Te. Tomasi et al., THYROID-HORMONE CONCENTRATIONS IN BLACK BEARS (URSUS-AMERICANUS) - HIBERNATION AND PREGNANCY EFFECTS, General and comparative endocrinology, 109(2), 1998, pp. 192-199
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.