AMNIOTIC AND ALLANTOIC FLUID CONCENTRATIONS OF THYROXINE, 3,3',5'-TRI-IODOTHYRONINE, 3,3'-DI-IODOTHYRONINE AND 3',5'-DI-IODOTHYRONINE IN THE PIG DURING THE PERIOD OF GESTATION

Thyroxine (T-4), 3,3',5'-tri-iodothyronine (reverse T-3; rT(3)) and di -iodothyronines (3,3'-T-2 and 3',5'-T-2) were measured in pig amniotic fluid (AF) and allantoic fluid (Al) between 32 and 113 days of normal pregnancy. Low but measurable quantities of T-4 in AF and Al (2.1 +/- 0.3 and 3.2 +/- 0.5 nmol/l respectively) were found before the onset of fetal thyroid gland function, which indicates the maternal source o f T-4. The presence of rT(3) (55.8 +/- 4.1 pmol/l in AF and 49.8 +/- 5 .3 pmol/l in Al), 3,3'-T-2 (45.5 +/- 0.6 pmol/l in AF and 49.2 +/- 9.2 pmol/l in Al) and 3',5'-T-2 (20.8 +/- 2.6 pmol/l in AF and 24.0 +/- 2 .2 pmol/l in Al) may be attributed to the monodeiodinase system alread y active in fetal pig tissues in early pregnancy, as demonstrated prev iously. T-3 concentration was undetectable in both AF and Al. An appro ximately twofold increase in the levels of T-4, rT(3) and T(2)s in AF and Al at mid-gestation was observed.