The Bioassay of Cannabinoids Using the Mouse Isolated Vas Deferens

The mouse isolated vas deferens is a nerve-smooth muscle preparation that serves as a highly sensitive and quantitative functional in vitro bioassay for cannabinoid CB₁ receptor agonists. Additionally, it is commonly used as a bioassay for competitive surmountable CB₁ receptor antagonists, and also provides a means for distinguishing neutral CB₁ antagonists from CB₁ inverse agonists. The bioassay of CB₁ receptor agonists relies on the ability of these ligands to produce concentration-related decreases in the amplitude of electrically evoked contractions of the vas deferens. This they do by acting on naturally expressed prejunctional neuronal CB₁ receptors to inhibit release of the contractile neurotransmitters, noradrenaline and ATP, that is provoked by the electrical stimulation. The bioassay of competitive surmountable CB₁ receptor antagonists involves determining the ability of these compounds to produce parallel dextral shifts in CB₁ receptor agonist log concentration-response curves in electrically stimulated tissues. The mouse vas deferens has also been used to measure the ability of anandamide to activate vanilloid (TRPV1) receptors, to monitor modulation by cannabinoids such as 6″-azido-2″-yne and abnormal cannabidiol of contractions elicited in electrically unstimulated tissues by agonists for P2X purinoceptors or α₁ -adrenoceptors, and as a bioassay for the nonpsychoactive plant cannabinoid cannabidiol.