DEPRESSIVE EFFECT OF EPINEPHRINE MEDIATED VIA ADRENERGIC BETA-RECEPTOR IN ISOLATED RAT COLON AND DUODENUM

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Differences in sensitivity to catecholamines between colon and duodenum were examined in tissues from the rat, monitoring the depressive effect of catecholamilies on contractile response to acetylcholine (ACh). The sensitivity of colonic tissue to ACh was higher than that of duodenal. Epinephrine (Ep, 10-7 g/ml) depressed the contractile response to ACh in the colonic tissue, but not in the duodenal. The depressive effect of Ep on the contractile response to ACh is attributed to the stimulation of adrenergic beta-receptors in the colonic tissue as the depression disappeared by pretreatment with propranolol (10-6 g/ml). There was no difference on the depressive effect of papaverine on the contractile response to ACh, except when low concentrations were used. Dibutyryl cyclic AMP (10-4 g/ml) depressed the contractile responses of both tissues to ACh. After treatment with Ep (10-7 g/ml), cyclic AMP content was increased in the colonic tissue but not in the duodenal. However, papaverine (3×10-6 g/ml) and a higher dose of Ep (10-6 g/ml) increased cyclic AMP content in both tissues. The increase of cyclic AMP and the decrease of tension caused by Ep were not correlated in these tissues. However, a positive correlation was observed between the depressive effect of Ep on the contractile response to ACh and the increase of cyclic AMP content in these tissues.
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