Physiologic thyroid activation in normal early pregnancy is induced by circulating hCG.
In normal early pregnancy, serum free thyroxine (T4) increases and serum TSH decreases, indicating that the thyroid gland is activated physiologically. To identify the factor responsible for this thyroid activation, we measured the serum thyroid-stimulating activity in comparison with the serum level of hCG in 39 normal women in early pregnancy. Serum thyroid-stimulating activity was measured by a sensitive cyclic adenosine 3',5'-monophosphate (cAMP) accumulation assay using a rat thyroid cell line (FRTL-5). Thyroid-stimulating activity was detected in 37 women (95%), and the activities of individuals correlated positively with their serum free T4 levels (r = 0.474; P less than .01) and negatively with their serum TSH levels (r = -0.376; P less than .02). Moreover, serum thyroid-stimulating activity correlated closely with the serum hCG level (r = 0.741; P less than .001), but was completely abolished by pre-treatment of the sera with hCG antibodies. These data indicate that in normal early pregnancy, the thyroid gland is physiologically activated by serum hCG, which has intrinsic thyroid-stimulating activity.
Kimura
M
M
Department of Laboratory Medicine, Osaka University Medical School, Japan.
Amino
N
N
Tamaki
H
H
Mitsuda
N
N
Miyai
K
K
Tanizawa
O
O
D000818:Animals; D002460:Cell Line; D006063:Chorionic Gonadotropin / Q000097:blood*; D000242:Cyclic AMP / Q000096:biosynthesis; D005260:Female; D006801:Humans; D011247:Pregnancy / Q000097:blood / Q000502:physiology*; D051381:Rats; D013961:Thyroid Gland / Q000378:metabolism / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
D006063:Chorionic Gonadotropin; D013972:Thyrotropin; D000242:Cyclic AMP; D013974:Thyroxine