Thyroxine and 3,5,3'-triiodothyronine production, metabolism, and distribution in pregnant rat near term.
In the pregnant rat near term thyroxine (T4) and 3,5,3'-triiodothyronine (T3) concentrations are lower in plasma and extrathyroidal tissues, except T3 in the brain. To study the changes in T4 and T3 kinetics a bolus injection of [125I]T4 and [131I]T3 was administered to nonpregnant controls and rats 14 and 19 days pregnant. Physiological parameters of the production, interpool transport, distribution, and metabolism of T4 and T3 were estimated by means of a three-compartment model. The production and partition of T4 remained unchanged during pregnancy. The total distribution volume of T4 was enlarged. On day 19 the plasma clearance rate was doubled, and transport to the fast pool was more than tripled. The rate of production of T3 was slightly diminished. The plasma clearance rate was increased, but no changes were found in the interpool transport rates. These results suggest that in the pregnant rat near term the increased transport of T4 is responsible for the distribution of the available T4 between the maternal and the fetal compartment.
Versloot
P M
PM
Department of Human and Animal Physiology, Agricultural University, Wageningen, The Netherlands.
Gerritsen
J
J
Boogerd
L
L
Schr oder-van der Elst
J P
JP
Van Der Heide
D
D
D000818:Animals; D001692:Biological Transport; D005260:Female; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*
D014284:Triiodothyronine; D005993:Glycerolphosphate Dehydrogenase; D013974:Thyroxine