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Regional changes in myocyte size and number in propranolol-treated hyperthyroid rats
A M Gerdes1, J A Moore, J M Hines
1Department of Anatomy, University of South Florida, Tampa.
Summary
Thyroid hormones cause cardiac myocyte hypertrophy by increasing cell size and length. Beta-adrenergic blockade with propranolol alters myocyte dimensions but does not prevent thyroid hormone-induced cardiac hypertrophy.
Area of Science:
- Cardiology
- Endocrinology
- Cell Biology
Background:
- Hyperthyroidism is associated with cardiac hypertrophy.
- Beta-adrenergic blockade is used to manage cardiovascular effects of hyperthyroidism.
Purpose of the Study:
- To investigate the effects of hyperthyroidism and beta-adrenergic blockade on cardiac myocyte structure.
- To determine if propranolol can prevent thyroid hormone-induced cardiac hypertrophy.
Main Methods:
- Isolated cardiac myocytes were prepared from control rats and rats treated with desiccated thyroid hormone (T), propranolol, or both (TP).
- Cell volume, length, and cross-sectional area were measured.
- Myocyte volume percent and cell number were determined morphometrically.
Main Results:
- Thyroid hormone treatment (T and TP) significantly increased myocyte volume and length in both ventricles.
- Myocyte hypertrophy was greater in the right ventricle compared to the left ventricle in T and TP groups.
- Propranolol alone increased myocyte length but not volume; it did not prevent thyroid hormone-induced hypertrophy.
Conclusions:
- Thyroid hormones induce cardiac myocyte hypertrophy by increasing both cell length and cross-sectional area.
- Propranolol influences myocyte dimensions but does not inhibit thyroid hormone-induced cardiac hypertrophy.