Effects of L-NG-nitro-arginine on noradrenaline induced contraction in the rat anococcygeus muscle |
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Authors: | Yolanda Hoyo Jesús Giraldo Elisabet Vila |
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Affiliation: | Departament de Farmacologia i Terapèutica, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain;*Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain |
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Abstract: | - The influence of L-NG-nitro-arginine (L-NOARG, 30 μM) on contractile responses to exogenous noradrenaline was studied in the rat anococcygeus muscle.
- Noradrenaline (0.1–100 μM) contracted the muscle in a concentration-dependent manner. L-NOARG (30 μM) had no effect on noradrenaline responses.
- Phenoxybenzamine (Pbz 0.1 μM) depressed by 46% (P<0.001) the maximum response and shifted to the right (P<0.001) the E/[A] curve to noradrenaline (pEC50 control: 6.92±0.09; pEC50 Pbz: 5.30±0.10; n=20).
- The nested hyperbolic null method of analysing noradrenaline responses after phenoxybenzamine showed that only 0.61% of the receptors need to be occupied to elicit 50% of the maximum response, indicating a very high functional receptor reserve.
- Contractile responses to noradrenaline after partial α1-adrenoceptor alkylation with phenoxybenzamine (0.1 μM) were clearly enhanced by L-NOARG.
- The potentiating effect of L-NOARG on noradrenaline responses after phenoxybenzamine was reversed by (100 μM) L-arginine but not by (100 μM) D-arginine.
- These results indicate that spontaneous release of NO by nitrergic nerves can influence the α1-adrenoceptor-mediated response to exogenous noradrenaline.
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Keywords: | Anococcygeus muscle (rat), α 1-adrenoceptor, L-NG-nitro-arginine, NANC transmission |
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