N-(4-Methoxy-2-nitrophenyl)hexadecanamide, a palmitoylethanolamide analogue, reduces formalin-induced nociception

Aims: To investigate the local antinociceptive effect as well as the possible mechanisms of action of a novel analogue of palmitoylethanolamide (PEA) N-(4-methoxy-2-nitrophenyl)hexadecanamide (HD) in the rat formalin test. Main methods: The formalin test was used to assess the antinociceptive activity of HD in vivo. The hydrolysis of anandamide catalyzed by fatty acid amide hydrolase (FAAH) was used to determine the action of HD on FAAH activity in vitro. Key findings: Local peripheral ipisilateral, but not contralateral, administration of HD (10-100 μg/paw) produced a dose-dependent antinociceptive effect in rats. The CB₁ and CB₂ receptor antagonists AM281 (0.3-30 μg/paw) and SR144528 (0.3-30 μg/paw), respectively, reduced the antinociceptive effect of HD (100 μg/paw). In addition, methiothepin (0.03-0.3 μg/paw) and naloxone (5-50 μg/paw) significantly reduced HD-induced antinociception (100 μg/paw). In vitro, HD reduced only to a minor extent the hydrolysis of anandamide catalyzed by FAAH. Significance: HD local administration produces antinociception that probably results from an indirect activation of peripheral CB₁ and CB₂ cannabinoid receptors. Data suggest that 5-HT₁ and opioid receptors also participate in the antinociceptive effect of this compound. HD may have potential as analgesic drug.