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Effects of thyroid deficiency and sympathectomy on cardiac enzymes
Abstract:
The effects of thyroid deficiency (Td) and of chemical sympathectomy (Sx) were studied on marker enzymes of energy metabolism in cardiac muscle of neonatal and of adult rats. Td prevented the normal development of neonatal body weight, relative heart mass, and cardiac levels of cytochrome c (-22%), citrate synthase (-27%), phosphofructokinase (-20%) and Mg2+- and Ca2+-ATPase activity of purified myofibrils (-33%, -44%). Exogenous thyroxin replacement restored those parameters studied to normal with the exception that it persistently elevated citrate synthase activity significantly above normal control levels. Responses similar to those of Td neonates occurred when adult rats were similarly treated. Sx produced no consistent effects on respiratory and glycogenolytic marker enzymes, but caused a 20% reduction in Ca2+-ATPase activity of both neonatal and adult cardiac myofibrils. These findings suggest that cardiac muscle cells require thyroxin for normal growth and enzyme development. Also, Sx may impair cardiac functional capacity by altering Ca2+ activity of actomyosin ATPase.
Insights
Thyroid deficiency (Td) impairs cardiac energy metabolism enzyme development in neonatal and adult rats. Sympathectomy (Sx) affects Ca2+-ATPase, potentially impacting heart function.
Area of Science:
- Cardiology
- Endocrinology
- Biochemistry
Background:
- Thyroid hormones are crucial for normal development and metabolic regulation.
- Cardiac muscle function relies on efficient energy metabolism and enzyme activity.
Purpose of the Study:
- To investigate the impact of thyroid deficiency (Td) and chemical sympathectomy (Sx) on cardiac energy metabolism enzymes.
- To assess the role of thyroxin in neonatal and adult rat heart development and enzyme expression.
Main Methods:
- Studied marker enzymes of energy metabolism in cardiac muscle of neonatal and adult rats under Td and Sx conditions.
- Administered exogenous thyroxin for replacement therapy in Td rats.
- Measured enzyme activities including cytochrome c, citrate synthase, phosphofructokinase, and Mg2+- and Ca2+-ATPase.
Main Results:
- Td significantly reduced body weight, relative heart mass, and key cardiac enzymes in neonates.
- Thyroxin replacement normalized most Td-affected parameters but persistently elevated citrate synthase.
- Sx reduced Ca2+-ATPase activity in both neonatal and adult cardiac myofibrils, with no consistent effects on other enzymes.
Conclusions:
- Cardiac muscle cells require thyroxin for normal growth and the development of energy metabolism enzymes.
- Sympathectomy may impair cardiac functional capacity by altering Ca2+-ATPase activity.