Activity of receptors coupled to guanine nucleotide binding regulatory protein in doxorubicin induced cardiomyopathy.

Study objective - The aim was to study the activity of receptors coupled to guanine nucleotide binding regulatory proteins (G proteins) in doxorubicin induced cardiomyopathy, with special attention to G proteins, beta adrenoceptors, muscarinic receptors, and adenylyl cyclase. Design - Messenger RNA of G proteins, densities and high affinity agonist binding of beta adrenoceptors and muscarinic receptors, activity of adenylyl cyclase, calcium influx, and in vivo lipid peroxidation were determined before, in the early stage, and in the later stage of doxorubicin cardiomyopathic heart failure. Subjects - Sprague-Dawley rats between 150-200 g were used. Doxorubicin was given intravenously at two doses of 4 mg.kg-1 and 6 mg.kg-1 every third week (1st, 4th, 7th week) for nine weeks. Doxorubicin treated rats plus corresponding controls were killed at 3 weeks (n = 7), 6 weeks (n = 7), and 9 weeks (n = 6), respectively. Measurements and main results - Northern blot and dot blot hybridisations of the total RNA revealed that messenger RNA of both stimulatory and inhibitory G proteins were identical between doxorubicin treated rats and controls. No alterations in the densities of beta adrenoceptors and muscarinic receptors were observed, neither did the high affinity agonist binding of beta adrenoceptors and muscarinic receptors change. Furthermore, modulation of adenylyl cyclase was unimpaired. In contrast, Ca2+-ATPase and serum water soluble fluorescent substance, a product of in vivo lipid peroxidation, were shown to increase dramatically in doxorubicin treated rats (4 mg.kg-1 for 6 and 9 weeks, 6 mg.kg-1 for 3, 6 and 9 weeks) as compared with corresponding controls. Conclusions - The findings suggest that, despite increased calcium influx and lipid peroxidation in doxorubicin induced cardiomyopathy, the activity of receptors coupled to G proteins remained normal.