The pharmacological perspective: role for the sympathetic nervous system in micturition and sexual function

Abstract

The predominant effects of the sympathetic innervation of the lower urinary tract in man are mediation of contraction of the bladder base and the urethra and inhibition of the parasympathetic pathways at spinal and ganglion levels. Sympathetic tone also mediates the contractility of smooth muscle fibres in the prostatic stroma, and it has an important role in maintaining the penis in a flaccid state and in ejaculation. In the detrusor muscle of most species, β-adrenoceptors (β-ARs) mediating relaxation normally dominate over α-ARs mediating contraction, and the effect of noradrenaline (NA) is relaxation. The human detrusor is able to express β₁-, β₂- and β₃-ARs and stimulation of β₃-ARs causes relaxation. Low, but reproducible expression of α₁-ARs (α_1a and α_1d) has been found in human detrusor muscle, but the α₁-AR subtypes mediating contraction have not been established. The sympathetic pathways to the penis may mediate anti-erectile as well as erectile effects. Although α₁ and α₂-ARs have been demonstrated in human corpus cavernosum tissue, available information supports the view of a functional predominance of α₁-ARs. The human vas deferens also has an important adrenergic innervation and α_1A-ARs seem to mediate contraction.