Certain authors use the nocturnal penile tumescence to separate organic causes of sexual impotence from psychological ones. It has been hypothesized that the presence of nocturnal penile tumescence in a patient with failure to erect during coitus points to psychological origins, while a complete absence of erection to organic origin. But such a relationship has been documented until now only for sexually impotent patients with diabetes mellitus.
In addition to nocturnal penile tumescence, endocrine and neuroendocrine research has been of assistance in identifying possible physiological causes of sexual impotence. It is hypothesized that testosterone plays an important role in regulating the sexual behavior of the male. This hypothesis is supported by the following findings:
- For patients with nocturnal penile in whom an androgen-deficiency has been shown (e.g. castrates, hypogonadism), androgen-substitution therapy is found to be effective.
- After administration of anti-androgens, sex drive is diminished, volume of the ejaculate decreases and spermatogenesis is inhibited. These symptoms are reversible after discontinuation of the drug.
- In males over 60 years of age there is a relationship between lowered sexual activity and a decrease in testicular contents, decrease of fructose in sperm, decrease of plasma testosterone and increase of plasma gonadotropins. To date, it has not been determined whether there is a cause-effect relationship between the lowered plasma testosterone concentration and the diminished sexual activity that occurs with age.
In addition to androgens, there is also a question about the relative importance of estrogens in male sexual behavior. The only experimental results available that would substantiate the hypothesis that an interaction of androgens and estrogens provides for the basis of male sexual behavior patterns are those obtained in animals.
In recent years, endocrine and neuroendocrine studies have also been performed on patients where psychological causes were most suspect. Plasma testosterone in these patients was found to be normal in some and decreased in others. These contradictory results could be partially due to methods of measurement. In another study on patients with nocturnal penile where capacity for erection was decreased or non-existent and where this condition has lasted a minimum of a year, the average values of total plasma testosterone in 30 patients tested lie within normal limits. However, 5 of these 30 patients showed pathologically decreased values.
Plasma-luteinizing hormone (LH) as well as plasma follicle-stimulating hormone (FSH) were not abnormally altered in the above-mentioned patient groups. There are some indications that the functionality of the hypothalamo-pituitary-gonadal axis could be altered in impotent patients.
No differences were discerned in plasma prolactin (PRL) levels. On the other hand, sexual impotence is sometimes found among patients with elevated prolactin levels. Sexual disorders decreased in these patients after lowering plasma prolactin levels with bromocriptine.
In addition to physiological, endocrine and neuroendocrine studies on patients with sexual impotence, a few controlled pharmacotherapeutic studies were also conducted in the last years. Because of multiple methodological problems, only very small groups could be used in pharmacotherapeutic studies. Most literature that deals with the possibility of pharmacotherapy in sexual impotence deals with single case studies or pilot studies without placebo control groups. The use of control groups, however, seems highly indicated with this particular type of patient group. In our own controlled pharmacotherapeutic studies, in about 50% of the cases therapeutic success could be determined after administration of a placebo. Because of such a strong placebo effect, it becomes difficult to prove any significant therapeutic effectiveness of a drug. It is understandable that there is no satisfactory substantiated basis for the assumed effectiveness of the widespread pharmacotherapeutic use of hormone preparations, psychostimulants or aphrodisiacs.
In the following, drugs are described that have been prescribed in instances of sexual impotence or whose effectiveness has been observed or experimentally tested.