Androgens in Health and Disease.pdf - E Library

Chapter 14/Androgens and Sexual Function 265
and 7 PM) were used. Questions covered the stage of pubertal developmental, though it
is not clear whether spermarche was asked about. The Free-T Index (total T/SHBG) was
found to be a strong predictor of “sexual motivation” and behavior, with stage of pubertal
development not adding to the regression equation. They concluded that “free testosterone
appears to affect sexual motivation directly... and not through the social interpretation
of accompanying pubertal development.” In a later, longitudinal study (43) over 3 yr,
with six monthly questionnaires and hormonal assessments, they were unable to replicate
the earlier cross-sectional findings: The stage of pubertal development was much
more significant in predicting sexual interest and behavior than free T and, furthermore,
no relationship between increasing levels of free T and measures of sexual interest and
activity over the 3-yr period was found. They were unable to explain the differences
between their two studies, but they concluded that hormones are not directly changing
behavior, but that pubertal development is acting as a social signal, both to the boy
himself and potential partners, that he is ready to engage in sexual activity. They did,
however, find that both the level of testosterone and the stage of pubertal development
at the initial assessment were predictors of coital status and sexual interest at later
assessments. They focused on the initial free-T level and suggested that it was “a marker
for an as-yet-unidentified motivational process.”
These were difficult studies to carry out and not easily replicated and we should learn
as much as we can from them. The authors’ interpretations can be questioned on a
number of levels. First, the predictive effect of both free-T and pubertal stage at time 1
is further evidence of the relationship between earlier age at puberty and higher levels
of sexual interest and activity later, first reported by Kinsey et al. (44). This is consistent
with the idea that, in some way, boys with earlier puberty onset may be constitutionally
more interested in sex (and possibly more responsive to T). Second, we should not
assume, as these authors initially did, that the relatively simple relationship between high
and low T levels and sexual interest demonstrated in replacement studies of hypogonadal
men will also be evident in the rising levels of T around puberty. As discussed earlier,
initial hormone replacement in men with delayed puberty shows a more complex and less
predictable hormone–behavior relationship than is found with hypogonadal men who
have gone through normal puberty and adolescent development prior to their hypogonadism
(i.e., hypergonadotrophic hypogonadism). There is a fair amount of socially
influenced learning relevant to sexual behavior at whatever age one goes through this
pubertal process that impacts on the hormone–behavior effects. Third, it is quite possible
that the central mechanisms involving T go through developmental stages as receptor
regulation responds to rising hormone levels. It is also distinctly possible that rising T
levels activate inhibitory mechanisms relevant to sexual response (e.g., the postejaculatory
refractory period). Fourth, possibly the best direct behavioral marker of T
effects, masturbation frequency, was not addressed in these studies; they found low
reporting of masturbation. Halpern et al. (45) have recently followed up some of these
males interviewed initially as young teenagers and asked them as young adults when
they started masturbating. They found that masturbation during adolescence was more
likely to be reported during this adult retrospective recall than during adolescence, by
around 30%. Although we cannot be certain on this point, this is more likely to reflect
underreporting during adolescence than overreporting during early adulthood.
A recent study at the Kinsey Institute has reported such retrospective data from two
groups of men, one a group of undergraduates surveyed in 1998–1999, and the other, a