CANNABINOID INDUCED CHANGES IN RAT UTERINE CONTRACTILITY

Abstract

Background: Endocannabinoids have been demonstrated in many mammalian tissues. It was reported that exposure to exocannabinoids (e.g. marijuana) is associated with adverse pregnancy outcomes. Objective: The present study was designed to demonstrate the effect of anandamide on spontaneous contraction of pregnant and non pregnant rat uterus and the possible involvement of cannabinoid CB1 receptors, Nitric Oxide(NO), and small conductance Ca+2 activated K+ channels in anandamide induced effect. Design: The present study was carried out on a total number of 30 adult albino rats (24 females and 6 males). The animals were obtained from the laboratory animals' farm unit Faculty of Veterinary Medicine, Zagazig University, with an average weight, 180-200 grams. The male rats were used for induction of pregnancy. The first day of pregnancy was determined by the presence spermatozoa in the vaginal smear examined microscopically. The female rats were divided into four equal groups (6 for each). Three groups (non pregnant, day 10 and day 19 of gestation) were used to study the effects of anandamide (10-6, 10-5 and 10-4 M/ml organ bath fluid) on spontaneous contractile activity of isolated uterine strips. The fourth group (day 10 of gestation) was used to study the possible mechanisms of action of anandamide using CB (1) receptor antagonist (AM251, 10-6 M/L), NG-nitro-L-arginine methyl ester (L- NAME, 3 x 10-5 M/L), and small conductance Ca+2 activated K+ channels blocker (Apamin, 10-8 M/L). Results: The present study showed that anandamide exerted a significant dose dependant reduction in frequency and amplitude of spontaneous contraction of uterine strips isolated from both pregnant and non pregnant rats. The present study also revealed that the utero-relaxant effect of anandamide was significantly more potent in uterine strips isolated from pregnant rats on day 10 of gestation than that in both non pregnant rats and pregnant rats on day 19 of gestation. After incubation of uterine strips isolated from pregnant rats on day 10 of gestation with the specific CB1 receptor antagonist AM251, the utero-relaxant effect of anandamide was almost completely abolished. This finding indicates that CB1 receptors are present in the rat uterus and may be the main receptor subtype involved in endocannabinoid-induced uterine relaxation. It was also found that pretreatment of uterine strips with NO synthase inhibitor (L-NAME) and small conductance-Ca+2 activated K+ channel blocker (Apamin) significantly decreased the anandamide induced utero-relaxant effect. Conclusion: In conclusion, anandamide exerts a potent relaxant effect in vitro on uterine strips isolated from pregnant and non pregnant rat uterus. This relaxant effect is higher in mid-gestation and this may help uterine quiescence during pregnancy, and then diminishes in late pregnancy which may allow effective uterine contraction during labor. In addition, the direct relaxant effect of anandamide is mediated through binding with CB1 receptors. Moreover, activation of nitric oxide generation and opening of small conductance Ca++ activated K+ channels play a role in this anadamide induced utero-relaxant effect. This study highlights the possibility of a physiologic role for endogenous cannabinoids during human pregnancy and parturition and supports the view that exogenous cannabis use during pregnancy may have adverse effects on pregnancy and delivery. Key word: Endocannabinoids, uterine contractility and pregnancy.