Erythroxylum pungens elicits vasorelaxation by reducing intracellular calcium concentration in vascular smooth muscle cells of rats

The cardiovascular effects elicited by the ethanolic extract obtained from the roots of Erythroxylum pungens O.E. Schulz, Erythroxylaceae (EEEP) and the vasorelaxant effect induced by its main tropane alkaloid (pungencine) were investigated. In normotensive rats, administration of EEEP (1, 10, 30 and 60 mg/kg i.v., randomly) produced dose-dependent hypotension (-2±1, -7±0.5 -17.6±1, -24±1 ∆ mmHg, n=5) followed by tachycardia (3±0.5, 7±2, 7.1±1, 10±5 ∆ bpm, n=5). In intact phenylephrine (Phe, 10 μM)-pre-contracted rings, EEEP (0.01-500 μg/mL) induced concentrationdependent vasorelaxation (EC50 13.7±5.5 μg/mL, Maximal Response= 92±2.6%), and this effect was unchanged after the removal of the vascular endothelium (EC50 27.2±4.7 μg/ml, Maximal Response= 88.3±3.3 %). In KCl (80 mM)-pre-contracted-endotheliumdenuded rings, EEEP elicited concentration-dependent relaxation (EC50= 128.2±11.2 μg/mL, Maximal Response 76.8±3.4%). Vasorelaxation has also been achieved with tonic contractions evoked by the L-type Ca2+ channel agonist Bay K 8644 (EC50 80.2±9.1 μg/mL, Maximal Response 86.3±8.3%). In addition, in a depolarizing medium, EEEP inhibited CaCl2 (30-500 μg/mL) induced contractions and caused a concentrationdependent rightward shift of the relaxation curves. Lastly, the tropane alkaloid pungencine caused vasorelaxation in mesenteric arteries resembling to the EEEP responses. These results suggests that EEEP induces hypotension and vasorelaxation, at least in part, due to the reduction in [Ca2+]i in vascular smooth muscle cells.