Thyroid Histology and Hormone Concentrations in the Bowhead Whale Interpreted with Respect to Histologic, Seasonal, and Contaminant-Related Factors
Abstract
Thyroid activity was investigated in the bowhead whale (Balaena mysticetus) during the spring and fall phases of their annual migration from the Bering Sea to the Beaufort Sea. Histologic sections from thyroid glands (n=27) were examined in conjunction with serologic thyroid hormone analyses (n=50). Serum was assayed for triiodothyronine (total [tT3], free [fT3]) and thyroxine (total [tT4], free [fT4]) via radioimmunoassay. Thyroid tissue was assessed via light microscopy and the utilization of an epithelial-follicular index (EFI, via methodology developed by Sorkin, 1971).
Results show no effect of age, sex, or season on serum hormones. However, a seasonal effect was noted on the epithelial follicular index (EFI), with a significant difference in the height of the follicular lining being noted in spring (versus fall) samples. All results were compared to additional data collected in these whales, including vitamin A and E and organochlorine concentrations in the liver, serum, and blubber.