Rats (n ϭ 10) were used. The animals were anesthetized with sodium pentobarbital (30 mg·kg Ϫ1 ) intraperitoneally. After tracheotomy, cannulation of the jugular vein and the carotid artery was performed for injection of drugs and to record the mean arterial blood pressure (MAP), respectively. Preliminary studies were done to determine the doses. The injected doses were: 27.29µM of epinephrine, 4.80 µM of felypressin, and a combination of 27.29 µM of epinephrine plus 4.80 µM of felypressin. The substances were prepared with serum. Epinephrine and felypressin were administered by i.v. injection of 0.2 ml, and the combination by i.v. injection of 0.4 ml, both followed by injection of 0.2 ml of serum to flush the residual. The interval between administrations was 15 min, and the rate of administration was 0.2 ml per 5 s. The hemodynamic variables stabilized, on average, 15 min after the end of the preparation. The sequence of application of the doses was drafted before each experiment. MAP was recorded with a transducer TBS 104A, coupled to a BIOPAC SYSTEM Model MP100 (Santa Barbara, CA, USA). An electrocardiograph ECG-4-FUNBEC (São Paulo, Brazil) was used to record the heart rate (HR). The electrocardiogram was evaluated in D2 derivation (with the negative electrode on the right front leg and the positive electrode on the left rear leg). The records were made before and 15 s after administration of the substances, at the time of the highest effect. The results were analyzed by ANOVA (Student-Newman-Keuls), with P Ͻ 0.05 indicating statistical significance.

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