Fig. 2. Time-course for cyclic AMP production in response to (A) forskolin (10 µmol l^–1) and (B) theophylline (3 mmol l^–1) in the duodenal mucosa of Gallotia galloti. Forskolin and theophylline were added at time zero. Each point represents the mean ± S.E.M. for six separate determinations. *P<0.05; **P<0.01 compared with time 0.