The effects of adrenalectomy on the cardiovascular responses to delta 1-tetrahydrocannabinol in rats.

1. In urethane anaesthetized sham-operated rats, intravenous administration of delta 1-THC (1 mg/kg) caused an immediated and prolonged fall in blood pressure, with a concomitant reduction in pulse rate. 2. In rats which had been adrenalectomized 24 h previously, delta 1-THC (1 mg/kg, i.v.) also caused a depressor response, but it was significantly shorter in duration than that observed in sham-operated animals. The durations of the cardiac slowing effect were similar in both groups of rats. 3. Hydrocortisone pretreatment (25 microgram/kg, i.v.), given 45 min before delta 1-THC, restored the duration of the depressor response to delta 1-THC in adrenalectomized rats, but it did not have any effect on the bradycardia induced by delta 1-THC. 4. Hydrocortisone did not produce any significant effect on the hypotensive action of delta 1-THC in sham-operated rats, but the cardiac slowing effect was markedly potentiated. 5. These results suggest a lack of correlation between the hypotensive and cardiac slowing actions of the drug and that a certain level of adrenal steroids is necessary for the maintenance of the depressor response to delta 1-THC.