Department of Clinical Chemistry, Royal
Liverpool University Hospital, Liverpool, UK. mjdiver@liv.ac.uk
Abstract
BACKGROUND:
Conflicting views are
reported on the association between advancing age and gradually diminishing
concentrations of serum total testosterone in men. The putative المفترضة loss of diurnal rhythm in serum total
testosterone in older men is reported to be in part due to low concentrations
in the morning when compared to concentrations found in young men. We have
measured total, free and bioavailable testosterone along with SHBG in samples
taken every 30 min throughout a 24-h period in 10 young and eight middle-aged
men.
RESULTS:
Both young and
middle-aged men displayed a significant diurnal rhythm in all variables, with a
minimum fall of 43% in total testosterone from peak to nadir in all subjects.
Subjecting the data to a time series analysis by least squares estimation
revealed no significant difference in mesor (P = 0.306), amplitude (P = 0.061)
or acrophase (P = 0.972) for total testosterone between the two groups.
Comparing bioavailable testosterone in the two groups revealed no significant
difference in mesor (P = 0.175) or acrophase (P = 0.978) but a significant
difference (P = 0.031) in amplitude. Both groups display a significant circadian
rhythm (middle-aged group P < 0.001; young group P = 0.014). Free
testosterone revealed a highly significant rhythm in both the young group (P
< 0.001) and the middle-aged group (P = 0.002), with no significant
difference between the groups in mesor (P = 0.094) or acrophase (P = 0.698).
Although analysis of the SHBG data revealed a significant rhythm in the young
group (P = 0.003) and the older group (P < 0.001), the acrophase occurred in
the mid afternoon in both groups (15.12 h in the young and 15.40 h in the
middle-aged). The older men had a significantly greater amplitude (P = 0.044)
but again no significant difference was seen in mesor (P = 0.083) or acrophase
(P = 0.477) between the two groups. Acrophases for total, bioavailable and free
testosterone occurred between 07.00 h and 07.30 h; for SHBG the acrophase
occurred at 15.12 h in the young group and 15.40 h in the middle-aged group.
CONCLUSIONS:
The study suggests that
the diurnal rhythm in these indices of androgen status is maintained in fit,
healthy men into the 7th decade of life.
