ABSTRACT
The present study was designed to further evaluate a possible spasmolytic activity of synthetic lapachol derivatives, norlapachol, alpha-norlapachone, beta-norlapachone and hydro-hydroxy-norlapachol (HH-norlapachol), on guinea-pig ileum. In guinea-pig ileum, except for norlapachol, all naphthoquinones inhibited the phasic contractions induced by carbachol or histamine. Even when the ileum was pre-contracted with KCl, carbachol or histamine, all naphthoquinones induced relaxation, suggesting that these naphthoquinones could be acting on the voltage-gated calcium channels (Ca(V)). As the tonic component this contraction is maintained mainly by the opening of the Ca(V), we hypothesized that these naphthoquinones might be acting on these channels. This hypothesis was confirmed by the observation that norlapachol (pD'2 = 4.99), alpha-norlapachone (pD'2 = 4.49), beta-norlapachone (pD'2 = 6.33), and HH-norlapachol (pD'2 = 4.53) antagonized the contractions induced by CaCl2 in depolarizing medium nominally without Ca2+. As beta-norlapachone was the most potent we decided to continue the study of its action mechanism. The fact that this naphthoquinone has inhibited the tonic contractions induced by S-(-)-Bay K8644 [EC50 = (1.6 +/- 0.30) x 10(-5) M] suggests that the Ca2+ channel involved belongs to the type L (Ca(V)1.2). In addition, in the functional level, the spasmolytic effect of beta-norlapachone does not involve participation of free radicals, since its curve of relaxation was unchanged in the presence of glutathione, an antioxidant agent.
Subject(s)
Ileum/physiology , Muscle Relaxation/physiology , Naphthoquinones/pharmacology , 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/pharmacology , Animals , Calcium Channel Agonists/pharmacology , Guinea Pigs , Histamine/pharmacology , Ileum/drug effects , Muscle Contraction/drug effects , Muscle Contraction/physiology , Muscle Relaxation/drug effects , Naphthoquinones/isolation & purification , Potassium Chloride/pharmacology , Tabebuia/chemistryABSTRACT
Xylopia langsdorfiana A. St.-Hil. &Tul. (Annonaceae) is popularly known in the northeast of Brazil as 'pimenteira da terra', and an essential oil (XL-OE) was extracted from its leaves. Since Xylopia species are cited in folk medicine and diterpenes from X. langsdorfiana have spasmolytic activity, this study aimed to investigate a possible spasmolytic action of XL-OE on smooth muscle models. XL-OE (243 and 729 µg/mL) showed low pharmacologic efficacy on guinea pig trachea and rat aorta and uterus. However, in guinea pig ileum, XL-OE (27-729 µg/mL) inhibited carbachol or histamine-induced phasic contractions (1 µM) in a significant and concentration-dependent manner. In addition, XL-OE (81 µg/mL) reduced fluorescence intensity in ileal myocytes stimulated by histamine, indicating a decrease in cytosolic calcium concentration, which could explain the spasmolytic activity. Thus, XL-OE proved to be a promising natural product to be used in gastrointestinal diseases acting by modulating the cytosolic calcium concentration.