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

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Abstract
Differences in sensitivity to catecholamines between colon and duodenum were examined in tissues from the rat, monitoring the depressive effect of catecholamines 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[c]AMP (10-4 g/ml) depressed the contractile responses of both tissues to ACh. After treatment with Ep (10-7 g/ml), cAMP content was increased in the colonic tissue but not in the duodenal. Papaverine (3 .times. 10-6 g/ml) and a higher dose of Ep (10-6 g/ml) increased cAMP content in both tissues. The increase of cAMP and the decrease of tension caused by Ep were not correlated in these tissues. A positive correlation was observed between the depressive effect of Ep on the contractile response to ACh and the increase of cAMP content in these tissues.
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