EFFECTS OF THYROID-HORMONE ON CATECHOLAMINE AND ITS METABOLITE CONCENTRATIONS IN RAT CARDIAC-MUSCLE AND CEREBRAL-CORTEX

Clinical and experimental data suggest that thyroid hormone affects th e actions of catecholamine (CA). However, the serum or tissue levels o f CA during thyroid disorders have not been well defined. Accordingly, we investigated the levels of CA and their metabolites in the cardiac muscle, the cerebral cortex, and the plasma of rats with hyperthyroid ism and hypothyroidism vel sus euthyroid animals. The Neurochem analyz er system (ESA, Inc., Bedford, MA) was used in such determinations. Th e cardiac muscles of hyperthyroid rats exhibited a 16% decrease in the levels of 1-dopa, 3-methoxytyramine (3-MT) and homovanillic acid (HVA ) as compared with those in euthyroid rats. The levels of norepinephri ne (NE) in cardiac muscle of these rats increased significantly (5.2-f old) relative to the levels in euthyroid rats. ME was undetectable in the cardiac muscles of the hypothyroid rats. Epinephrine (E) and dopam ine (DA) were nor detected in the cardiac muscles of the rats with eit her thyroid disorder. Levels of E and 3,4-dihydroxymandelic acid (DOPE G) were detected only in the cerebral cortex of hyperthyroid rats. The cerebral cortex levels of 3-methyoxytyramine (3-MT), 3,4-dihydroxyphe nylacetic acid (DOPAC), metanephrine (MN), and homovanillic acid (HVA) were all significantly increased in the hyperthyroid versus the euthy roid rats. The cerebral cortex levels of DA, NE, normetanephrine (NMN) , and VMA in the hyperthyroid rats all showed a significant decrease. Levels of NE, NMN, and DOPAC in the cerebral cortex increased signific antly in the hypothyroid rats. The level of VMA was undetectable in ce rebral cortex of such animals. Data from studies on cardiac muscle and cerebral cortex indicate that the changes in CA and CA metabolites ar e responsible in part for the cardiovascular and the central nervous s ystem symptoms observed in hyperthyroidism and hypothyroidism.