THYROID-HORMONE CONCENTRATIONS IN BLACK BEARS (URSUS-AMERICANUS) - HIBERNATION AND PREGNANCY EFFECTS

Previous studies on thyroid hormones in hibernating bears have used ve ry few sampling periods, so that the time course of any change is poor ly understood. In this study, plasma sampled from pregnant and nonpreg nant black bears before and during hibernation (16 samples each at 10- day intervals) was assayed by radioimmunoassay for concentrations of t hyroxine (T-4) and triiodothyronine (T-3). Only free T-4 showed a diff erence (P = 0.019) between females that produced cubs and those that d id not, but this appeared to be due to higher preimplantation values. Free T-3, total T-3, and free T-4 varied (P = 0.001, 0.038, 0.002, res pectively) among sampling periods: during December, bears had depresse d concentrations. These lowered concentrations were maintained during hibernation for the free hormones. Our data confirm previous work show ing that food restriction and/or physiological preparation for hiberna tion is coincident with depressed plasma concentrations of thyroid hor mones. Hormonal changes associated with pregnancy were minor. (C) 1998 Academic Press.