EPIDERMAL GROWTH-FACTOR INHIBITS RADIOIODINE UPTAKE BUT STIMULATES DEOXYRIBONUCLEIC-ACID SYNTHESIS IN NEWBORN RAT THYROIDS GROWN IN NUDE-MICE

We have studied the effect of altering the level of circulating epidermal growth factor (EGF) on the function and growth of newborn rat thyroids transplanted into nude mice. Preliminary studies confirmed that sialoadenectomy reduced circulating EGF levels in nude mice (from 0.17 ± 0.02 to 0.09 ± 0.02 ng/ml), and that ip injection of 5 μg EGF raised EGF levels (the peak level of 91.7 ± 3.3 ng/ml was achieved at 30 min, with a subsequent half-life of about 1 h). The radioiodine uptake by newborn rat thyroid transplants in the sialoadenectomized and sham-operated animals correlated inversely with the circulating EGF levels determined when the mice were killed (r = —0.99). Low-dose TSH treatment (0.1 μU/day) generally stimulated the radioiodine uptake, but high-dose TSH groups (100 μU/day) were not significantly different from the control group. The 5- day nuclear [3H]thymidine labeling index was 6.8 ± 0.5% in newborn rat thyroid transplants grown in sialoadenectomized animals, 13.1 ± 0.3% in sham-operated animals, and 16.8 ± 0.5% in nude mice receiving 5 μg EGF ip daily. In general, both lowdose and high-dose TSH promoted DNA synthesis under low EGF conditions but were ineffective in the presence of higher levels of EGF. Adult rat thyroid transplants showed no significant responses. Although sialoadenectomy may alter other factors besides EGF, it appears that changes in the levels of circulating EGF within the physiological range affect the function and growth of newborn rat thyroid transplants. Circulating EGF may play a role in thyroid maturation and may also be involved in the regulation of thyroid function throughout life. © 1990 by The Endocrine Society.