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Biology | Life Sciences


Clark Cotton, Biology


During bouts of torpor hibernating animals have greatly reduced metabolic rates leading to profound decreases in body temperature and blood pressure. As a result of these conditions, kidney filtration and the ability to concentrate urine cease. Once a week, however, hibernators rewarm to euthermic body temperatures and regain kidney function. This is associated with rapid changes in extracellular osmotic gradients within the kidney, a remarkable feat but one that is potentially damaging to kidney cells. While hibernators deal with this stress by up-regulating expression of heat shock proteins (HSP’s) and protective organic osmolytes, little research has been done to see if hibernating animals can achieve and cope with similar situations during the summer. To address this question we placed a typical hibernator (I. tridecemlineatus) on various water intake regimes over the summer to experimentally manipulate vertical osmotic gradients in the kidney, represented by changes in urea concentration. We then measured renal expression of HSP 70 in response to changes in the vertical gradient. Animals rapidly altered the vertical gradients in their kidneys in response to different water intake regimes. This was accompanied by large changes in urine volume and concentration, and maintenance of serum hydromineral homeostasis. Unlike hibernation however, HSP70 expression was up-regulated in response to loss, rather than gain, of vertical osmotic gradients. This difference may be due to an interplay between HSP70 and protective organic osmolytes. Future studies will examine this relationship in closer detail and also evaluate the response of non-hibernating species to similar conditions.

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