Context: Agastache mexicana ssp. mexicana (Kunth) Lint & Epling (Lamiaceae), popularly known as ‘toronjil morado’, is used in Mexican traditional medicine for the treatment of several diseases such as hypertension, anxiety and respiratory disorders. Objective: This study investigates the relaxant action mechanism of A. mexicana ssp. mexicana essential oil (AMEO) in guinea-pig isolated trachea model. Materials and method: AMEO was analyzed by GC/MS. The relaxant effect of AMEO (5–50 μg/mL) was tested in guinea-pig trachea pre-contracted with carbachol (3 × 10 ^{− 6} M) or histamine (3 × 10 ^{− 5} M) in the presence or absence of glibenclamide (10 ^{− 5} M), propranolol (3 × 10 ^{− 6} M) or 2′,5′-dideoxyadenosine (10 ^{− 5} M). The antagonist effect of AMEO (10–300 μg/mL) against contractions elicited by carbachol (10 ^{− 15}–10 ^{− 3} M), histamine (10 ^{− 15}–10 ^{− 3} M) or calcium (10–300 μg/mL) was evaluated. Results: Essential oil composition was estragole, d-limonene and linalyl anthranilate. AMEO relaxed the carbachol (EC₅₀=18.25 ± 1.03 μg/mL) and histamine (EC₅₀=13.3 ± 1.02 μg/mL)-induced contractions. The relaxant effect of AMEO was not modified by the presence of propranolol, glibenclamide or 2′,5′-dideoxyadenosine, suggesting that effect of AMEO is not related to β₂-adrenergic receptors, ATP-sensitive potassium channels or adenylate cyclase activation. AMEO was more potent to antagonize histamine (pA₂′ = −1.507 ± 0.122) than carbachol (pA₂′ = −2.180 ± 0.357). Also, AMEO antagonized the calcium chloride-induced contractions. Conclusion: The results suggest that relaxant effect of AMEO might be due to blockade of calcium influx in guinea-pig trachea smooth muscle. It is possible that estragole and d-limonene could contribute majority in the relaxant effect of AMEO.

Despite the availability of many anti-pain drugs, in the form of NSAIDs, steroids, gabapentinoids, opioids, and antidepressants, in this study we address the natural compounds belonging to the group of Mexican medicinal plants or “Mexican folk medicine”, used for pain management in Mexico. Our interest in this subject is due to the growing idea that “natural is harmless” and to the large number of side effects exhibited in pharmacotherapy. The objective of this review was to document the scientific evidence about Mexican medicinal plants and their derivatives used for inflammatory and neuropathic pain treatment, as well as the mechanisms of action implicated in their antinociceptive effects, their possible adverse effects, and the main pharmacological aspects of each plant or compound. Our data review suggested that most studies on Mexican medicinal plants have used inflammatory experimental models for testing. The anti-pain properties exerted by medicinal plants lack adverse effects, and their toxicological assays report that they are safe to consume; therefore, more studies should be performed on preclinical neuropathic pain models. Moreover, there is no convincing evidence about the possible mechanisms of action involved in the anti-pain properties exerted by Mexican plants. Therefore, the isolation and pharmacological characterization of these plant derivatives’ compounds will be important in the design of future preclinical studies.