Adult: Initially, 150-250 mcg/kg; additional doses of 30 mcg/kg may be given as needed.

Left atria were mounted in organ baths containing 20 ml of oxygenated Tyrode’s solution. The preparations were preloaded with 5 millinewton and electrically stimulated via platinum contact electrodes at 3 Hz with rectangular pulses of 5-ms duration. The voltage was 1.5-fold over the threshold of excitation amounting to about 2 V. Contraction force (CF) was recorded isometrically. After an equilibration period of 60 min, a cumulative concentration/effect curve for the negative inotropic action of the agonist under study was recorded. Each agonist concentration was applied for 10 min, a period sufficient to obtain equilibrium effects. Contraction force was expressed as the percentage of the value found at the end of the equilibration period. The agonist was removed from the organ bath over a period of 30 min by replacing the Tyrode’s solution with fresh solution every 10 min. Thereafter, the preparation was preincubated with the Alcuronium for 60 min before another agonist concentration/effect curve was measured in the presence of the Alcuronium. Contraction force was expressed as the percentage of the value at the end of the preincubation period with the Alcuronium. The agonist was washed out using Tyrode’s solution still containing the Alcuronium in the concentration as before. After 30 min of washout, the concentration of the Alcuronium was increased, and, after a preincubation phase of 60 min, another concentration/effect curve of the agonist was measured.