Inhibition of exocrine pancreatic secretion by alpha-adrenergic blocking agents in conscious rats

The effects of the alpha-adrenergic blocking agents, phentolamine and phenoxybenzamine were tested on the exocrine pancreatic secretion of conscious rats. Phentolamine (0.156 mg/kg to 1.25 mg/kg) and phenoxybenzamine (1.25 and 2.5 mg/kg) strongly inhibited basal volume and protein secretion. On the other hand, phentolamine had no effect on the cholecystokinin-pancreozymin or urecholine stimulated exocrine pancreatic secretion. The infusion of phentolamine (1.25 mg/kg/hr) greatly impaired the stimulatory effect on protein secretion induced by soybean trypsin inhibitor and oleic acid. These experiments suggest that alpha-adrenergic blocking agents inhibit pancreatic secretion of the conscious rat by impairment of cholecystokinin-pancreozymin release either by a direct inhibitory action or by blocking a still unknown alpha-adrenergic stimulatory reflex present in the duodenal mucosa.