Meeting Abstract
P2.93 Friday, Jan. 4 Development of a thyroid stimulating hormone challenge test in red drum (Sciaenops ocellatus) MILLER, T.C.*; MACKENZIE, D.; JAQUES, S.; Department of Biology, Texas A&M University; Department of Biology, Texas A&M University; Texas Veterinary Medical Diagnostic Laboratory tcmiller@tamu.edu
The existence of well-established peripheral mechanisms for regulation of thyroid hormone delivery to targets has called into question the significance of the hypothalamic-pituitary axis as a primary regulator of circulating thyroid hormone concentrations in fish. The objective of this study was to develop a thyroid stimulating hormone (TSH) challenge test to serve as a means for evaluating thyroid sensitivity to TSH in red drum, a perciform fish demonstrating dynamic daily thyroxine (T4) cycles. A single injection of bovine thyroid stimulating hormone (bTSH) significantly increased serum bTSH and T4 levels by 30 minutes. bTSH peaked at two hours, declined significantly by 5 hours, and was only slightly elevated above controls by 8 hours. In contrast, T4 remained elevated for up to 11 hours while T3 showed no consistent changes. Doses ranging from 0.6 to 5 mU bTSH/gram body weight elicited a dose-dependent increase in T4 at five hours post-injection. Replication of these experiments revealed a significant decrease in sensitivity to the same doses of bTSH, which was not related to previous treatment with bTSH, animal size, or origin, but did vary with diet. The red drum TSH challenge test may thus provide a useful tool for evaluating changes in thyroid sensitivity to stimulation under imposed aquacultural conditions or in response to endocrine-disrupting chemicals.
