Comparison of beta 1- and beta 2-adrenoceptor effects on gastric emptying of a fat meal in mice.

The effects of intraperitoneal administration of isoproterenol (a mixed beta 1- and beta 2-agonist), dobutamine (a selective beta 1-agonist) and clenbuterol (a selective beta 2-agonist) on gastric emptying were investigated in mice killed 30 min after gavage with a 51Cr radiolabeled milk meal. Administered 30 min prior to the meal, isoproterenol (2 mg/kg) and dobutamine (1 and 2 mg/kg) accelerated gastric emptying and clenbuterol (0.05 and 0.1 mg/kg) slowed it. The stimulation of gastric emptying by isoproterenol (2 mg/kg) and dobutamine (2 mg/kg) was blocked by the previous administration of either mixed beta 1- and beta 2-antagonist, propranolol (1 mg/kg), or a specific beta 1-antagonist, acebutolol (1 mg/kg). Only propranolol (1 mg/kg) antagonized the decrease of gastric emptying induced by clenbuterol. A high dose of propranolol (10 mg/kg), injected alone, reduced gastric emptying. It is concluded that the increase in gastric emptying caused by beta-adrenergic drugs is mediated through beta 1-adrenoceptors, while beta 2-receptors are involved in the inhibition of this function. The lack of effects of propranolol at doses able to block the action of beta 1- and beta 2-adrenoceptor agonists suggests that beta-adrenoceptors are not physiologically involved in the control of gastric emptying.