Cannabidiol and cannabigerol inhibit spontaneous contractions in the mouse isolated uterus

Background and Purpose: The production of endocannabionoids andthe presence of cannabinoid receptors in mouse uterus havepreviously been reported (Pagano et al., 2017). Furthermore, we havereported how uterine tissue harvested from early gestation mice (5–-9 days) spontaneously contracts when bathed in a high Ca2+(1.5 mM)containing physiological solution (Francis et al., 2003). In this study,we investigate the effect of the phytocannabinoids cannabidiol (CBD)and cannabigirol (CBG) on these contractions. Experimental Approach: Uterine horns were harvested from pregnantmice (C57BL6 strain; 5–9 days of gestation) and incubated at 37 C0 10-ml organ bath with modified De Jalon's solution containing2.5-mM Ca2+aerated with 95% O2/5% CO2. Spontaneous contrac-tions commenced and were allowed to equilibrate for 30 min beforedrug additions. Studies were performed in accordance with the Ani-mals (Scientific Procedures) Act 1986/ASPA Amendment Regulations2012. All drugs were obtained from Tocris and dissolved in DMSOwith the final concentration of DMSO in the bath being less than0.01% v/v. All control data were obtained in the presence of thecorresponding percentage DMSO (% v/v). Recordings were capturedusing Labchart 8 (ADI; V8.13) and analysed by measuring the AUC (g.s) using the integral relative to minimum method to take into accountchanges in both force and frequency of contraction. Cumulative addi-tions of drugs (concentration range 10−10to 10−5M) were madeevery 20 min, and the AUC was measured during the final 10 min ofeach addition. Uterine tissue was also harvested following in vivo per-fusion, and the location of CB1receptors was identified using immu-nohistochemistry and laser scanning confocal microscopy. Key Results: The non-psychoactive phytocannabinoids CBD and CBGproduced a concentration-dependent inhibition of spontaneous con-tractions with IC50s of 421 and 15.5 nM, respectively (n =6–9). Fur-thermore, the fatty acid amyl hydrolase (FAAH) inhibitor JNJ1661010also produced a concentration-dependent inhibition of spontaneouscontractions with an IC50of 367 nM. Finally, the CB1and GPR55receptor antagonist AM251 (Tocris) inhibited the effects ofJNJ1661010 with a pA2of 9.036 and a slope of 0.969. Finally, CB1receptors appear to be located within both circular and longitudinalmurine uterine muscles. Conclusion and Implications: These data suggest a role for both endo-cannabinoids and phytocannabinoids in the control of uterine smoothmuscle contractions. Whilst the precise mechanism through whichthese inhibitory effects are mediated is currently unclear, it is likely toinvolve CB1receptors.