veratrine and Apnea

With cats anaesthetized with sodium pentobarbital we studied how veratrine-induced reflexes interact with cough. Cough was elicited by mechanical stimulation of tracheobronchial mucosa and its intensity was evaluated from the changes in oesophageal pressure. Veratrine injected intravenously produced apnoea, bradycardia and long-lasting hypotension. With each dose the intensity of cough was significantly decreased during the apnoea. When the mechanical stimulus was repeated during the breathing following apnoea with remaining hypotension, cough intensity parameters were not changed from control. Veratrine injected intracardially caused bradycardia, hypotension, and decreases in respiratory rate and tidal volume. The intensity of cough elicited just after injection of veratrine was also significantly decreased. We suggest that veratrine-induced reflexes depress the cough reflex mainly by inhibitory reflexes arising from cardiac receptors. The inhibition of cough is probably mediated indirectly via the inhibition of medullary respiratory neurons.

Topics: Animals; Apnea; Bradycardia; Cats; Cough; Dose-Response Relationship, Drug; Female; Heart; Hypotension; Injections, Intravenous; Male; Reflex; Veratrine

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)

Topics: Animals; Apnea; Blood Pressure; Bradycardia; Drug Synergism; Electrocardiography; Heart Rate; Heart Ventricles; Hypotension; Injections; Injections, Intra-Arterial; Injections, Intravenous; Male; Rats; Reflex; Respiration; Scorpion Venoms; Vagotomy; Veratridine; Veratrine

Topics: Apnea; Cell Respiration; Diphenhydramine; Injections, Intravenous; Respiration; Veratrine