A novel neurogenic vasodilator mechanism in bovine mesenteric artery.

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Abstract
The presence of a neurogenic vasodilator mechanism was investigated in isolated bovine mesenteric arteries (BMAs) that were precontracted with phenylephrine. Electrical field stimulation induced tetrodotoxin-sensitive relaxations in guanethidine-pretreated BMAs. The relaxation occurred after a delay of about 5-8 seconds and amounted to 25-35% in different sets of experiments. The relaxation was not affected by classical receptor antagonists such as atropine (1 microM), cimetidine (3.9 microM), clemastine (2.8 microM), naloxone (1.2 microM), 8-phenyltheophylline (1 microM), propranolol (3.4 microM), ritanserin (5 microM), or droperidol (13 microM). The nicotinic acetylcholine-receptor stimulant 1,1-dimethyl-4-phenyl-piperazinium iodide (10 microM) was without effect on the relaxation, and removal of the endothelium of the arteries also had no effect. The bee venom component apamin (1 microM), which has been shown to block the nonadrenergic, noncholinergic relaxation in intestinal and vascular smooth muscle from other species, was also found to be without effect on the relaxation induced by electrical field stimulation in BMAs. Pretreatment of the arteries with capsaicin (1 microM) had no effect per se and did not affect the relaxation induced by a subsequent stimulation. Capsaicin has been suggested to release neurotransmitter and eventually deplete neurons containing substance P and calcitonin gene-related peptide. Furthermore, exogenously applied calcitonin gene-related peptide (1-100 nM), substance P (10 nM-1 microM), and vasoactive intestinal peptide (0.3-30 nM) gave relaxations amounting to less than 10%. It is postulated that electrical field stimulation induces a neurogenic relaxation of a nonadrenergic, noncholinergic nature in BMAs.(ABSTRACT TRUNCATED AT 250 WORDS)