Antihyperalgesic activity of an extract and compounds from Anoda cristata

Anoda cristata (Malvaceae) is used as food and to treat stomach complaints, fever, cough, wounds and diabetes. In a previous work, the antidiabetic action of a free mucilage aqueous extract (FM-AE) and major compounds [acacetin (1) and diosmetin (2)] from the plant was reported. This work was undertaken to establish the potential antihyperalgesic action of A. cristata using the formalin test in hyperglycemic (NA/STZ: 50/130 mg/kg, i.p.) mice. In all cases the treatments were administered subcutaneously in the dorsal surface of the right hind paw. FMAE (10 – 100 µg/paw), 1 (1 – 7.5 µg/paw) and 2 (0.1 – 6 µg/paw), induced significant decrease in licking time. In order to determine the mode of action of 1 and 2, the animals were pretreated with naloxone (3 µg/paw), flumazenil (6 µg/paw), ketanserin (3 µg/paw), L-NAME (150 µg/paw), ODQ (75 µg/paw) or glibenclamide (3 µg/paw). The effect of 1 was abolished with naloxone and flumazenil, revealing its opioid and GABA mechanisms of action. However, pretreatment with ketanserin was the only one that antagonized the effect of 2, consistent a serotonergic pathway mediating its pharmacological action. The antihyperalgesic effect of FMAE, 1 and 2 could be of benefit in diabetic patients with neuropathic complications.