Short and long-term effects of neonatal hypo- and hyperthyroidism
on coronary arterioles in rat.
Heron, Marcia I., and Karel Rakusan.
Department of Physiology, Faculty of Medicine, University of
Ottawa, Ottawa, Ontario, K1H 8M5
APStracts 3:0143H, 1996.
Neonatal hypo- and hyperthyroid effects on coronary arteriolar
geometry were examined in newborn male Sprague-Dawley rats treated
for 12 or 28 days, with either triiodothyronine or propylthiouracil.
Long-term effects were assessed in weaned rats, 52 days after
stopping treatment. Influence of both neonatal conditions was more
pronounced after 28 days. Neonatal hyperthyroidism induced cardiac
hypertrophy; neonatal hypothyroidism attenuated cardiac growth.
Hyperthyroid rats had similar arteriolar and capillary numerical
densities, and arteriolar length density but significantly greater
(P<0.05) total arteriolar length than control. Hypothyroid rats
had similar arteriolar numerical and length densities, greater
capillary numerical density (P<0.05), but markedly lower total
arteriolar length (P<0.01) than control. Results suggest that
neonatal hyperthyroidism stimulates arteriolar and capillary growth,
whereas neonatal hypothyroidism attenuates arteriolar but not
capillary growth. Following cessation of treatment, total arteriolar
length in previously hyperthyroid rats did not change despite
increased cardiac mass, whereas previously hypothyroid rats
demonstrated marked increases in both cardiac mass and total
arteriolar length (P<0.01). These results indicate a lasting
inhibitory effect of early hyperthyroidism on subsequent arteriolar
growth.
Received 2 February 1996; accepted in final form 27 March 1996.
APS Manuscript Number H103-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96