Action of catecholamines on exocrine pancreatic secretion of conscious rats

The effect of four different catecholamines (adrenaline, noradrenaline, isoprenaline and dopamine) were tested on the exocrine pancreatic secretion of conscious rats equipped with a pancreatic and biliary fistula, bile being continuously recirculated into the duodenum. Contrary to what has been observed in the anaesthetized animal neither of these four catecholamines had any stimulatory effect on volume. High bolus doses of adrenaline (440 microgram/kg) or noradrenaline (80 microgram/kg) or dopamine (10 mg/kg) inhibited volume and protein secretion probably by inducing strong vasoconstriction and anoxia. The infusion of high doses of dopamine (2.5 mg/kg/hr) induced a significant inhibition of volume and protein output. This inhibitory effect was neither modified by propranolol nor by haloperidol proving that it was a non specific effect secondary to the increase of vascular resistence. Isoprenaline either injected (125, 250 and 500 microgram/kg) or infused (25 microgram/kg/hr) induced an inhibition which was blocked by propranolol. It is suggested that in conscious rats, circulating catecholamines have probably a limited role in the control of pancreatic secretion although they could have some inhibitory action on protein secretion. Isoprenaline inhibits protein secretion probably by acting on a beta receptor mechanism. The pancreas of the rat does not seem to have stimulatory dopamine receptors.