Total phenolic and flavonoid contents and antihypertensive effect of the crude extract and fractions of Calamintha vulgaris

Abstract

Background: Calamintha vulgaris L., has been used medicinally in the management hypertension.

Purpose: To investigate the antihypertensive mechanisms of extract of C. vulgaris L., in Sprague-Dawley (SD) rat.

Study design: Total phenol and total flavonoid contents were determined in the crude extract through HPLC. In vivo and in vitro pharmacological approaches were utilized to test the crude extract and fractions of C. vulgaris in Sprague-Dawley (SD) rats. The effect on mean arterial pressure (MAP) was compared in normotensive and high salt-induced hypertensive rats.

Methods: Crude extract and nHexane, chloroform, ethylacetate and aqueous fractions of C. vulgaris were tested. In vitro experiments were carried out in isolated rat and rabbit aortae, to probe vascular mechanism(s). Extract was also evaluated for acute toxicity study in mice.

Results: Crude extract and fractions of C. vulgaris induced a fall in MAP in normotensive and high salt-induced hypertensive rats at different doses. The effect was more significant in the hypertensive rats (Max. fall, 38.67 ± 2.17 vs 44.16 ± 4.67 mmHg). Among the fractions, chloroform was more effective (Max. fall, 53.20 ± 1.23 mmHg) and aqueous the least (Max. fall, 38.66 ± 1.12 mmHg). Normotensive rats pretreated with atropine (2 mg/kg) or _L-NAME (100 µg/kg) ablated fall in MAP to the extract and fractions. In isolated rat aorta, extract induced endothelium-dependent vasodilatory effect, which was ablated with atropine (1 µM), _L-NAME (10 µM), atropine + _L-NAME, TEA (10 µM) pretreatment and denudation of aorta. Indomethacin (10 µM) pretreatment ablated vasodilatation at lower concentrations and unmasked a vasoconstrictor effect, followed by relaxation at higher concentrations. Extract and fractions inhibited high K⁺-precontractions and rightward shifted Ca⁺² concentration response curves, similar to verapamil. Total phenolic and flavonoid contents were found 39.41 ± 0.18 (mg of GAE/g) and 12.03 ± 0.23 (mg of QUE/g), respectively. HPLC analysis showed the presence of quercetin and rutin CONCLUSION: Results obtained indicate that the antihypertensive effect of C. vulgaris is the outcome of vasodilation, which is mediated through combination of muscarinic receptor-linked NO, activation of TEA-sensitive K⁺ channels, prostacyclin and Ca⁺² antagonism.

Keywords: Antihypertensive; Ca(+2) antagonist; Calamintha vulgaris; Endothelium-dependent and –independent; HPLC analysis; Muscarinic receptors-linked NO; Prostacyclin (PGI(2)).