EVIDENCE FOR THE PRESENCE OF FUNCTIONAL THYROTROPIN RECEPTOR IN CARDIAC-MUSCLE

There is increasing evidence that the membrane-bound thyrotropin recep tor (TSHR) may be mediating clinically important direct effects of thy rotropin (TSH) and of TSHR antibodies (TSHRab) in extra-thyroidal tiss ues. TSHR mRNA has formerly been detected in thyroid, retroorbital mus cle and fibroblasts, peripheral lymphocytes and rodent fat, It is well known that thyroid disease may aggravate or induce heart disease, but the pathophysiological role of TSH and TSHRab is not clear. The aim o f this study was to investigate if TSHR is present in cardiac muscle. Reverse transcriptase polymerase chain reactions revealed TSHR in huma n heart and Northern blot on extracted RNA showed a RNA species of 4.4 kb. TSH stimulation of cultured mouse AT-1 cardiomyocytes elevated th e levels of intracellular second messenger 3',5'-cyclic AMP. This effe ct of TSH could be inhibited by TSHR antibodies. In solution hybridiza tion levels of TSHR mRNA in AT-1 cells were 50% of mRNA in crude mouse heart. In conclusion functional TSHR is present in cardiomyocytes. (C ) 1995 Academic Press, Inc.