The mechanisms required for erection include nerve system, blood vascular system and endocrine system. Among them, the first two systems are especially important.The pelvic nerve accelerates erection.The hypogastric nerve suppresses erection and relates to ej aculation.Further, the NANC (non-adrenergic non-cholinergic) nervous system includ-ed in the cavernous nerve plays a key role in stimulating erection.Nitrogen monoxide (NO) is synthesized at the nerve ending.NO infiltrates the cavernous artery, spiral artery and smooth muscle and stimulates guanylate cyclase to produce cGMP from GTP.This cGMP combines to cGMP specific protein kinase to reduce the intracellular calcium concen-tration.Then, the cavernous artery, spiral artery and the smooth muscle of the trabeculae of corpus spongiosum are relaxed.The arterial blood flows into the sponge-like cavernous sinus to stimulate erection.

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Pharmacological characteristics of electrical field stimulation (EFS)-induced mechani-cal responses in the bovine uterus indicate smooth muscle layer-specific variations in autonomic innervation (exclusive adrenergic innervation in the longitudinal muscle and non-adrenergic, non-cholinergic (NANC) innervation in the circular muscle).The aim of the present study was to characterize the neurotransmitter of NANC nerves in the bovine uterus using functional and biochemical approaches.EFS of uterine circular muscle caused atropine and guanethidine-resistant contraction, which was abolished by tetrodotoxin.The EFS-induced contraction was not decreased by pyrilamine, methysergide or indomethacin.In the presence of atropine and guanethidine, bioactive peptides (angiotensin II, bombesin, calcitonin-gene related peptide, enkephalins, galanin, neurokinin A, neurokinin B, substance P, neurotensin, vasoactive intestinal polypeptide), ATP and 5-hydroxytryptamine did not produce contraction of the myometrium.An acid extract of the bovine uterus (EBU) contracted both guinea-pig ileum longitudinal muscle (GPILM) and bovine uterus.Neither tetrodotoxin nor methysergide decreased the EBU-induced contraction.Atropine and pyrilamine inhibited the EBU-induced responses, but some of the contractions (5-15%) were resistant to both antagonists.On a Sephadex G50 column, smooth muscle contracting material was eluted in one peak.Active fractions were pooled and applied to a Sephadex G25 column to compare the elution volume of the active material with those of peptides of known molecular weights.The active material was eluted in one peak and the molecular weight was estimated to be 1200.The gel-filtrated fraction induced contraction of both GPILM and bovine uterus, and its contractile activity was abolished by a-chymotrypsin.In conclusion, uterotonic peptide was discovered in extract of the bovine uterus and was thought to be one of transmitter for NANC nerves.However, further studies are needed to clarify the structure of this unknown peptide and its physiological roles.

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