The effect of sympathomimetic agents on gastric acid secretion in rats

Beta-adrenoceptor agonists have been reported to inhibit gastric acid secretion in vivo but their site and mode of action is uncertain. A study of the effects of such agents on acid secretion in the rat has been made using both an in vivo preparation and an in vitro one where possible effects due to neural, hormonal or cardiovascular actions of beta-agonists are avoided. In conscious rats with Heidenhain pouches, isoprenaline (40 micrograms kg-1h-1) inhibited the response to pentagastrin (20 micrograms kg-1h-1). This inhibition was abolished by propranolol (2 mg kg-1) and butoxamine (8 mg kg-1) and partially reversed by practolol (8 mg kg-1). Propranolol alone (2 mg kg-1) significantly increased the response to pentagastrin in the pouch rats but butoxamine and practolol (both at 8 mg kg-1) and the inactive isomer (+)-propranolol were without effect on the pentagastrin response. In the rat isolated stomach preparation isoprenaline, salbutamol, salmefamol , adrenaline and nor-adrenaline all stimulated acid output over the range 2 X 10(-7) to 10(-5)M. These responses were antagonised by propranolol (2 X 10(-5)M), pindolol and timolol (10(-6)M) but only nor-adrenaline stimulated secretion was inhibited by the selective antagonists practolol, atenolol, butoxamine and ICI 118551. In vitro responses to beta-adrenoceptor agonists were not antagonised by atropine (10(-5)M), metiamide (10(-4)M) or prostaglandin E2 (10(-5)M).(ABSTRACT TRUNCATED AT 250 WORDS)