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. 1993 Aug;109(4):1079–1084. doi: 10.1111/j.1476-5381.1993.tb13732.x

Alpha 2-adrenoceptor-mediated modulation of the nitrergic innervation of the canine isolated ileocolonic junction.

G E Boeckxstaens 1, J G De Man 1, P A Pelckmans 1, A G Herman 1, Y M Van Maercke 1
PMCID: PMC2175751  PMID: 7691364

Abstract

1. The effects of specific alpha-adrenoceptor agonists and antagonists on electrically-evoked non-adrenergic non-cholinergic (NANC) relaxations, previously demonstrated as nitrergic, were investigated in isolated circular muscle strips of the canine ileocolonic junction. 2. During a substance P-induced contraction and in the presence of atropine and guanethidine, the specific alpha 1-adrenoceptor agonist, phenylephrine and antagonist, prazosin, as well as the specific alpha 2-adrenoceptor antagonist, yohimbine, had no effect on the NANC relaxations evoked by electrical field stimulation. In contrast, clonidine and the more specific alpha 2-adrenoceptor agonist, UK-14,304, significantly reduced the electrically-induced relaxations, preferentially those in response to low frequency stimulation. The inhibitory effect of UK-14,304 on these relaxations was antagonized by yohimbine. 3. During a noradrenaline-induced contraction, clonidine, but not UK-14,304 significantly augmented the relaxations to electrical stimulation. 4. The adrenoceptor agonists and antagonists used had no effect on concentration-response curves to NO or on the relaxation induced by nitroglycerin. 5. These results indicate that stimulation of prejunctional alpha 2-adrenoceptors inhibits the nitrergic NANC relaxations induced by field stimulation and thus suggest prejunctional regulation of nitric oxide release via alpha 2-adrenoceptors in the canine ileocolonic junction.

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Selected References

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