AJP - Cell Physiology, Vol 236, Issue 1 30-C34, Copyright © 1979 by American Physiological Society
Effects of thyroid deficiency and sympathectomy on cardiac enzymes
K. M. Baldwin, P. J. Campbell, A. M. Hooker and R. E. Lewis
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.
