Adrenal activity in the female lizard Lacerta vivipara Jacquin during artificial hibernation

The variations of interrenal activity were investigated in captive female Lacerta vivipara submitted to artificial hibernation (4 months at 6 degrees) and compared to data obtained in nonhibernating females. Plasma corticosterone levels reached 25 ng/ml during the prehibernal period. During the first day following the transfer to cold conditions, an initial significant peak of plasma corticosterone was observed (up to 63 ng/ml). A second, more gradual, but also significant increase was observed thereafter and levels remained maximum during the two first months of artificial hibernation (75 ng/ml). The circulating levels of corticosterone then decreased gradually. At the time of transfer to warm conditions, a third significant peak of corticosterone was observed (up to 82 ng/ml). The minimal values (15 ng/ml) previously described during vitellogenesis were reached within 1 week. High corticosterone levels appeared to be actually related to the "hibernation state" since they were also observed in hibernating males and not in nonhibernating females. In order to explain the pattern of plasma corticosterone, variations of adrenal sensitivity to synthetic ACTH 1-39 were examined in vitro, using a perifusion system technique. Surprisingly, ACTH-induced stimulation of corticosterone and aldosterone release was significantly reduced during hibernation, whatever the temperature of the perifusion bath (30 or 6 degrees). Nevertheless, a fourfold increase in the half-life of injected tritiated corticosterone was observed during hibernation which likely contributes to maintain high levels of corticosterone despite a low production rate of the hormone.