Fig. 7. (A) Evidence of synergism between 10 µmol l^–1 8-bromo cyclic AMP (cAMP) and 0.3 µmol l^–1 Tenmo-ADFb (ADFb). Bars represent the means + 1 s.e.m. for the change in rate of secretion ( pl mm^–1 min^–1) following addition of the secretagogues individually and together. The number of replicates is shown in parentheses, and identical letters indicate values that differ significantly (P<0.001). The sum of the separate responses to 8-bromo cyclic AMP and Tenmo-ADFb (Sum) is significantly less than when they are tested together (Both). (B) 8-bromo cyclic GMP (1 mmol l^–1) increases secretion by tubules that have been maximally stimulated by Tenmo-ADFb (10 µmol l^–1) and Achdo-KII (1 nmol l^–1; AKII). Bars represent the means + 1 s.e.m. for the change in rate of secretion ( pl mm^–1 min^–1) after addition of the peptides alone (open bars) and then together with 8-bromo cyclic GMP (grey bars). Black bars show the diuretic activity of 1 mmol l^–1 8-bromo cyclic GMP alone measured in separate groups of tubules. The number of replicates is shown in parentheses, and identical letters indicate values that differ significantly (P<0.001).