Clin Endocrinol (Oxf). 1976 Jul;5(4):349-72.
Changes in the pituitary-testicular system with age.
Baker HW, Burger HG, de Kretser DM, Hudson B, O'Connor S, Wang C, Mirovics A, Court J, Dunlop M, Rennie GC.
Abstract
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.
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