HIBERNATION AND THE ENDOCRINES1

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Abstract
The 13-lined ground squirrel, Citellus tridecemlineatus, was found to hibernate more consistently under exptl. conditions of dehydration to a moderate degree. During the breeding season, hibernation could not be induced, but shortly afterward there was maximal tendency to hibernate which persisted until the onset of genital enlargement. From the time of vaginal swelling and testicular descent the tendency to hibernate diminished until sexual activity occurred. During the breeding season, extirpation of the pituitary converted these animals into poikilotherrns, while removal of thyroid, adrenals or gonads was without significant effect. Substitution therapy during the poikilothermic season with pituitary preps. resulted in transient homiothermism. Similar results were obtained with thyroid preps., but gonadotropic pituitary extracts, corticoadrenal extracts and sex hormones were without effect. These findings suggested inactivity of the pituitary as the primary factor responsible for the phenomenon of hibernation.