Different effect of glucagon on gastric acid secretion in vivo and in vitro

The effect of glucagon on gastric acid secretion was evaluated in conscious cats with gastric fistula and in the isolated gastric fundus from immature rats. Glucagon (10-25 micrograms/kg/h) caused a slight inhibitory effect on pentagastrin-induced acid secretion; in contrast it was ineffective against dimaprit. At these doses glucagon induced a marked increase in glucose plasma levels. In the isolated rat gastric fundus glucagon (10(-7) M-3 x 10(-6) M) induced a concentration-dependent increase in acid output, being approximately 100 times as potent as histamine. Conversely from histamine, glucagon was not affected by pretreatment with phosphodiesterase inhibitors, thus an involvement of cAMP seems to be unlikely.