A main traditional use of European Leonurus cardiaca and East Asian Leonurus japonicus is in the treatment of neurological disorders such as anxiety, depression, nervousness, and as a sedative for insomnia. However, their mechanism of action is still under discussion. As anxiety and depressive disorders are increasingly being recognized as connected to dysfunctions of the gamma-aminobutyric acid system, the in vitro effects of standardized L. cardiaca and L japonicus extracts as well as five of their isolated constituents, namely, the labdane-type isoleosibirin, the novel iridoid 7R-chloro-6-desoxy-harpagide, the phenylethanoid lavandulifolioside, and the N-containing compounds stachydrine and leonurine, on this type of neuronal receptor were investigated for the first time. Extracts of L. cardiaca and L. japonicus, characterized by reversed-phase high-performance liquid chromatography determination, as well as their above named isolated, possible active constituents of different chemical nature were tested in several receptor binding assays at rat GABAA receptors using [(3)H]-SR95 531 and [(3)H]-Ro-15-1788 (flumazenil)/diazepam control. The L. cardiaca and L. japonicus extracts as well as leonurine inhibited the concentration-dependent binding of [(3)H]-SR95 531 to the gamma-aminobutyric acid site of the gamma-aminobutyric acid type A receptor with a high binding affinity: IC50s 21 µg/ml, 46 µg/ml, and 15 µg/ml, respectively. In contrast, binding to the benzodiazepine site of the rat gamma-aminobutyric acid type A receptor had a 15 to 30 times lower binding affinity than to the gamma-aminobutyric acid site. The presented experiments provide hints that the neurological mechanism of action of L. cardiaca and L. japonicus may essentially be based on their interaction to the gamma-aminobutyric acid site of the gamma-aminobutyric acid type A receptor, while the benzodiazepine site most probably does not contribute to this effect. In the case of L. japonicus, these effects can be at least partially explained by its leonurine constituent, whereas the active principle of L. cardiaca, which does not contain leonurine, is subject to further research as none of the other investigated individual constituents displayed significant activity in the applied test system.
Cardiac fibroblasts play an important role in adverse cardiac remodelling. As in many cardiac diseases connexin43 (Cx43) is altered, we wanted to elucidate whether fibroblasts may influence cardiac Cx43 expression. We used four different cell culture systems of neonatal rat cardiomyocytes (CM) and fibroblasts (FB): type 1, pure CM culture; type 2, co-culture of CM/FB; type 3, pure FB culture; type 4, Transwell® system: CM/FB co-cultured but separated by a microporous membrane. Stimulation of types 1-3 cell culture models with isoprenaline significantly enhanced Cx43-protein and Cx43-mRNA expression as well as phosphorylation of ERK and translocation of AP1 and CREB only in the CM cultures; whereas, the CM/FB co-cultures and the FB cultures did not respond to isoprenaline. Similarly, if CM and FB were separated by a microporous membrane (Transwell® system) the isoprenaline-induced increase in CM Cx43 was completely suppressed, suggesting the existence of a soluble factor responsible for the suppressant effect of FB. Angiotensin II determination in types 1 and 2 cell culture supernatants revealed that the CM/FB co-cultures exhibited a significant higher angiotensin II release than the CM cultures. Furthermore, we aimed to inhibit angiotensin II signal transduction pathway: blockade of AT1 receptors or PKC inhibition restored the responsiveness of CM/FB co-cultures to isoprenaline. Moreover, external addition of angiotensin II to CM cultures also resulted in suppression of isoprenaline-stimulated Cx43 expression in an AT1-receptor- and PKC-dependent manner. Thus, our study indicates that cardiac fibroblasts inhibit β-adrenoceptor-dependent Cx43 signalling in CM involving angiotensin II.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.