BACKGROUND

In animals, the endocannabinoid system is activated during hemodynamic insults and restrains blood pressure in part through sympathetic inhibition.

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.