Cardiovascular effects of delta9-tetrahydrocannabinol in conscious and anaesthetized dogs.

1. Temporal effects of delta9-tetrahydrocannabinol (THC) on heart rate and blood pressure in conscious dogs were compared to those in anaesthetized dogs. 2. In conscious dogs, THC in doses of 0.25 and 0.1 mg/kg resulted in maximal heart rate reductions of 48 and 41%, respectively, and in no significant change in blood pressure. 3. In anaesthetized animals THC in doses of 0.5 and 0.25 mg/kg caused a peak reduction in heart rate of 38 and 34%, and of blood pressure of 24 and 8%, respectively. 4. The results demonstrate that the bradycardia in response to THC in dogs is independent of the concomitant anaesthesia. 5. We conclude that the discrepancy between heart rate response to THC in dogs and in man is due to a species difference.