Effect of acute administration of delta 1-tetrahydrocannabinol on beta-endorphin levels in plasma and brain tissue of the rat.

Acute treatment with delta 1-tetrahydrocannabinol (delta 1-THC) elevated the concentration of beta-endorphin-like immunoreactivity (beta-ELIR) in plasma and in the hypothalamus, but not in the hippocampus of rats habituated to the injection procedure. These effects were not obtained with the psychotropically inert analog of delta 1-THC, cannabidiol. In animals that had not been habituated to the injection procedure, placebo treatment induced a decrease in hippocampal beta-ELIR.