There are 4 main components of male sexual function:
Sexual dysfunction is a problem with one of these components that interferes with interest in or ability to engage in sexual intercourse. Many drugs and numerous physical and psychologic disorders affect sexual function.
Libido is the conscious component of sexual function. Decreased libido manifests as a lack of sexual interest or a decrease in the frequency and intensity of sexual thoughts, either spontaneous or in response to erotic stimuli. Libido is sensitive to testosterone levels as well as to general nutrition, health, and drugs.
Drugs that potentially decrease libido include weak androgen receptor antagonists (eg, spironolactone, cimetidine), luteinizing hormone-releasing hormone agonists (eg, leuprolide, goserelin, buserelin) and antagonists (eg, degarelix) used to treat prostate cancer, antiandrogens used to treat prostate cancer (eg, flutamide, bicalutamide), 5-alpha-reductase inhibitors (eg, finasteride, dutasteride) used to treat benign prostatic hyperplasia, some antihypertensives, and virtually all drugs that are active in the central nervous system (eg, selective serotonin reuptake inhibitors [SSRIs], tricyclic antidepressants, antipsychotics). Loss of libido due to SSRIs or tricyclic antidepressants sometimes is reversible with the addition of bupropion or trazodone.
Erection is a neurovascular response to certain psychologic and/or tactile stimuli. Higher cortical input and a sacral parasympathetic reflex arc mediate the erectile response. Neural output travels through the cavernous nerves, which traverse the posterolateral aspect of the prostate. Terminating in the penile vasculature, these nonadrenergic, noncholinergic nerves liberate nitric oxide, a gas. Nitric oxide diffuses into penile arterial smooth muscle cells, causing increased production of cyclic guanosine monophosphate (cGMP), which relaxes the arteries and allows more blood to flow through them and into the corpora cavernosa. As the corpora fill with blood, intracavernous pressure increases, which compresses surrounding venules, causing veno-occlusion and decreased venous outflow. The increased inflow of blood and decreased outflow further increase intracavernous pressure, contributing to erection. Many factors affect the ability to have an erection (see Erectile Dysfunction).
Ejaculation is controlled by the sympathetic nervous system. Neural stimulation of the alpha-adrenergic receptors in the male adnexa (eg, penis, testes, perineum, prostate, seminal vesicles) causes contractions of the epididymis, vas deferens, seminal vesicles, and prostate that transport semen to the posterior urethra. Then, rhythmic contractions of the pelvic floor muscles result in pulsatile ejaculation of the accumulated seminal fluid. At the same time, the neck of the bladder closes, preventing retrograde ejaculation of semen into the bladder. Selective serotonin reuptake inhibitors and alpha blockers may delay or inhibit ejaculation by receptor inhibition at these sites.
Orgasm is the pleasurable sensation that occurs in the brain generally simultaneously with ejaculation. Anorgasmia may be a physical phenomenon due to decreased penile sensation (eg, from neuropathy) or a neuropsychologic phenomenon due to psychiatric disorders or psychoactive drugs.
Ejaculatory dysfunction is reduced or absent semen volume. It may result from retrograde ejaculation, which may occur in men with diabetes or as a complication of bladder neck surgery or transurethral resection of the prostate. It also may result from sympathetic interruption, either due to surgery (eg, retroperitoneal lymph node dissection) or to drugs (eg, guanethidine, phentolamine, phenoxybenzamine, thioridazine). Radical prostatectomy (removal of the prostate gland plus the seminal vesicles and regional lymph nodes) eliminates any ejaculation because removing the seminal vesicles and prostate eliminates semen production.
Premature ejaculation is defined as ejaculation occurring sooner than desired by the man or his partner and causing distress to the couple. It is usually caused by sexual inexperience, anxiety, and other psychologic factors instead of disease. It can be treated successfully with topical anesthetics, sex therapy, tricyclic antidepressants, and selective serotonin reuptake inhibitors.