Dual Effect of Anandamide on Rat Placenta Nitric Oxide Synthesis

Anandamide (AEA) has been reported to have pleiotropic effects on reproduction, but the mechanism by which it exerts these effects is unclear. The aim of this study is to characterize rat placental endocannabinoid system and to analyze the possible functional role of AEA in the regulation of NO levels in rat placenta during pregnancy. We found that cannabinoids receptors (CB1 and CB2), FAAH and TRPV1 were expressed in chorio-allantoic placenta. NOS activity peaked at day 13 and decreased with progression of pregnancy. Both exogenous and endogenous AEA significantly decreased NOS activity. Although pre-incubation with AM251 (CB1 antagonist) or AM630 (CB2 antagonist) had no effect, co-incubation with both antagonists induced NOS activity. Furthermore, pre-incubation with exogenous AEA and both antagonists resulted in the induction of placental NOS activity and this effect was reverted with capsazepine (selective TRPV1 antagonist). Additionally, the enhanced NO synthesis caused by capsaicin was abrogated by co-treatment with capsazepine, illustrating that NOS activity could be modulated by TRPV1. Finally, the inhibition of TRPV1 receptor by capsazepine caused a significant fall in NOS activity. These data support the concept that AEA modulates NO levels by two independent pathways: (1) diminishing the NOS activity via CBs; and (2) stimulating NO synthesis via TRPV1. We hypothesized that AEA have an important implication in the normal function of placental tissues.