AJP - Endocrinology and Metabolism, Vol 248, Issue 3 381-E387, Copyright © 1985 by American Physiological Society
Compensatory cell proliferation and growth in the rat heart after postnatal hypothyroidism
R. Moussavi, E. Meisami and P. S. Timiras
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.
