MCNABB, F.M.A.; QUERAL-KIRKPATRICK, L.T.; Virginia Tech; Virginia Tech: Endocrine Disruption and Thyroid Adaptation in Quail

We studied the effects of sustained ammonium perchlorate (AP) exposure (.013-4,000 mgAP/l [ppm] in drinking water) for up to 8 weeks on chicks and adult bobwhite quail. AP competitively inhibits iodide uptake into the thyroid gland. We measured plasma thyroid hormones (THs) as indicators of organismal thyroid status, thyroid gland (TG) weight as an indicator of hypothalamic-pituitary-thyroid (HPT) axis activation and TG-TH content as an indicator of TH stores. As we previously observed in other studies, the order of thyroid variables from most to least sensitive is: TG-TH content > TG weight ≥ plasma T4. Bobwhite chicks, exposed to AP for 2 weeks had significantly decreased TG-TH content at ≥.05 ppm but did not exhibit organismal hypothyroidism except at ≥500 ppm. Samplings at 4 and 8 weeks suggested that thyroid function of chicks adapts to AP exposure with complete restoration of TG-TH content in the .013-5.0 ppm AP range and partial restoration in the 50-250 ppm AP range. There was no evidence of thyroid adaptation to ≥500 ppm AP in chicks. In contrast to chicks, adult bobwhites were much slower to exhibit AP effects on thyroid function and tolerated higher AP exposures (up to 8,000ppm). There was no evidence of adaptive responses in adults during the 8 week exposures used in these studies. It is often thought that developing animals are more vulnerable to endocrine disrupting chemicals than are adult animals. Our results in chicks suggest that the developing thyroid system has some plasticity for adapting to and compensating for the relative iodide deficiency effects of AP exposure. Supported by SERDP #CU1242.