Mechanisms responsible for decreased glomerular filtration in hibernation and hypothermia

Mechanisms underlying the elimination or marked depression of renal function in hibernation and hypothermia were investigated through measurements of blood pressure, heart rate, red blood cell and plasma volumes, and relative distribution of cardiac output. Hamsters (Mesocricetus auratus) were made hypothermic (rectal temperature (Tre), 7 degrees C) by exposure to helox and cold, or permitted to hibernate with several weeks of cold exposure (Ta approximately 5 degrees C). Mean arterial pressure, 120 Torr in normothermic control animals, demonstrated a 55% and 60% decrease during hibernation and hypothermia, respectively. As the animals rewarmed from hypothermia or aroused from hibernation, blood pressure increased rapidly at 8-12 degrees C, more gradually at 12-17 degrees C, and plateaued thereafter. Blood pressure rapidly returned to near control levels whereas heart rate remained at less than one-half control value at the highest temperature examined. Red blood cell volume, 26.2 +/- 0.6 ml/kg body wt in the control animals appeared unaffected by hypothermia. Plasma volume, by contrast, decreased from control values of 33.0 +/- 0.8 to 21.3 +/- 0.6 ml/kg body wt in hypothermia, a decrease of approximately 35%. Distribution of cardiac output to various organs in hibernation and hypothermia followed a similar pattern. Relative flow to the heart, lung, diaphragm, and brown fat increased while the fraction distributed to the visceral organs appeared to decrease. The normothermic control kidney received approximately 16% of the cardiac output while the hibernating and hypothermic kidneys received approximately 10% and 6%, respectively. The data are discussed in terms of the determinants of glomarular filtration rate and explain, in part, the elimination or marked reduction in renal function observed in depressed metabolic states.