THC Blood-Pressure Tolerance Depended on the Nervous-System Preparation in Rats
A 1981 rat experiment found that tolerance to selected THC cardiovascular effects depended on whether central nervous-system function was preserved. Blood-pressure and heart-rate responses also adapted differently.
The repeated exposure preceded an acute challenge
Rats received daily THC or vehicle before an intravenous THC challenge. Under urethane anesthesia, prior THC reduced the challenge's blood-pressure-lowering response but not its cardiac-slowing response. Vehicle-treated comparisons did not show the same adaptation.
A preparation change altered the finding
In pithed preparations, the cardiovascular challenge responses did not show the same treatment-history differences. Tolerance to THC enhancement of noradrenaline-induced pressor responses likewise appeared in anesthetized animals with intact central pathways but not in pithed animals. This comparison supported a central contribution under the protocol.
Heart rate did not stand in for blood pressure
The preserved cardiac-slowing response despite reduced depressor effects shows endpoint selectivity. These laboratory measures should not be combined into a single statement that cardiovascular tolerance developed or failed to develop across the whole system.
The authors concluded that intact central nervous-system function was required for the reported forms of tolerance. This finding cannot be transferred directly to awake humans or used to infer clinical cardiovascular safety. Anesthesia, preparation, challenge route and the specific response all define the evidence.
Related: interpreting cannabis tolerance claims.
Research cited
Li DM. Tolerance to the effects of delta 1-tetrahydrocannabinol on the pressor responses to noradrenaline in rats. Clinical and experimental pharmacology & physiology (1981). doi:10.1111/j.1440-1681.1981.tb00140.x. Findings discussed from the study abstract.
