Effect of glucagon on gastric acid secretion by the isolated fundus from immature rats

The effect of glucagon was studied on the isolated gastric fundus from immature rats in comparison with histamine. Glucagon (10^–7–3×10^–6M) caused a concentration-dependent increase in acid output, being approximately 25 fold more potent than histamine (ED₅₀ values were 6.38×10^–7M and 2.42×10^–5M for glucagon and histamine, respectively). These compounds, however, did not differ in regard to the maximum response. The stimulatory effect of glucagon was not enhanced by pretreatment with 3×10^–8M forskolin or 10^–7M ICI 63197, a phosphodiesterase (PD) inhibitor. Conversely, both forskolin and ICI 63197 shifted to the left the concentration-response curve to histamine. The increase in acid secretion by glucagon was reduced by PGE₁ (10^–5M) and PGE₂ (10^–5M) but only PGE₂ inhibited the response to histamine. From these data it can be concluded that glucagon stimulated acid production in the stomach from immature rats, and this effect does not seem to involve the same adenylate cyclase activated by histamine.