Involvement of β1-and β2-but not β3-adrenoceptor activation in adrenergic PYY secretion from the isolated colon

The secretion of PW by endocrine L cells of the terminal gut is under the control of nutrients, the autonomic nervous system and hormones. Catecholamines, and the non-specific beta -adrenergic agonist isoproterenol induce PW secretion from rat isolated colon or ileum. Because beta3-adrenergic receptors now appear to mediate many of the effects of catecholamines in the gastrointestinal tract, we investigated the involvement of beta1-, beta2-, and beta3-adrenoceptor stimulation in PW secretion from the isolated, vascularly perfused rat colon. Infusion of 10(-6) M isoproterenol induced a transient increase in PW secretion (from 36 +/- 4 to 87 +/- 20 fmol/2 min; n=7, P<0.05), that was abolished by a previous infusion of the <beta>1- and beta2-adrenergic blocker (and partial beta3-agonist) alprenolol (10(-6) M). The beta1-adrenergic agonist dobutamine and the beta -2 agonist terbutaline also (both at 10(-5) M) significantly stimulated PW secretion, from 29 +/- 1 to 79 +/- 12 fmol/2 min and from 19 +/- 1 to 73 +/- 13 fmol/2 min respectively (n=7, P<0.05). Neither of the <beta>3- adrenergic agonists tested (BRL 37 344 (10(-5), 10(-6) M) and SR 58 611A (10(-6) M)) significantly stimulated PW secretion, thus confirming the exclusive involvement of beta1- and beta2-receptors in beta -adrenergic agonist induced hormone secretion.