In order to provide a comprehensive account of pituitary-testicular function in man, 466 subjects, ranging in age from 2 to 101 years, were studied to examine blood levels of the pituitary gonadotrophins (LH and FSH), the sex steroids testosterone and oestradiol, the binding capacity of the sex hormone binding globulin (SHBG), the free testosterone and oestradiol fractions, and the transfer constant for the peripheral conversion of testosterone to oestradiol. The results were compared with clinical indices of testicular size, sexual function and secondary sex hair distribution. Serum LH and FSH were low before puberty, increased in pubertal adolescents to levels somewhat above those of adults and subsequently increased progressively over the age of 40 years. Testosterone levels fell slowly after the age of 40, while there was a slight rise in plasma oestradiol with increasing age. FSH and testosterone showed small seasonal variations in young adult men, the lowest values being seen in winter. SHBG binding capacity was high in two prepubertal boys, fell in adult men, but increased in old age. Free testosterone and oestradiol levels fell in old age. The metabolic clearance rates (MCR) of testosterone and oestradiol also fell in old age, while the conversion of testosterone to oestradiol was increased. Many correlations were observed between various hormonal and clincial measurements. The evidence is consistent with a primary decrease in testicular function over the age of 40 years.
Hypothalamic-pituitary function was studied in 31 patients before and after cranial irradiation for nasopharyngeal carcinoma. The estimated radiotherapy (RT) doses to the hypothalamus and pituitary were 3979 +/- 78 (+/- SD) and 6167 +/- 122 centiGrays, respectively. All patients had normal pituitary function before RT. One year after RT, there was a significant decrease in the integrated serum GH response to insulin-induced hypoglycemia. In the male patients, basal serum FSH significantly increased, while basal serum LH and testosterone did not change. Moreover, in response to LHRH, the integrated FSH response was increased while that of LH was decreased. Such discordant changes in FSH and LH may be explained by a defect in LHRH pulsatile release involving predominantly a decrease in pulse frequency. The peak serum TSH response to TRH became delayed in 28 patients, suggesting a defect in TRH release. Twenty-one patients were reassessed 2 yr after RT. Their mean basal serum T4 and plasma cortisol levels had significantly decreased. Hyperprolactinemia associated with oligomenorrhoea was found in 3 women. Further impairment in the secretion of GH, FSH, LH, TSH, and ACTH had occurred, and 4 patients had hypopituitarism. Thus, progressive impairment in hypothalamic-pituitary function occurs after cranial irradiation and can be demonstrated as early as 1 yr after RT.
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