Reversibility of cold-induced hypertension after removal of rats from cold

Abstract

Chronic exposure of rats to cold air induces hypertension, including elevation of blood pressure and cardiac hypertrophy. The present study was designed to assess reversibility of these changes after removal from cold. Five groups of six male rats each were exposed to cold (5 ± 2 °C) for 39 days, while six control rats were maintained at 26 ± 2 °C. Systolic blood pressures of the rats in one of the cold-treated groups, as well as the controls, were measured twice weekly throughout the experiment. Blood pressure of the cold-exposed rats (150 ± 3 mmHg; 1 mmHg = 133.3 Pa) became elevated significantly above that of controls (129 ± 3 mmHg) within 4 weeks. On day 39 of cold exposure, one group (six rats) of the cold-treated rats was sacrificed while still in the cold. The remaining four groups of cold-treated rats were than removed from cold and kept at 26 ± 2 °C. One group of cold-treated rats was sacrificed weekly thereafter. During the last week, the six control rats were also sacrificed. At death, the heart, kidneys, and adrenal glands were removed and weighed. Mean heart weight of the cold-treated group (346 ± 7 mg/100 g body weight), sacrificed prior to removal from cold, was significantly (p < 0.01) greater than that of controls (268 ± 5 mg/100 g body weight). The increased heart weight of the cold-treated group appeared to result mainly from an increase in left ventricular weight. The weights (mg/100 g body weight) of the kidneys and adrenal glands of cold-treated rats, measured prior to removal from cold, were significantly (p < 0.01) greater than those of controls. Two weeks after removal from cold, blood pressure, heart weight, and left ventricular weight decreased from the levels observed prior to removal from cold. However, they were still significantly greater than those of controls through the fourth week after removal from cold. Thus, the hypertension accompanying a 39-day exposure to cold appears to be only partially reversible at 4 weeks after removal from cold.Key words: cold exposure, hypertension, blood pressure, reversibility of hypertension, renal hypertrophy, cardiac hypertrophy.