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

Abstract To investigate the mechanisms of cold-induced hypertension, the systolic blood pressure (SBP) and average daily water consumption were measured weekly in 6-month-old male Wistar rats; they were subsequently acclimated to thermoneutrality (26°C for 7 weeks), to cold temperature (6°C for 9 weeks), and then again reacclimated to 26°C for 5 weeks. Circulating plasma volume and whole blood viscosity were measured in subgroups of rats at the end of acclimation to 26°C after 2 days, after 1, 6, and 8 weeks of cold, and after 2 and 5 weeks of rewarming. The control values obtained at the end of thermoneutral period were: SBP = 130.8 ±18.6 mm Hg, plasma volume = 41.9 ± 4.64 mL/kg, whole body viscosity at shear rate 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 in plasma volume that persisted to a lesser degree throughout the whole period of cold exposure ( P P P