Influence of CGP 12177, DMB, BK-21, BK-22, BK-23 and BK-25 on HR (a) and their interaction with CGP 20712 and ICI 118,551 (b). Experiments were performed in pithed and vagotomized rats. Each dose of agonist was studied in separate rats. In some cases, the two lower doses were applied to one animal. The first or only dose was given 5 min after injection of vehicle (CON) or CGP 20712 given in combination with ICI 118,551 (0.1 μmol kg−1 each). Means of 3–13 rats. **P<0.01; ***P<0.001 compared to the corresponding CON. For some data points, s.e.m. is contained within the symbol.