AJP - Cell Physiology, Vol 263, Issue 4 C788-C793, Copyright © 1992 by American Physiological Society
Effect of thyroid status on the expression of metabolic enzymes during chronic stimulation
D. A. Hood, J. A. Simoneau, A. M. Kelly and D. Pette
Fakultat fur Biologie, Universitat Konstanz, Federal Republic of Germany.
The effect of thyroid status on the expression of cytochrome c oxidase
(CYTOX) and the activities of citrate synthase (CS) and phosphofructokinase
(PFK) were examined in chronically stimulated (10 Hz; 35 days) and
contralateral, nonstimulated rat tibialis anterior muscle of hypothyroid,
hyperthyroid, and euthyroid animals. Stimulation increased CYTOX activity
by 2.7-, 3.2-, and 4.9-fold in hyperthyroid, euthyroid, and hypothyroid
animals, respectively, to similar absolute values. CS displayed similar
increases. Stimulation reduced PFK activity in hypothyroid and euthyroid
animals to 45% and 60% of control values. This effect was abolished with
hyperthyroidism. Thus stimulation and thyroid hormone act antagonistically
on PFK activity. Stimulation increased CYTOX subunit III (mitochondrially
encoded) mRNA by 2.5- and 2.9-fold in hyperthyroid and euthyroid animals.
Similar increases were observed in the nuclear-encoded mRNAs of CYTOX
subunit VIc in euthyroid muscle. In hyperthyroid and euthyroid conditions,
the mRNA changes paralleled the increases in enzyme activity. In
hypothyroid muscle, the increase in mRNA was less for subunit VIc than III,
suggesting that hypothyroidism upsets the coordinate expression of nuclear
and mitochondrial genes. Further, the increases in CYTOX activity exceeded
that of both subunit mRNAs in hypothyroid muscle.(ABSTRACT TRUNCATED AT 250
WORDS)
