ACTA ENDOCRINOLOGICA (BUC)

Background. Our study outlines the implication of melatonin in organisms' pain regulatory mechanisms. The literature describes epiphysis opioidergic fibers with µ and d opioid receptors and also pleads for an analgesic dose-dependent effect of melatonin. We analyzed the biologic variability of the analgesic effect of the pineal hormone, based on the psychoneuroendocrine behavior type. In our previous studies we investigated the dinamics of melatonin's analgesic effect within the following psychoneuroendocrine behavioral types: the adrenergic type (hipersensitive to pain), the opioid type (pain hyporeactive) and the intermediate, equilibrated typology (N type). Objectives. Our present research focused on the antinociceptive pharmacologic psychoneuroendocrine variability in the case of co-administration of melatonin (50mg/kgbw, i.p.) with ondansetron (4 mg/kgbw, i.p.), petidine (4mg/kgbw, i.p.) and tramadol (4mg/kgbw, i.p.). Subjects and Methods. Experiments were performed in vivo, using Albino Swiss male mice. Pain sensitivity was assessed using the classical pharmacologic test hot-plate (60°C). Conclusions. Our results showed an amplification of the analgesic effect when petidine was co-administered with melatonin, with best results for the A type of behavior (p<0.02), as follows: 63.41% (melatonin + petidine co-administration) > 54.54% (melatonin + tramadol coadministration) ≈ 52% (melatonin). We also noticed an antagonism between ondansetron and the pineal biomolecule