Thyroid-pituitary function in eight anencephalic infants

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Abstract
The function of the thyroid pituitary axis was investigated in 8 anencephalic infants with no hypothalamus. Thyrotropin (TSH), thyroxine (T4), 3,5,3''-triiodothyronine (T3) and 3,3'',5''-triiodothyronine (reverse T3, rT3) were measured in the cord blood in 5 cases and during the first 4 h of life in 3 cases, TSH response to synthetic thyrotropin-releasing hormone (TRH [thyroliberin]) (200 .mu.g i.v.) was carried out in 2 cases and thyroid hormone response to bovine TSH (5 IU i.v.) was evaluated in 3 cases. The pituitary gland was found in all infants and the thyroid was normal both grossly and by microscopic sections. TSH levels at birth were normal, but there was no spontaneous post-delivery surge. T4 and T3 values at delivery were within normal range, but no T3 increase was present after birth. rT3 levels at birth were higher than normal in 3 cases. TRH administration caused a marked and rapid TSH release. Thyroid hormone response to TSH was normal. The present findings suggest that in the anencephalic fetus both pituitary TSH-secreting cells and the thyroid gland do develop despite the absence of the hypothalamus and are able to function if adequately stimulated.