Negative inotropic and chronotropic effects on the guinea pig atrium of extracts obtained from Averrhoa carambola L. leaves

Abstract

It has been reported that star fruit can lead to a fatal outcome in uremic patients. The intoxication syndrome consists of hiccups, mental confusion, dizziness, and vomiting. On the other hand, folk medicine uses teas and infusions of carambola leaves to treat headache, vomiting, cough, insomnia, and diabetes. This motivated us to determine if Averrhoa carambola can act on the contractility and automaticity of the guinea pig heart. We measured the atrial isometric force in stimulated left atria and determined the chronotropic changes in spontaneously beating right atria. The carambola leaf extracts (1.5 mg/ml) abolished the contractile force in a concentration-dependent manner. Among the crude, methanolic, ethanolic, aqueous, and acetic extracts, the aqueous one was the most potent (EC 50 = 520 ± 94 µg/ml; flavonoids and tannins are the main constituents; Na + and K + contents in 1.0 mg/ ml of aqueous extract were 0.12 ± 0.016 and 1.19 ± 0.15 mM, respectively). The aqueous extract abolished the positive Bowditch staircase phenomenon and reduced the inotropic response to CaCl 2 (0.17-8.22 mM), events that are dependent on the cellular Ca 2+ inward current. The adrenergic, muscarinic or opioid membrane receptors do not seem to participate in the mechanism of action of the cardioactive substance(s). In spontaneously beating atria, the aqueous extract promoted a negative chronotropic effect that was antagonized by 0.1 µM isoproterenol bitartrate. With this agonist, the EC 50 of the aqueous extract increased from 133 ± 58 to 650 ± 100 µg/ml. These data regarding the effect of A. carambola on guinea pig atrial contractility and automaticity indicate an L-type Ca 2+ channel blockade.

Inhibition of Human Liver Cytochrome P450 by Star Fruit Juice

“…Star fruit, largely planted in Southeast Asia and Brazil, is a popular fruit around the world (14). It is recommended in folk medicine as a diuretic, expectorant, and cough suppressant (21)(22)(23). For Brazilians, it is common to drink 300 to 500 mL of star fruit juice in a single day (24,25).…”

Aqueous leaf extract of Averrhoa carambola L. (Oxalidaceae) reduces both the inotropic effect of BAY K 8644 on the guinea pig atrium and the calcium current on GH3cells

“…When acting on the natural right atrial pacemaker, this extract promoted a signifi cant bradicardia (Vasconcelos et al, 2005). In guinea pig isolated heart, it was observed that AqEx induced different degrees of atrioventricular block (Vasconcelos et al, 2006).…”

“…These clinical manifestations have only disappeared after administrating propofol or when the patients were submitted to hemodialysis (Tsai et al, 2005;Wang et al, 2006). Vasconcelos et al (2005) reported that the AqEx of A. carambola leaves exerts a negative inotropic and chronotropic effects on the guinea pig atria. Furthermore, Vasconcelos et al (2006) showed that it decreased the conduction velocity of the atrial impulse and increased the elapsed time to conduct the myocardial impulse from the right atrium to the His bundle.…”

A Comprehensive Review of An Important Medicinal Plant – Averrhoa carambola L.

“…[26] Aqueous extract of the leaves act as an agent that strongly depresses the heart rate and the myocardial contractile force. [27] The active compound has not been identified, but the action on L-type Ca 2+ channels is important to explain the mechanism of action of this plant on the mammalian atrial myocardium. [27] In India, the ripe carambola fruit or its juice may be taken to counteract fever.…”

“…[27] The active compound has not been identified, but the action on L-type Ca 2+ channels is important to explain the mechanism of action of this plant on the mammalian atrial myocardium. [27] In India, the ripe carambola fruit or its juice may be taken to counteract fever. [6] A salve made of the fruit is employed to relieve eye afflictions.…”