CONICET | Buscador de Institutos y Recursos Humanos

It is well known that ∆9-tetrahydrocannabinol (THC), the major active ingredient of marihuana can suppress reproductive function. All previous studies including ours indicated that the inhibitory effect of THC on the reproductive axis is exerted mainly at the hypothalamic level by inhibiting LHRH release with the consequent inhibition of LH secretion by the pituitary, thereby inhibiting gonadal function. To date two cannabinoid receptors have been cloned and characterized, the CB1 expressed mainly in the central nervous system and the CB2, mainly located on the peripheral tissues, especially in the immune system. We showed the presence of CB1 in the MBH of male rats, an area that contains the neurons involved in the synthesis and release of LHRH. The main endocannabinoid studied is anandamide (AEA). We showed that AEA (10-9M) decreased the N-methyl D-aspartic acid (NMDA)-stimulated LHRH release, and that AM251 (10-5M), a CB1 antagonist, totally reversed that effect, confirming the participation of the endocannabinoid system in LHRH release. We also demonstrated that AEA increased significantly the release of gamma-aminobutiric acid (GABA) from the MBH. Moreover, bicuculline (10-4M), a GABAergic antagonist, was capable of totally blocking the inhibitory effect of AEA on NMDA-stimulated LHRH release, confirming that GABA mediates the inhibition of LHRH induced by endocannabinoids. On the other hand, it is known that during the endotoxemia induced by lipopolysaccharide (LPS), the hypotalamic-gonadotropin axis is inhibited. LPS seems to activate similar mechanisms in the inhibitory pathway of LHRH to those exerted by cannabinoids, principally, by increasing GABAergic activity. Moreover, the intra peritoneal injection of LPS (5mg/Kg) as well as the icv injection of TNFa (100 ng/rat), a pro-inflammatory cytokine released rapidly after LPS administration, increased significantly the AEA synthesis measured ex vivo in MBH removed 3 h after the treatments. Furthermore, we found that TNFa (2.9x10-9M) increased the synthesis of AEA in MBH incubated in vitro. Secondly, we showed that TNFa reduced significantly the forskolin (an AC activator) stimulated LHRH release and that the CB1 antagonist, AM251 (10-5M), blocked this inhibition, supporting the hypothesis that TNFa inhibits LHRH release acting at least in part by activating the endocannabinoid system. In summary, our data demonstrate a key role for the endocannabinoid system in the response of the reproductive system to inflammatory signals. (BID 1728 OC-AR PICT 03-14264, PIP 6149 CONICET)