The Effects of Cranial Irradiation on Growth Hormone Secretion

Abstract

Growth hormone (GH) secretion has been studied under physiological conditions and in response to standard pharmacological stimuli in 14 children, who had previously received cranial irradiation between two and fourteen years earlier. All fourteen showed a blunted GH response to insulin hypoglycaemia and, in twelve, the GH response to arginine stimulation was also subnormal. Physiological GH secretion was studied by measuring integrated GH concentrations in 30 min blood samples collected over a 24 hour period by a continuous withdrawal pump. Compared to normal controls (n=5), the irradiated patients showed a significant reduction in the mean integrated GH concentration (2.2: 8.8 mU/l; p< 0.002), the total 24 hour GH output (mean 105.7 mU vs. 391.7 mU; p< 0.002) and the mean GH output during the first six hours of sleep (mean 48.2 mU vs. 226 mU; p< 0.002). There was no significant correlation between the maximum peak GH response to either pharmacological test and the total 24 hour GH output. Conventionally most short children undergo two provocative tests of GH release and if the GH response to one of the two tests is normal, it is usually assumed that GH production is adequate. Adopting these criteria in this study it would have been assumed incorrectly that GH production was normal in two children. Nonetheless all 14 children showed a blunted GH response to an ITT as well as a reduced total 24 hour GH output. Therefore we would suggest that in children suspected of radiation-induced GH deficiency pharmacological tests of GH secretion remain useful, the ITT being the test of choice because of the marked radiation sensitivity of the GH response to hypoglycaemia.