Midtrimester thyroidectomy in the ovine fetus.

Six lamb fetuses at 63-101 days gestation had thyroidectomy (Thx) and were investigated at term for weights, radiologic study, serum thyroxine (T4), and thyroid-stimulating hormone concentrations (TSH), electron-microscopic lung examination, acid base, blood flow, EEG, and brain metabolism. Compared to age-matched controls, body weight was significantly reduced (P less than .025). Brain and lung weights were reduced but not significantly. Brain weight as a percent of body weight was significantly increased in Thx fetuses (Thx = 1.85% +/- 0.18; control = 1.41% +/- 0.08; P less than .025). Hemoglobin was reduced (P less than .025), as was O2 content (P less than .005) and cerebral blood flow (P less than .05). Fetal T4 was low (Thx = 4.1 +/- 1.7 microgram %, control = 9.4 +/- 1.3 microgram %); (P less than .05). Fetal Thx cortisol, calcium, phosphate, glucose, lactate, pH, pO2, pCO2, O2 saturation, heart rate, and blood pressure remained unchanged. Thx-fetal brain O2 consumption and glucose consumption, as well as lactate production, were unchanged. EEG showed no consistent pattern of change regarding maturity, but did show immaturity with the two lowest T4 levels. Bone microradiographs showed growth and maturity retardation, specifically delayed epiphyseal closure, endochrondral ossification, and lack of secondary ossification centers in Thx fetuses. Electron-microscopic examination of lung showed Thx fetuses had fewer lamellar bodies in type II cells, fewer type II cells, and more glycogen granules. Thx causes fetal reduction of T4 and anemia, delays lung maturation and bone growth and maturation.(ABSTRACT TRUNCATED AT 250 WORDS)