
The function of the hypothalamic-adenohypophyseal unit was tested in 2 groups of rhesus monkeys before and at periodic intervals after the administration of 2400 and 4000 rads cranial radiation. This therapy was given in 10 fractions over a 2-week period. Plasma TSH, basally and after TRH administration, and LH and FSH, before and after gonadotropin-releasing hormone stimulation, were normal up to 1 yr after radiation. Plasma GH at the basal state and after arginine and L-dopa stimulation was also normal. An insulin tolerance test, however, demonstrated a blunted GH response at a dose (0.1 U/kg) that caused brisk stimulation of GH secretion in normal control monkeys. A larger dose of insulin (0.2 U/kg) resulted in ample secretion of GH in these animals, suggesting decreased hypothalamic sensitivity to insulin in treated animals. The measurement of GH every 20 min for 24 h in animals treated with 4000 rads showed a dramatically altered secretory pattern of GH 1 yr after radiation. GH secretory spikes were markedly decreased in both frequency and amplitude, suggesting a reduction in the normal daily production of GH.
D000818:Animals; D001120:Arginine; D006062:Gonadotropins / Q000097:blood; D013006:Growth Hormone / Q000097:blood*; D007030:Hypothalamo-Hypophyseal System / Q000528:radiation effects*; D007328:Insulin; D007980:Levodopa; D008137:Longitudinal Studies; D008253:Macaca mulatta; D008297:Male; D011388:Prolactin / Q000097:blood; D011446:Prospective Studies; D013972:Thyrotropin / Q000097:blood
D006062:Gonadotropins; D007328:Insulin; D007980:Levodopa; D011388:Prolactin; D013972:Thyrotropin; D013006:Growth Hormone; D001120:Arginine