THE LACK OF β-ADRENOCEPTOR INVOLVEMENT IN THE CARDIAC ACTION OF Δ1-TETRAHYDROCANNABINOL IN RATS

1. Rat isolated hearts perfused with Δ¹-THC (0·5 μ/ml) showed a reduction in the rate of beating which was not altered by pretreatment with propranolol (2 μg/ml), atropine (4 μg/ml) or hexamethonium (4 μ/ml). 2. Propranolol (2 μg/ml) also caused a decrease in the rate of beating, which was not affected by pretreatment with Δ¹-THC (0·5 μg/ml). 3. In pithed rats, propranolol (2 mg/kg, i.v.) caused a decrease in the pulse rate, which was not altered by prior administration of Δ¹-THC (1 mg/kg, i.v.). 4. In both preparations, the responses to isoprenaline were markedly reduced or abolished by propranolol, but they were unaffected by Δ¹-THC. 5. It is concluded that the hypotensive and cardiac slowing actions of Δ¹-THC are not mediated by activation of parasympathetic nerves or by β-adrenoceptor blockade.