Cold acclimation-induced increase of systolic blood pressure in rats is associated with volume expansion

To investigate the mechanisms of cold-induced hypertension, the systolic bl ood pressure (SBP) and average daily water consumption were measured weekly in 6-month-old male Wistar rats; they were subsequently acclimated to ther moneutrality (26 degrees C for 7 weeks), to cold temperature (6 degrees C f or 9 weeks), and then again reacclimated to 26 degrees C for 5 weeks. Circu lating plasma volume and whole blood viscosity were measured in subgroups o f rats at the end of acclimation to 26 degrees C after 2 days, after 1, 6, and 8 weeks of cold, and after 2 and 5 weeks of rewarming. The control valu es obtained at the end of thermoneutral period were: SEP = 130.8 +/- 18.6 m m Hg, plasma volume = 41.9 +/- 4.64 mL/kg, whole body viscosity at shear ra te of 22.5 per sec = 6.7 +/- 0.48 cps, and daily water consumption = 42.25 +/- 16.81 mL. After 48 h of cold exposure there was almost a 50% increase i n plasma volume that persisted to a lesser degree throughout the whole peri od of cold exposure (P < .05). After 2 weeks of cold exposure the daily wat er consumption increased and SEP began to increase. After 6 weeks of cold e xposure the SEP was 30 mm Hg above that of the control level (P < .001) and was accompanied by a 25% increase in whole blood viscosity (P < .05). At t he end of 8 weeks of cold exposure the plasma volume was 56.8 +/- 9.51 mL/k g and the whole blood viscosity was 8.0 +/- 1.79 cps at the 22.5 per sec sh ear rate. During the 5 weeks of rewarming the elevation of SEP and increase d whole blood viscosity persisted, whereas the increased daily water consum ption and expanded plasma volume returned to normal. Therefore, the acclima tion to cold is accompanied by the development of a volume-associated hyper tension, which is sustained after rewarming without volume expansion. (C) 1 999 American Journal of Hypertension, Ltd.