The Bezold-Jarisch-like effect induced by veratridine and its potentiation by scropion toxin in the rat.

The Bezold-Jarisch-like effect (BJE) induced by 2.5 micrograms/100 g of veratridine injected intravenously or into the left ventricle was studied in anesthetized rats. The possible potentiation of the effect by a small dose (10 micrograms/100 g) of a purified scorpion toxin (tityustoxin) was also investigated. Heart rate (HR), electrocardiogram (ECG), mean arterial pressure (MAP) and respiratory rate (RR) were recorded. Intravenous (iv) injection of veratridine induced a BJE consisting of slight bradycardia in 4 out of 8 experiments, fall of MAP (from 107 +/- 3 to 90 +/- 4 mmHg) and apnea. The control RR was 105 +/- 5 insp/min and apnea, after veratridine, lasted 8 +/- 2 s. The BJE evoked by injection of a second dose of veratridine was potentiated 20 min after an iv injection of tityustoxin. The HR decreased from 334 +/- 16 to 108 +/- 17 beats/min, the MAP fell from 110 +/- 5 to 68 +/- 4 mmHg and the control RR of 92 +/- 5 insp/min was followed by a long period of apnea (68 +/- 17 s). Injection of veratridine into the left ventricle (lv) evoked a BJE characterized by slight bradycardia in 5 out of 10 experiments, arterial hypotension (from 110 +/- 6 to 89 +/- 6 mmHg) and tachypnea (from 82 +/- 6 to 102 +/- 7 insp/min). The effects induced by a second dose of veratridine were potentiated 20 min after an lv injection of tityustoxin. The HR decreased from 377 +/- 14 to 119 +/- 18 beats/min, the MAP fell from 119 +/- 5 to 72 +/- 10 mmHg and the RR increased from 80 +/- 6 to 117 +/- 9 insp/min. This tachypnea was followed by bradypnea 20 s later (21 +/- 6 insp/min). The ECG showed that hypotension induced by iv or lv injections of veratridine coincided with a slight sinus bradycardia before tityustoxin (N = 9) and A-V block after the toxin (N = 18). Cervical bilateral vagotomy prevented the cardiac and respiratory effects induced by lv veratridine in tityustoxin-treated rats, but a slight hypotension was still recorded (from 114 +/- 10 to 94 +/- 10 mmHg, P less than 0.05). Injection of veratridine (2.5 micrograms/100 g) into the ascendent aorta evoked a slight hypotension (from 105 +/- 6 to 87 +/- 7 mmHg, P less than 0.05) and tachypnea followed by bradypnea, but bradycardia was not recorded.(ABSTRACT TRUNCATED AT 400 WORDS)