Akademik Veri Yönetim Sistemi
Molecular and Cellular Biochemistry, cilt.335, sa.1-2, ss.59-66, 2010 (SCI-Expanded)
Thyroid hormone deficiency has been reported to decrease expression and function of both β1- and β2-adrenoceptor in different tissues including heart. The purpose of this study was to examine the possible contribution of β3-adrenoceptors to cardiac dysfunction in hypothyroidism. In addition, effect of this pathology on β1- and β2-adrenoceptor was investigated. Hypothyroidism was induced by adding methimazole (300 mg/l) to drinking water of rats for 8 weeks. Cardiac hemodynamic parameters were measured in anesthetised rats in vivo. Responses to β-adrenoceptor agonists were examined in rat papillary muscle in vitro. We also studied the effect of hypotyroidism on mRNA expression of β-adrenoceptors, Giα, GRK, and eNOS in rat heart. All of the hemodynamic parameters (systolic, diastolic and mean arterial pressure, left ventricular pressure, heart rate, +dp/dt, and -dp/dt) were significantly reduced by the methimazole treatment. The negative inotropic effect elicited by BRL 37344 (a β3-adrenoceptor preferential agonist) and positive inotropic effects produced by isoprenaline and noradrenaline, respectively, were significantly decreased in papillary muscle of hypothyroid rats as compared to those of controls. On the other hand, hypothyroidism resulted in increased cardiac β2- and β3-adrenoceptor, Giα2, Giα3, GRK3, and eNOS mRNA expressions. However, β1-adrenoceptor and GRK2 mRNA expressions were not changed significantly in this pathology. These results show that mRNA expression of β3-adrenoceptors as well as the signalling pathway components mediated through β3-adrenoceptors are significantly increased in hypothyroid rat heart. Since we could not correlate these alternates with the decreased negative inotropic response mediated by this receptor subtype, it is not clear whether these changes are important for hypothyroid induced reduction in cardiac function. © 2009 Springer Science+Business Media, LLC.