The central hypotensive effect induced by methionin-enkephalin involves a serotonergic pathway.

Both endogenous opiate peptides and serotonin are known to be involved in blood pressure control. In this work we present results obtained in anaesthetized normotensive rats in which we studied the possible interaction between the central blood pressure effects induced by methionin (met)-enkephalin and serotonergic pathways. Met-enkephalin administered intracerebroventricularly produced a dose-dependent hypotensive action that was prevented by pretreating the animals with naloxone (opioid antagonist), or with methiothepin (serotonergic S1 and S2 receptor antagonist) or 5,7-dihydroxytryptamine (a serotonergic neurotoxin). In contrast, ritanserin, a serotonergic S2 receptor antagonist, failed to alter the hypotensive action of met-enkephalin. These data suggest that the central activation of opiate receptors induces a hypotensive action in which a serotonergic pathway is required. In this case the serotonergic receptor involved seems to belong to the S1 subtype.