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Short- and long-term effects of neonatal hypo- and hyperthyroidism on coronary arterioles in rat
1Department of Physiology, Faculty of Medicine, University of Ottawa, Ontario, Canada.
Insights
Neonatal hyperthyroidism stimulated coronary arteriolar growth, while hypothyroidism attenuated it. Early hyperthyroid effects persisted, inhibiting later arteriolar growth despite increased cardiac mass.
Area of Science:
- Cardiovascular physiology
- Endocrinology
- Developmental biology
Background:
- Thyroid hormones play a critical role in neonatal development.
- Disruptions in thyroid hormone levels during the neonatal period can have long-lasting effects on organ development.
- Coronary arteriolar geometry is crucial for cardiac function and blood supply.
Purpose of the Study:
- To investigate the long-term effects of neonatal hypothyroidism and hyperthyroidism on coronary arteriolar geometry in Sprague-Dawley rats.
- To determine if early thyroid imbalances influence cardiac growth and vascular development.
- To assess the persistence of these effects after treatment cessation.
Main Methods:
- Newborn male Sprague-Dawley rats were treated with triiodothyronine (hyperthyroidism) or propylthiouracil (hypothyroidism) for 12 or 28 days.
- Coronary arteriolar and capillary dimensions were analyzed morphometrically.
- Long-term effects were evaluated 52 days after treatment cessation.
Main Results:
- Neonatal hyperthyroidism led to cardiac hypertrophy and increased total arteriolar length.
- Neonatal hypothyroidism attenuated cardiac growth and reduced total arteriolar length.
- After treatment cessation, hyperthyroid rats showed inhibited arteriolar growth relative to cardiac mass, while hypothyroid rats exhibited catch-up growth.
Conclusions:
- Neonatal hyperthyroidism promotes arteriolar and capillary growth, whereas hypothyroidism attenuates arteriolar growth.
- Early hyperthyroidism exerts a lasting inhibitory effect on subsequent arteriolar growth, independent of cardiac mass.
- Neonatal thyroid status significantly impacts long-term coronary vascular development.
Abstract:
Neonatal hypo- and hyperthyroid effects on coronary arteriolar geometry were examined in newborn male Sprague-Dawley rats treated for 12 or 28 days with either triiodothyronine or propylthiouracil. Long-term effects were assessed in weaned rats 52 days after stopping treatment. Influence of both neonatal conditions was more pronounced after 28 days. Neonatal hyperthyroidism induced cardiac hypertrophy; neonatal hypothyroidism attenuated cardiac growth. Hyperthyroid rats had similar arteriolar and capillary numerical densities and arteriolar length density but significantly greater (P < 0.05) total arteriolar length than control. Hypothyroid rats had similar arteriolar numerical and length densities, greater capillary numerical density (P < 0.05), but markedly lower total arteriolar length (P < 0.01) than control. Results suggest that neonatal hyperthyroidism stimulates arteriolar and capillary growth, whereas neonatal hypothyroidism attenuates arteriolar but not capillary growth. After cessation of treatment, total arteriolar length in previously hyperthyroid rats did not change despite increased cardiac mass, whereas previously hypothyroid rats demonstrated marked increases in both cardiac mass and total arteriolar length (P < 0.01). These results indicate a lasting inhibitory effect of early hyperthyroidism on subsequent arteriolar growth.