“Role of the Phosphodiesterase-5 Inhibitor (Tadalafil) In Morphine Induced Analgesia in Rats” Summary

The current study addressed two important concerns, one pertinent to the impact of PDE-5 inhibitor (tadalafil) on morphine-induced analgesia and the second relevant to its influence on morphine-induced oxidative stress in two different pain models, the the tail-flick test (representing an acute thermal phasic pain model ) and the formalin test (representing an inflammatory tonic pain model ). This study was performed in adult male albino rats treated with morphine in the absence or presence of tadalafil, a PDE-5 inhibitor, L-NAME, a non selective nitric oxide synthase inhibitor and methylene blue, a guanylyl cyclase inhibitor, to investigate the effect of these interventions on morphine-induced analgesia and oxidative stress. The former was evaluated through measurement of tail-flick latencies (represented as MPE) and hind paw flinches (represented as AUC) in both tail flick test and formalin test, respectively. The latter was detected through assessment of various biochemical parameters in the rat liver homogenates including GSH, total GPX activity and MDA.