Abstract
The mechanisms of the β-adrenoceptor-mediated relaxation induced by epinephrine in guinea pig taenia caecum were examined. The relaxant response to epinephrine was unaffected by propranolol (∼10-5M) or phentolamine (∼10-5M). 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 (10-4M) significantly decreased the cyclic AMP level that was elicited by epinephrine, whereas propranolol (10-5M) produced no effect. These results suggest that the relaxant response to epinephrine in the guinea pig taenai caecum is mainly mediated by β3-adrenoceptors.
