Some observations on the gastric effects of phentolamine in rats.

The effects of graded doses of phentolamine on gastric secretion, gastric emptying rate, gastric mucosal mucus content and gastric mucosal lesion incidence were studied in conscious rats 2 h after intramuscular administration. In pylorus-occluded rats, phentolamine (5, 10 or 20 mg/kg) produced dose-dependent decreases in the gastric secretory volume and total acid output. Similar doses of the drug also produced dose-dependent decreases in the gastric emptying rate in animals without pylorus occlusion (intact rats), but did not affect the gastric mucosal mucus content. The incidence of gastric mucosal lesions in pylorus-occluded or intact animals rose with increasing doses. The findings are discussed in the light of the possibility that phentolamine, in the dose range examined, possesses a sympathomimetic action which would underlie the gastric lesions observed.