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Compensatory cell proliferation and growth in the rat heart after postnatal hypothyroidism
Insights
Hypothyroidism significantly stunts cardiac growth and cell proliferation in male rats. However, the developing heart shows remarkable recovery potential after thyroid hormone restoration.
Area of Science:
- Cardiovascular Physiology
- Developmental Biology
- Endocrinology
Background:
- Thyroid hormones are crucial for normal heart development.
- Hypothyroidism during early life can severely impact cardiac growth and function.
- Propylthiouracil (PTU) is a goitrogen used to induce hypothyroidism.
Purpose of the Study:
- To investigate the effects of induced hypothyroidism on cardiac growth and development in male rats.
- To assess the heart's capacity for rehabilitation and compensatory growth after cessation of PTU treatment.
Main Methods:
- Male rats were administered PTU from birth to induce hypothyroidism.
- Cardiac parameters including DNA, RNA, protein content, and heart weight were measured at postnatal days 10, 25, 50, and 90.
- PTU treatment was discontinued in some animals after 25 days to evaluate recovery.
Main Results:
- Hypothyroidism significantly reduced cardiac cell proliferation and growth (hyperplasia and hypertrophy).
- Inhibitory effects were more pronounced during the postweaning period, with heart growth halting.
- Following PTU withdrawal at day 25, significant cardiac rehabilitation occurred, with DNA content compensating fully by day 90.
Conclusions:
- The developing heart exhibits a substantial ability to recover from severe hypothyroid-induced retardation.
- Full compensation of cell number and near-complete compensation of cell growth were observed within two months post-treatment.
- Rehabilitation likely involves the restoration of thyroid hormones, growth hormone, and other growth factors.
Abstract:
Measurement of total DNA, RNA, and protein as well as weight of the heart in male rats at 10, 25, 50, and 90 postnatal days revealed that hypothyroidism, as induced by administration from birth of the goitrogen propylthiouracil (PTU), results in highly significant reductions in cardiac cell proliferation and cell growth. These inhibitory effects on hyperplastic and hypertrophic growths were less drastic during the suckling period than during the postweaning period. In the latter period, heart growth of the hypothyroid animals was found to remain at a standstill with regard to all the parameters measured. When, after 25 days of hypothyroidism, PTU treatment was discontinued, the retarded heart showed marked signs of rehabilitation and compensatory development. Indeed, by day 90, total DNA content had essentially compensated for its deficit but total RNA, protein content, and weight, though showing marked compensatory surges (from 80-90% deficit to 20-30%), were not yet fully compensated. The results clearly indicate that the growing heart has a marked ability to be rehabilitated from severe hypothyroid retardation, showing within 2 mo full compensation of cell number and nearly complete compensation of cell growth. It is suggested that rehabilitation of the heart is brought about by physiological restoration not only of the thyroid hormones but also of growth hormone and possibly other thyroid-dependent growth factors.