Circadian variation in testosterone, sex hormone-binding globulin, and calculated non-sex hormone-binding globulin bound testosterone in healthy young and elderly men.
The circadian pattern in levels of serum total testosterone (T) in men becomes blunted with normal aging. However, because T not bound to sex hormone-binding globulin (non-SHBG-T) is felt to be a better representative of biologically available T than is total T, the possibility of a 24-h variation in non-SHBG-T in young men and the possibility that aging is associated with a blunting of that rhythm were investigated. Hourly blood samples were drawn on 10 normal young men (mean age 27.3 years) and 10 normal elderly men (mean age 70.7 years) over a 24-h period and the serum was assayed for total T, sex hormone-binding globulin (SHBG), and total protein; non-SHBG-T was calculated. SHBG was determined by radioimmunoassay as well as by a steroid-binding assay. Young men had a significantly higher (p less than 0.05) mean 24-h level of non-SHBG-T (1.91 +/- 0.62 nm/l) than did the elderly men (0.86 +/- 0.01 nM/l). Also, each young man showed a significant circadian rhythm in non-SHBG-T, with a group mean daily variation of 1.42 +/- 0.38 nM/l. In contrast, only 60% of the elderly men demonstrated a significant circadian rhythm in non-SHBG-T, and the group mean rhythm was blunted (maximum excursion 0.38 +/- 0.07 nM/l) compared with that of the young men. SHBG and total protein levels demonstrated similar 24-h variations in the two age groups. It was concluded that non-SHBG-T serum levels, similar to serum total T levels, demonstrate a circadian pattern in young men and this circadian rhythmicity becomes blunted with normal aging.
Plymate
S R
SR
Department of Clinical Investigation, Madigan Army Medical Center, Tacoma, WA 98431-5454.
Tenover
J S
JS
Bremner
W J
WJ
D000328:Adult; D000368:Aged; D000375:Aging / Q000097:blood*; D001798:Blood Proteins / Q000032:analysis; D002940:Circadian Rhythm / Q000502:physiology*; D006801:Humans; D008297:Male; D012738:Sex Hormone-Binding Globulin / Q000032:analysis* / Q000378:metabolism; D013739:Testosterone / Q000097:blood* / Q000378:metabolism
D001798:Blood Proteins; D012738:Sex Hormone-Binding Globulin; D013739:Testosterone