Circulating endocannabinoid concentrations during orthostatic stress.

Background: In animals, the endocannabinoid system is activated during hemodynamic insults and restrains blood pressure in part through sympathetic inhibition.
Materials and Methods: We tested the hypothesis that hemodynamic stress elicited by head-up tilt testing increases systemic endocannabinoid concentrations in humans and that excessive endocannabinoid availability predisposes to presyncope.
Results: With head-up tilt, 2-arachidonoylglycerol increased, whereas anandamide remained unchanged.
Conclusions: In contrast to our expectations, anandamide plasma concentration at rest was directly correlated with orthostatic tolerance, rather than intolerance.