Chronic β-Adrenergic Receptor Stimulation Enhances the Expression of G-Protein Coupled Receptor Kinases, GRK2 and GRK5, in Both the Heart and Peripheral Lymphocytes

Background Enhanced expression of G protein-coupled receptor kinase (GRK) has been reported in failing hearts and in the present study the stability of enhanced GRK mRNA expression, and the correlation between the expression level of GRK mRNA in peripheral lymphocytes and in the heart were both evaluated. Methods and Results Isoproterenol was injected into rats for 2 weeks, and then GRK5 mRNA was assessed by quantitative reverse transcriptase-palymerase chain reaction. An enhanced expression of cardiac GRK5 mRNA was observed even after 4 weeks of recovery. The isoproterenol-induced increased expression of GRK2 and GRK5 mRNA was equally observed in the heart and lymphocytes, and there was a close correlation between the heart and lymphocytes in the level of expression of each GRK mRNA. Conclusions The GRK mRNA level is maintained at a high level for a long period without continuous β-adrenergic receptor stimulation. The level in circulating lymphocytes could be used as a surrogate marker to estimate the level of cardiac GRK expression and, presumably, the β-adrenergic receptor function of cardiomyocytes. (Circ J 2005; 69: 987 - 990)