Overview of Male 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.

Conditions particularly likely to decrease libido include hypogonadism Male Hypogonadism Hypogonadism is defined as testosterone deficiency with associated symptoms or signs, deficiency of spermatozoa production, or both. It may result from a disorder of the testes (primary hypogonadism)... read more , chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more , and depression Depressive Disorders Depressive disorders are characterized by sadness severe enough or persistent enough to interfere with function and often by decreased interest or pleasure in activities. Exact cause is unknown... read more ; up to 25% of men with diabetes Diabetes Mellitus (DM) Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more may meet the definition of hypogonadism.

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 Prostate Cancer Prostate cancer is usually adenocarcinoma. Symptoms are typically absent until tumor growth causes hematuria and/or obstruction with pain. Diagnosis is suggested by digital rectal examination... read more (eg, flutamide, bicalutamide), 5-alpha-reductase inhibitors (eg, finasteride, dutasteride) used to treat benign prostatic hyperplasia Benign Prostatic Hyperplasia (BPH) Benign prostatic hyperplasia (BPH) is nonmalignant adenomatous overgrowth of the periurethral prostate gland. Symptoms are those of bladder outlet obstruction—weak stream, hesitancy, urinary... read more , 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 Erectile Dysfunction Erectile dysfunction is the inability to attain or sustain an erection satisfactory for sexual intercourse. Most erectile dysfunction is related to vascular, neurologic, psychologic, and hormonal... read more ).

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.