Endocrinological Causes of Erectile Dysfunction

Testosterone secreted from the Leydig cells of the testes under the influence of luteinizing hormone (LH) is necessary for normal male sexuality and sexual function (Table 4). Medications such as luteinizing hormone-releasing hormone (LHRH) agonists or stilbestrol, which lower circulating testosterone, result in loss of libido and in erectile dysfunction.

Patients who are hypogonadal as a result of pituitary or testicular dysfunction frequently suffer from erectile dysfunction, which responds to treatment with exogenous androgens. More contentious is the suggestion that waning testosterone levels in men of middle age and beyond (Figure 32), the socalled 'male menopause', are a frequent cause of erectile dysfunction and, therefore, boosting serum testosterone levels has therapeutic benefits (Table 5).

Vasculogenic Causes of ED
Neurogenic Causes of ED
Endocrinological Causes of ED
Priapism and Postpriapism ED
Psychogenic Causes of ED

However, there is some evidence from experimental animal models that androgens are necessary for the support of intracavernosal smooth muscle function and maintenance of NO synthase levels. Exogenous androgens are certainly capable of enhancing the libido, which is an important component of sexuality.

Dihydrotestosterone (DHT), the potent androgenic metabolite of testosterone produced by the enzyme 5α-reductase, is crucial for the normal development of the male external genitalia, seminal vesicles and prostate, but is not essential for either the libido or erectile function. Compounds such as finasteride, which inhibit the activity of 5α-reductase type II, result in shrinkage of the prostate by 20–30%, but have been reported to cause erectile dysfunction in only around 3–5% of patients.

However, in the 4-year placebo-controlled study of finasteride recently reported by McConnell and colleagues, nearly 14% of patients taking the active drug experienced some form of sexual dysfunction.

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Prolactin, which is released from the pituitary gland, acts as an inhibitory factor in male sexual function.

Hyperprolactinemia, either idiopathic or, less commonly, the result of a tumor such as a pituitary prolactinoma (Figure 33), is associated with erectile dysfunction, as is the more common entity of idiopathic hyperprolactinemia. Correction of the raised prolactin levels using bromocriptine may sometimes restore potency in such patients.