AJP - Endocrinology and Metabolism, Vol 244, Issue 6 603-E606, Copyright © 1983 by American Physiological Society
Effect of changes in thyroid status on tissue respiration in fetal and newborn sheep
A. H. Klein, A. Reviczky, J. F. Padbury and D. A. Fisher
The effect of both exogenous and endogenous changes in thyroid status on in
vitro tissue respiration and thermogenic enzymes
(sodium-potassium-adenosine triphosphatase and alpha-glycerophosphate
dehydrogenase) was studied in fetal and newborn sheep. Oxygen consumption
of liver and brain increased from 25 +/- 4.1 and 58.5 +/- 2.8 microliters
O2 X 100 mg-1 X h-1, respectively, in tissues from unthyroidectomized fetal
animals at 136-140 days gestation to 60 +/- 4.2 and 72 +/- 1.5 microliters
O2 X 100 mg-1 X h-1 in tissues from unthyroidectomized newborn lambs
between birth and 7 days of age. The physiological changes in thyroid
function that normally occur at birth resulted in a mean (+/- SE) plasma
triiodothyronine (T3) concentration of 563 +/- 39 ng/dl in the newborn
lambs compared with 39 +/- 8 ng/dl in the fetal animals. Kidney respiration
and thermogenic enzyme activities in the several tissues studied did not
change. Liver, kidney, and brain respiration and thermogenic enzymes from
T3-treated thyroidectomized fetal and newborn lambs were not increased
(compared with untreated thyroidectomized animals) despite a marked
increase in plasma T3 concentrations. Conclusions are that 1) liver, kidney
cortex, and frontal brain cortex in the fetal and newborn lamb are
relatively insensitive to the calorigenic effect of thyroid hormones, and
2) a perinatal increase in hepatic and cerebral respiration occurs in
newborn animals (compared with fetal animals) but is probably not due
solely to perinatal increases in thyroid hormones.
