Inotropic effects of extracts of Psidium guajava L. (guava) leaves on the guinea pig atrium

Abstract

Many pharmacological effects have been ascribed to extracts of Psidium guajava L. (guava) leaves. However, in spite of its widespread use in Brazilian folk medicine and a reasonable number of scientific reports about it, we could not find any study dealing with its action on the mammalian myocardium. In the present study, by measuring isometric force, we observed that the crude extract of P. guajava (water-alcohol extract obtained by macerating dry leaves) depresses the guinea pig atrial contractility in a concentration-dependent fashion (N = 8 hearts, 15 trials). The compound with cardiac activity was concentrated by extraction in a Soxhlet apparatus using 17 M glacial acetic acid after removing the less polar fractions (hexane, chloroform, acetone, ethanol and methanol), suggesting that this compound is a highly polar substance. In the isolated guinea pig left atrium the acetic acid fraction (10-800 mg/l) of P. guajava 1) reversibly decreased myocardial force in a concentration-dependent fashion (EC 50 = 0.07g/l, N = 5 hearts, 9 trials, P<0.05), 2) increased the atrial relaxation time measured at 20% of the force amplitude up to 35% (91 ± 15 to 123 ± 30 ms, N = 3 hearts, 6 trials, P<0.05), 3) abolished the positive staircase effect (Bowditch phenomenon) in a concentrationdependent fashion suggesting a decrease of the cellular inward calcium current (N = 4 hearts, 8 trials, P<0.05), and 4) its inotropic effect was abolished by cholinergic receptor blockade with 1.5 mM atropine sulfate, indicating a cholinergic involvement in the mechanism of action of the extract (N = 7 hearts, 15 trials, P<0.05). The acetic acid extract was 20 times more potent than crude extract (EC 50 = 1.4 g/l). The results showed that extracts from P. guajava leaves depress myocardial inotropism.

Effects of two medicinal plants Psidium guajava L. (Myrtaceae) and Diospyros mespiliformis L. (Ebenaceae) leaf extracts on rat skeletal muscle cells in primary culture

“…Our extracts could increase Mg 2+ in the cytoplasm and it is well known that this ion has powerful inhibitory effect on calcium release in skeletal muscle (Lamb, 2000). It was also reported that extracts of Psidium guajava could block the L-type calcium membrane channels (Conde-Garcia et al, 2003). Here, this pathway was not explored since depolarizing stimuli were not used, but direct activation of calcium release from SR.…”

Complete atrioventricular block on isolated guinea pig heart induced by an aqueous fraction obtained from Psidium guajava L. leaf

“…After Conde-Garcia et al (2003) reported that the crude extract from P. guajava leaf reduced the atrial contraction force, we decided to investigate if AqF also could act on the electrophysiological mechanisms of the mammalian heart. In underdeveloped countries, teas and infusions, prepared from P. guajava leaves, are used to control intestinal colics.…”

“…Despite that its effect on the mammalian heart remained unknown. Conde-Garcia et al (2003) reported that some extracts obtained from P. guajava leaf depress the myocardial contractility. To test if the extract are also able to interfere with the electrophysiological properties of the myocardium this work was designed.…”

“…Conde-Garcia et al (2003) showed that the leaf acetic extract is able to reduce the atrial contractile force in a concentration-dependent fashion. To better understand the properties of P. guajava extracts on mammalian heart, the present work aimed to study the electrocardiographic effects produced on the guinea pig heart by the aqueous fraction of the acetic extract.…”

Extract from leaf of Psidium guajava L depresses the guinea pig atrial contractility by interfering with potassium and calcium channels

“…However, very little information could be found dealing with P.guajava extracts on the mammalian myocardium. Conde-Garcia et al (2003) showed that its crude hydroalcohoolic extract depresses the guinea pig atrial contractility. This effect was completely abolished by atropine sulfate.…”