It is commonly accepted that low serum testosterone may result in the combination of low sexual desire and erectile difficulties. In many patients, the correlation between sexual function and serum testosterone values follows this logical pattern. Although this is a practical concept, and one that has been examined experimentally, the reality is not always as simple or clear. 
Hypogonadal men may be capable of sexual erections with Viagra professional online Australia; for exam-ple, only 75% of men who received anti-androgen therapy were unable to develop erec-tions when tested with erotic video challenge. Additionally, hormonal supplementation resulting in normal testosterone values does not always result in restoration of libido and quality of erectile function. The presence of penile erections has been documented in male fetuses by antenatal ultrasound and castrati who have negligible circulating tes-tosterone. Therefore, in some circumstances, there appears to be a disconnect between the biochemical picture and the clinical situation.
Hypogonadism has been shown to reduce the frequency of sexual thoughts and inter-course. Low testosterone levels also decrease the frequency, volume, and quality of ejaculation. The effect of testosterone on different aspects of erectile function has been studied, and the current belief is that nocturnal penile tumescence and spontaneous erections are androgen-dependent. Audiovisual erotic stimulation predominantly causes erections through androgen-insensitive pathways, but some androgen sensitivity is likely. Rapid-eye-movement sleep has been shown to be reduced in hypogonadism, and although androgen reduction adversely affects sleep-related erections, it did not elimi-nate them over a 12-wk trial in healthy young adult men.
There are data for supranormal levels of testosterone from the exogenous administration of testosterone to normal males. The patterns of sexual intercourse, masturbation, and sexual interest were not found to change significantly. The information in this area has previously suggested compart-mentalization, with various functional aspects having different androgen sensitivities; the issue is unresolved but the sensitivities appear to overlap. The prospect that selective androgen modulation may be therapeutically harnessed remains a possibility. Certain types of age-related changes are associated with the length of the AR gene CAG repeat. CAG repeat lengths may play a role in setting different thresholds for the various androgen actions.