Adrenoceptors mediating relaxation to catecholamines in rat isolated jejunum

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Abstract
1 The characteristics of adrenoceptors mediating relaxation to catecholamines in rat isolated jejunum were investigated. 2 Catecholamines and BRL 37344 produced relaxation of the KCl-contracted strips with an order of potency of isoprenaline (1.0) > BRL 37344 (0.63) > noradrenaline (0.1) > adrenaline (0.04). 3 In the presence of both prazosin (1 μm) and propranolol (1 μm) only small dextral shifts of the concentration-response curves to agonists were observed and an order of potency of BRL 37344 (2.5) > isoprenaline (1.0) > noradrenaline (0.2) > adrenaline (0.1) was obtained. 4 In the presence of prazosin (1 μm) and propranolol (1 μm), cyanopindolol (0.1 − 10 μm) produced a concentration-dependent rightward shift of the concentration-response curve to adrenaline with a Schild slope not significantly different from unity and a mean pA2 value of 7.01. 5 The resistance of relaxant responses to propranolol, the relatively high potency of BRL 37344 compared to catecholamines and the competitive antagonism of relaxant responses to adrenaline by cyanopindolol suggest that β-adrenoceptors in rat small intestine are mainly atypical in nature.

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