Hypertension during chronic exposure to cold: comparison between Sprague-Dawley and Long-Evans strains

It is now well established that chronic exposure of rats to cold (5-6 degrees C) induces an elevation of systolic, diastolic, and mean blood pressures and cardiac hypertrophy within 3 weeks. Since rats of the Long-Evans (LE) strain are known to be resistant to the induction of deoxycorticosterone salt induced hypertension, their cardiovascular responses to chronic exposure to cold were compared with those of rats of the Sprague-Dawley (SD) strain. The results of these studies revealed clear differences between the LE and SD strains of rats. Thus, rats of the SD strain had a significant elevation in their blood pressure; a significantly increased urinary output of norepinephrine and epinephrine; a significantly greater dipsogenic responsiveness to acute administration of angiotensin II, and significant increases in weights of the heart, kidneys, adrenals, and brown adipose tissue compared with their warm-adapted controls. All of these changes are characteristic of rats acclimated to cold. In contrast, rats of the LE strain appear to be less responsive to cold in that blood pressure failed to rise as sharply and to attain as high a level. Furthermore, urinary outputs of norepinephrine and epinephrine were significantly lower in cold-treated rats of the LE strain compared with cold-treated rats of the SD strain, but dipsogenic responsiveness to angiotensin II was unchanged. Although increases in the weight of the previously mentioned organs were also observed in cold-treated rats of the LE strain compared with their warm-adapted controls, weights of the heart and interscapular brown adipose tissue of both groups were significantly less than those of counterparts of the SD strain.(ABSTRACT TRUNCATED AT 250 WORDS)