Objective    To study the expressions of tyrosine hydroxylase (TH) and growth associated protein 43 (GAP-43) in cardiac atria and pulmonary vein

and to explore the effects of thyroid hormone on nerve and tissue remodeling of cardiac atria and pulmonary vein.     Methods    Twe

nty New Zealand rabbits were randomly divided into two groups: a control group (n=10) and an experimental group (n=10). A hyperthyroidism animal model was established by levothyroxine (L-Thy) peritoneal injection in the experimental group [50 μg/(kg·d)×28 d

]

. All the rabbits were followed up for 4 weeks. On the 0th

7th

14th

21st

and 28th day after L-Thy injection

blood samples were collected from the marginal ear vein and used to test serum TT

3

and TT

4

levels by radioimmunoassay

and the heart rate

body weight

and body temperature of the rabbits were measured at the same time points. The posterior walls of cardiac atria and the pulmonary vein tissues were collected at the 28th day. The morphologies of cardiac atria and pulmonary vein were observed by light microscopy. The cardiomyocyte diameter was measured. The collagen volume fraction (CVF) was measured by a pathological image analysis system after Van Gieson (VG) staining. The GAP-43 expression in left and right atria (LA and RA) as well as in pulmonary vein (PV) was semi-quantified by immunohistochemistry. The mRNA expression of TH and GAP-43 in left and right atria as well as in pulmonary vein was semi-quantified with RT-PCR.     Results    The experimental group possessed increased cardiomyocyte diameter when compared with the control group (LA 9.58±0.57  vs 4.79±0.31 mm; RA 8.19±0.65 vs 4.67±0.29 mm)

and increased CVF (LA 6.71±0.11 vs  0.36±0.06; PV 4.29±0.12 vs 0.19±0.01; RA 4.62±0.40 vs 0.3±0.12). Besides

the experimental group also had a significantly higher protein level of GAP-43 (LA 0.46±0.12 vs 0.15±0.04; PV 0.28±0.10 vs 0.10±0.04; RA  0.34±0.09 vs 0.13±0.05) (P0.01)

as well as significantly higher mRNA levels of TH (LA  1.62±0.2 vs 0.77±0.08; PV 1.23±0.13 vs 0.68±0.09; RA 1.02±0.15 vs 0.48±0.10) and GAP-43 (LA 0.61±0.17 vs 0.27±0.06; PV  0.34±0.14 vs 0.20±0.09; RA 0.42±0.15 vs 0.22±0.07) (P0.01) in cardiac atria and pulmonary vein.     Conclusion    L-Thy can induce the morphological changes of cardiomyocytes

myocar

dial interstitial fibrosis and sympathetic nerve hyperplasia in cardiac atria and pulmonary vein. The nerve remodeling of cardiac atria and pulmonary vein may correlate with the pathogenesis of atrial fibrillation related to hyperthyroidism.