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The beta3-adrenoceptor-mediated relaxation induced by epinephrine in guinea pig taenia caecum
K Koike1, T Horinouchi, Y Yamamoto
1Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Funabashi, Chiba, Japan.
Abstract:
The mechanisms of the beta-adrenoceptor mediated relaxation induced by epinephrine in guinea pig taenia caecum were examined. The relaxant response to epinephrine was unaffected by propranolol (approximately 10(-5) M) or phentolamine (approximately 10(-5) M). The response to epinephrine was antagonized in a concentration dependent manner by bupranolol, and Schild plot of the data revealed the pA2 value of 5.87. Epinephrine significantly increased cyclic AMP level in this preparation. Bupranolol (10(-4) M) significantly decreased the cyclic AMP level that was elicited by epinephrine, whereas propranolol (10(-5) M) produced no effect. These results suggest that the relaxant response to epinephrine in the guinea pig taenai caecum is mainly mediated by beta3-adrenoceptors.
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