THE EFFECTS OF HYPOTHERMIA ON RENAL-FUNCTION AND HEMODYNAMICS IN THE RAT

The effects of 1-2 h of hypothermia at 28 degrees C and rewarming on r enal function were investigated in anaesthetized rats, using conventio nal clearance methods and the micropuncture technique. Renal blood flo w (RBF) decreased from 7.3 +/- 0.51 mL min(-1) at 37.5 degrees C (cont rol) to 4.0 +/- 0.47 at 28 degrees C, with almost complete restoration to 6.9 +/- 0.59 mL min(-1) after rewarming. Systemic blood pressure r emained essentially unaltered. The RBF reduction seen during hypotherm ia was due to a 75% increase in vascular resistance, mainly attributab le to constriction of the afferent arteriole and increased blood visco sity. This was accompanied by a decline in glomerular capillary pressu re from 56.7 +/- 0.6 to 46.4 +/- 1.3 mmHg, overshooting to 59.0 +/- 0. 7 mmHg. The glomerular filtration rate (GFR) decreased from 1.1 +/- 0. 08 to 0.6 +/- 0.04 mL min(-1), returning to 1.0 +/- 0.07 after rewarmi ng, a pattern also observed for single nephron GFR. This resulted from a decrease in net driving force for glomerular filtration, whereas th e filtration coefficient was not affected. Both proximal and distal tu bular fluid flow decreased, but fractional reabsorption remained uncha nged. In contrast, urine flow increased from 1.8 +/- 0.16 to 5.7 +/- 1 .08 mu L min(-1), returning to 2.1 +/- 0.18, the increase during hypot hermia mainly resulting from a disproportionately reduced fluid reabso rption beyond the mid-distal tubule.