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<p>Most small mammalian hibernators spend the hibernation season cycling between bouts of torpor (with low body temperature (T<sub>b</sub>) approximating ambient temperature (T<sub>a</sub>), depressed heart and oxygen consumption rates as low as 1% active rates) and interbout arousals (IBA) where animals will spontaneously and rapidly arouse from torpor and resume most physiological functions. Kidneys are involved in numerous physiological functions including filtering the blood of metabolic waste. Due to the dramatic metabolic depression experienced during torpor and previous limitations in methods, studies inadequately addressed filtration <i>during</i> torpor. Here, we directly monitored clearance of sinistrin from ground squirrel circulation for up to 45&#xa0;h during torpor bouts using transdermal fluorometry. In active squirrels (both summer active and interbout aroused), clearance by the kidneys was rapid with a clearance half-life (t<sub>1/2</sub>) of 47.8 ± 5.4 and 73.4 ± 7.9&#xa0;min, respectively. In contrast, clearance by the kidneys in torpid squirrels held at T<sub>a</sub>= 4&#xa0;°C was greatly reduced, but measurable, with t<sub>1/2</sub> of 7,103 ± 1,073&#xa0;min (~ 97 to 149-fold increase in clearance time vs. active squirrels). Consistent with predictions based on metabolism, clearance by the kidneys during torpor at T<sub>a</sub>=12&#xa0;°C resulted in much faster clearance times than at T<sub>a</sub> = 4&#xa0;°C (T<sub>1/2</sub>= 2,761 ± 375&#xa0;min; 2.57-fold increase vs. 4&#xa0;°C; Q<sub>10</sub> = 3.26). We demonstrate that hibernators do not completely cease excretion functions during torpor but that clearance quickly commences even at low temperatures as soon as the squirrel begins to arouse.</p>

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Glomerular filtration by the kidney nearly arrests during torpor and is rapidly restored as hibernating ground squirrels begin to arouse

  • 期刊论文

  • 发表日期：

    2025年12月15日

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  • Michael D. Treat,
  • Gilbecca R. Smith,
  • Frank van Breukelen

摘要

Most small mammalian hibernators spend the hibernation season cycling between bouts of torpor (with low body temperature (Tb) approximating ambient temperature (Ta), depressed heart and oxygen consumption rates as low as 1% active rates) and interbout arousals (IBA) where animals will spontaneously and rapidly arouse from torpor and resume most physiological functions. Kidneys are involved in numerous physiological functions including filtering the blood of metabolic waste. Due to the dramatic metabolic depression experienced during torpor and previous limitations in methods, studies inadequately addressed filtration during torpor. Here, we directly monitored clearance of sinistrin from ground squirrel circulation for up to 45 h during torpor bouts using transdermal fluorometry. In active squirrels (both summer active and interbout aroused), clearance by the kidneys was rapid with a clearance half-life (t1/2) of 47.8 ± 5.4 and 73.4 ± 7.9 min, respectively. In contrast, clearance by the kidneys in torpid squirrels held at Ta= 4 °C was greatly reduced, but measurable, with t1/2 of 7,103 ± 1,073 min (~ 97 to 149-fold increase in clearance time vs. active squirrels). Consistent with predictions based on metabolism, clearance by the kidneys during torpor at Ta=12 °C resulted in much faster clearance times than at Ta = 4 °C (T1/2= 2,761 ± 375 min; 2.57-fold increase vs. 4 °C; Q10 = 3.26). We demonstrate that hibernators do not completely cease excretion functions during torpor but that clearance quickly commences even at low temperatures as soon as the squirrel begins to arouse.