A new method to evaluate cardiovascular response in anesthetized rats. Hypertension after variable intensity, brief electrical stimuli.

To establish and standardize a nociceptive response in anesthetized rats, the hypertensive responses to defined electrical and mechanical stimuli were studied. Rats (n = 7) were given etomidate, 3.8 mg/kg/hr intravenously (i.v.) 2 hr following carotid artery and jugular vein cannulation. At 15 min after beginning the infusion, four types of noxious stimuli were administered sequentially at 1-min intervals (14 stimuli total): Type 1: Square electrical waves, 125 cps, 1.6 msec, 2-sec train duration, varying current from 0.4 to 12 mA (11 stimuli); Type 2: A single 10-mA electrical stimulus, 5-sec train duration; Type 3: Tail clamping; and, Type 4: Skin incision. After each stimulus, maximum change in systolic blood pressure (delta SBP) was measured. delta SBP after the most intense stimuli was as follows: Type 1 (12 mA, 2 sec), 32.1 +/- 2.14 mmHg; Type 2 (10 mA 5 sec), 42.9 +/- 2.4 mmHg; Type 3 (tail-clamping), 34.3 +/- 3.3 mmHg; Type 4 (skin incision), 14.2 +/- 2.8 mmHg. For the multiple Type-2 stimuli, a relationship between current and delta SBP was present. The authors believe that characterized graded electrical stimulation will allow a more quantitative evaluation of the hypertensive response to noxious stimuli in etomidate anesthetized rats, as compared to observing a single response to a single stimulus. The characterization of the electrical stimulation by amplitude, frequency, and wave form makes research work on nociception under anesthesia easily reproducible.