Physiology of the vas deferens.

Seminal emission occurs in response to rhythmic contractions of male secondary sex organs, including the vas deferens. Although contraction of the vas is directly due to adrenergic mechanisms, numerous substances modulate the release of norepinephrine from sympathetic pathways. These substances include local endogenous factors and neurotransmitters such as acetylcholine and NPY. Many substances are capable of altering the contractility of the vas deferens by modulating neural transmitter release or the basal tone of this smooth muscle. Because multiple pathways and substrates are capable of affecting its contractility, it is not surprising that drugs and metabolic disorders influence the function of the vas deferens and, ultimately, male fertility.