Abstract: The response of the gastrointestinal smooth muscle to adrenergic stimulation was studied in Muscovy duck (Cairina moschata). Adrenergic stimulation was achieved by application of adrenaline on strips of isolated duodenum in organ bath. The potency, affinity and efficacy of the agonist alone and in the presence of antagonists were determined by EC₅₀, pA₂ and Emax, respectively. Adrenaline inhibited contractions of the smooth muscle of the gastrointestinal tract of C. moschata in a dose dependent fashion. Contractions of isolated duodenum recorded in the presence of adrenaline were predominantly of slow wave components. The cumulative concentration-response curve revealed that there were two phases of the response of duodenum to adrenaline. There was an initial concentration-dependent contraction of partially contracted segments from 1�10 ⁹-1�10 ⁷M of adrenaline, while concentrations higher than 1�10 ⁷ M caused relaxation. Dibenamine and propranolol modified the response of duodenum to adrenaline and caused a rightward shift of adrenaline cumulative concentration-response curve in the isolated duodenum which indicate the presence of a- and - receptors as mediators of adrenergic effects. Both antagonists significantly (p< 0.05) reduced the potency (EC₅₀) of adrenaline. The pA₂ value was also reduced in the presence of dibenamine (p>0.05) and propranolol (p< 0.05) which indicated a reduction in the affinity of adrenaline for the receptors. Dibenamine caused 85% reduction of maximal relaxant response of duodenum to adrenaline; this depression was statistically significant (p< 0.001). Pretreatment of the tissue with propranolol however caused a non-significant (p>0.05) depression of maximal response of duodenum to adrenaline. These all points to the fact that while dibenamine inhibits adrenaline non-competitively, propranolol acts as a competitive blocker. The study confirms that pharmacological responses to adrenergic stimulation in the gastrointestinal tract of C. moschata are mediated by a- or - adrenergic receptors. This effect could be inhibitory or stimulatory depending on the dose of adrenaline administered. It was therefore concluded that the dose of catecholamines modulate what receptor is predominantly stimulated in a tissue at a particular time.