Antinociceptive effect of Nidularium procerum: a Bromeliaceae from the Brazilian coastal rain forest

Nidularium procerum, a common plant of the Brazilian flora, has not yet been studied for its pharmacological properties. We report here that extracts of N. procerum show both analgesic and anti-inflammatory properties. Oral (p.o.) or intraperitoneal (i.p.) administration of an aqueous crude extract from leaves of N. procerum (LAE) inhibited the writhing reaction induced by acetic acid (ED50 value=0.2 mg/kg body weight, i.p.) in a dose-dependent manner. This analgesic property was confirmed in rats using two different models of bradykinin-induced hyperalgesia; there was 75% inhibition of pain in the modified Hargreaves assay, and 100% inhibition in the classical Hargreaves assay. This potent analgesic effect was not blocked by naloxone, nor was it observed in the hot plate model, indicating that the analgesic effect is not associated with the activation of opioid receptors in the central nervous system. By contrast, we found that LAE (0.02 μg/ml) selectively inhibited prostaglandin E2 production by cyclooxygenase (COX)-2, but not COX-1, which is a plausible mechanism for the analgesic effect. A crude methanol extract from the leaves also showed similar analgesic activity. An identical extract from the roots of N. procerum did not, however, block acetic acid-induced writhes, indicating that the analgesic compounds are concentrated in the leaves. Finally, we found that LAE inhibited an inflammatory reaction induced by lipopolysaccharide in the pleural cavity of mice.