CONICET | Buscador de Institutos y Recursos Humanos

Anandamide (AEA), an endocannabinoid, binds to cannabinoid receptor 1 (CB1) and 2 (CB2), besides vanilloid receptors. High concentrations of AEA are toxic for implantation and embryo development, suggesting a relevant role for AEA during early pregnancy. Nitric oxide (NO) is synthetized by nitric oxide synthase (NOS) and modulates vessel formation at the implantation sites. We have previously observed that uterine NOS activity is inversely correlated with AEA production at the implantation period. Thus, the aim of this study was to investigate if AEA modulated uterine NOS activity during implantation. Wistar rats were sacrificed in days 4, 5 and 6 of gestation. Implantation occurs in the afternoon of day 5. Pseudopregnancy (psp), a model in which the blastocyst is absent, was induced by i.p. administration of PMSG to prepuber rats. Rats on day 5 of psp were sacrificed. NOS activity and CBs expression and localization were determined in the uterus. AEA (1 nM) inhibited NOS activity in day 5 of psp (p<0.001) and this effect was completely reverted by the pre-incubation with SR144528 (0.1 nM), a selective CB2 antagonist. SR141716A (0.1 nM), a selective CB1 antagonist, had no effect. However, AEA (1 nM) increased NOS activity in the uterus from day 5 pregnant rats (8.0±0.3 vs 11.1±0.6 fmoles L-[14C]-citruline/mg ww/15 min, p<0.001) and this stimulatory effect was also reversed by SR144528. Finally, both CB1 and CB2 were expressed in the rat uterus in days 4, 5 and 6 of gestation (western blot and real time PCR) and they were localized to the luminal endometrium. Our results suggest that in the day of implantation, AEA effect on uterine NOS activity depends on the presence of the blastocyst. Besides the expression of CB1, we described for the first time the presence of CB2 in the rat uterus during the peri-implantation period.