Effect of amiodarone and dronedarone administration in rats on thyroid hormone-dependent gene expression in different cardiac components.

OBJECTIVE: In view of their different actions on thyroid hormone receptor (TR) isoforms we set out to investigate whether amiodarone (AM) and dronedarone (Dron) have different and/or component-specific effects on cardiac gene expression. DESIGN: Rats were treated with AM or Dron and the expression of TRalpha 1, TRalpha 2, TRbeta 1 and several tri-iodothyronine (T3)-regulated genes was studied in different parts of the heart, namely the right atrium (RA), left ventricular wall (LVW) and apex. METHODS: Rats were treated for 14 days with 100 mg/kg body weight AM or Dron. The expression of TRalpha 1, TRalpha 2, TRbeta 1 and T3-regulated genes was studied using real-time PCR and non-radioactive in situ hybridisation. RESULTS: AM and Dron affected TR expression in the RA similarly by decreasing TRalpha 1 and beta 1 expression by about 50%. In the LVW, AM and Dron decreased TRbeta 1 and, interestingly, AM increased TRalpha 1. In the apex, AM also increased TRalpha 2. The changes seen in T3-dependent gene expression are reminiscent of foetal reprogramming. CONCLUSION: Taken together, our results indicate that AM and Dron have similar effects on the expression of TR isoforms in the RA, which could partly contribute to their ability to decrease heart rate. On the other hand, the more profound effect of AM appears on TR- and T3-dependent gene expression in the left ventricle suggests foetal reprogramming.

Expression pattern and ontogenesis of thyroid hormone receptor isoforms in the mouse heart.

Nuclear thyroid hormone (T3) receptors (TR) play a critical role in mediating the effects of T3 on development, differentiation and normal physiology of many organs. The heart is a major target organ of T3, and recent studies in knockout mice demonstrated distinct effects of the different TR isoforms on cardiac function, but the specific actions of TR isoforms and their specific localization in the heart remain unclear. We therefore studied the expression of TRalpha1, TRalpha2 and TRbeta1 isoforms in the mouse heart at different stages of development, using monoclonal antibodies against TRalpha1, TRalpha2 and TRbeta1. In order to identify distinct components of the embryonic heart, in situ hybridization for cardiac-specific markers was used with the expression pattern of sarcoplasmic reticulum calcium-ATPase 2a as a marker of myocardial structures, while the pattern of expression of connexin40 was used to indicate the developing chamber myocardium and peripheral ventricular conduction system. Here we show that in the ventricles of the adult heart the TRbeta1 isoform is confined to the cells that form the peripheral ventricular conduction system. TRalpha1, on the other hand, is present in working myocardium as well as in the peripheral ventricular conduction system. In the atria and in the proximal conduction system (sinoatrial node, atrio-ventricular node), TRalpha1 and TRbeta1 isoforms are co-expressed. We also found the heterogeneous expression of the TRalpha1, TRalpha2 and TRbeta1 isoforms in the developing mouse heart, which, in the case of the TRbeta1 isoform, gradually revealed a dynamic expression pattern. It was present in all cardiomyocytes at the early stages of cardiogenesis, but from embryonic day 11.5 and into adulthood, TRbeta1 demonstrated a gradual confinement to the peripheral ventricular conduction system (PVCS), suggesting a specific role of this isoform in the formation of PVCS. Detailed knowledge of the distribution of TRalpha1 and TRbeta1 in the heart is of importance for understanding not only their mechanism of action in the heart but also the design and (clinical) use of TR isoform-specific agonists and antagonists.

A post-ischaemic single administration of galanthamine, a cholinesterase inhibitor, improves learning ability in rats.

Transient forebrain ischaemia is widely observed in clinical practice. We have examined the effect of a single administration of the cholinesterase inhibitor galanthamine (2mg kg(-1) i.p.) 25 min after reperfusion in male Sprague-Dawley rats (180 +/- 20 g) after a 20-min common carotid artery occlusion. Twenty-four-hours post-ischaemia there was no difference in motor co-ordination or muscle tonus of the rats treated with or without galanthamine as assessed by the rota-rod test. Learning ability was examined using the shuttle-box test, evaluating the latency time and the number of errors for six days in succession. The performance of the ischaemic saline-injected rats was significantly impaired on days 4, 5, 6 (latency time) compared with the non-ischaemic rats and with the ischaemic animals administered galanthamine (P < 0.05). Similar results were obtained when counting the number of errors (failure to cross the cage during conditioned or unconditioned stimulus). The monitoring of body temperature during the first 12-h post-ischaemia did not show any significant difference between the groups. The data showed a beneficial effect of galanthamine on the recovery of learning ability when administered once only post-ischaemia. This suggests a direct effect on the early pathologic mechanisms of CNS damage. Cholinesterase inhibitors may prove useful in the early clinical treatment of ischaemic conditions.

Estradiol inhibits astrocytic GFAP expression in an animal model of neuroinflammation.

There are many animal models for studying different aspects of neurodegeneration. Lipopolysaccharide (LPS) injected in rats intracerebroventricularly induces neuroinflammation quite similar to the inflammatory component of chronic neurodegenerative conditions such as Alzheimer's disease. We used this model to examine the effect of estradiol on neuroinflammation. LPS or pyrogen-free saline were injected intracerebroventricularly (i.c.v.) into the lateral ventricle of male Wistar rats and estradiol was administered (200 micrograms/kg s.c.) 48 h before or 24 h after LPS injection. LPS-induced body weight loss was partially postponed by the treatment, especially in the rats pretreated with estradiol. When analyzing GFAP glial cell morphology in the CA3c area of the hippocampus and corpus callosum, as well as the number of astroglial cells in CA3c and CA1, GFAP expression was found to be reduced. This was true especially in the animals pretreated with estradiol and to a much lesser extent in the posttreated ones. The data support the possible existence of a neuroimmunomodulatory effect of estradiol administration in neurodegenerative conditions, which influences the inflammatory component.