Effect of metoprolol on activity of β-adrenoceptor coupled to guanine nucleotide binding regulatory proteins in adriamycin-induced cardiotoxicity

Abstract

Prevention of cardiotoxicity without interfering with the therapeutic efficacy of adriamycin is a very crucial question. We have investigated the activity of beta-adrenoceptor coupled to guanine nucleotide binding regulatory proteins (G-proteins) and Ca(2+)-ATPase activity in experimental adriamycin-induced cardiotoxicity and the influence of metoprolol treatment on these variables. Adriamycin was administered to rats intravenously as a single dose of 6 mg/kg, and metoprol was continuously given by means of implanted osmotic pumps. beta-Adrenoceptor characteristics were measured by radioligand-binding experiments and by basal and stimulated adenylyl cyclase activity. Northern blot and dot blot analysis was used to quantify G-protein mRNA. It was shown that adriamycin did not induce any change in the total beta-adrenoceptor density, nor did the high affinity agonist binding to beta-adrenoceptor change. Adriamycin did not induce any alteration in the amount of mRNA encoding for stimulatory (Gs) or inhibitory (Gi) G-proteins. Also, basal and stimulated adenylyl cyclase activities were identical in the different experimental groups. In contrast, the Ca(2+)-ATPase was shown to increase in adriamycin-treated rats compared to control rats (45 +/- 3.8 versus 23 +/- 1.2 mumol Pi/mg/h, P less than .01). Metoprolol was shown to normalize this increase (29 +/- 2.1 mumol Pi/mg/h). Thus, it may be concluded that in experimental adriamycin-induced cardiotoxicity, despite Ca(2+)-overloading, the beta-adrenoceptor-G protein-adenylyl cyclase system remains intact. Metoprolol seems to prevent Ca(2+)-overloading independently of the beta-adrenoceptors studied here.

Increased Beta2-Adrenoceptors in Doxorubicin-Induced Cardiomyopathy in Rat

“…We showed that Dox-treatment did not change Gsα protein expression, as it was reported in other study [8], [11], but increased forskolin response, suggesting an increase in AC expression and/or activity. This surprising data contrasts with other studies which reported a decreased AC activity [41], [42] or no change [43]. However, those differences seem to be due to the cardiotoxicity level since the Dox cumulative doses used were 24, 24.75 and 6 mg.kg −1 , respectively.…”

Diabetes‐Induced Changes in the Gi‐Modulated Muscarinic Receptor‐Adenylyl Cyclase System in Rat Myocardium*

“…This is also supported by the finding of a single transcript of Gi-a 2 of 2.35 Kb in the Northern blot ( fig. 2), in accordance with the reported size of Gi-a 2 messenger ribonucleic acid in cerebral cortex (Eriksson et al 1992a), heart (Fu et al 1991b & c) and olfactory tissues (Jones & Reed 1987).…”

Localization of a functional autoimmune epitope on the muscarinic acetylcholine receptor-2 in patients with idiopathic dilated cardiomyopathy.

“…Moreover, the peptide we used corresponds to a sequence totally conserved in both humans and rats ( 15). Membrane proteins (75 Mg), prepared from normal rat ventricles as described ( 16), were subjected to electrophoresis on a 10% polyacrylamide gel in SDS and thereafter subjected to electrotransfer to nitrocellulose that was saturated with PMT buffer for 2 h at room temperature. The affinity-purified antibodies from patients and rabbits, and the mouse monoclonal antibody (mAb-35) ( 17) against calf brain muscarinic receptor used as a positive control, were incubated at 4°C overnight with the nitrocellulose strips.…”