Body fluid distribution in rats with cold-induced hypertension

The purpose of this experiment was to determine body fluid distribution dur ing chronic cold exposure and to further understand the mechanism of cold-i nduced hypertension. Blood pressures, hematocrit, and the plasma, blood, an d extracellular fluid volumes were measured in rats at intervals of 1, 3, a nd 5 weeks after exposure to cold (5 degrees C). Resting systolic, diastoli c, and mean blood pressures measured by direct arterial cannula were signif icantly elevated in a time-dependent manner over the duration of cold expos ure. The increase in diastolic blood pressure, which reflects the periphera l vascular resistance, exceeded that of systolic blood pressure after both 3 and 5 weeks of exposure to cold. Pulse pressure was significantly decreas ed by 3 and 5 weeks of cold exposure. The plasma, blood, and extracellular fluid volumes were significantly increased after both 1 and 3 weeks of expo sure to cold, but had returned to control levels by 5 weeks of cold exposur e. Cold exposure, however, did not affect the hematocrit. The 2-h water int ake after the cold-exposed rats were returned to warm (25 degrees C) (therm ogenic drinking) was significantly increased compared to that of warm-accli mated rats during the first, third, and fifth week of exposure to cold. The present results suggest that the development of cold-induced hypertension is associated with blood volume expansion, and that the elevated blood pres sure is maintained by increased peripheral vascular resistance without bloo d volume expansion. The results also imply that exposure to cold induces a dehydration in rats. (C) 1999 Elsevier Science Inc.