Effect of a Reduction in Sodium Intake on Cold-Induced Elevation of Blood Pressure in the Rat

Abstract

Chronic exposure of rats to cold (5 degrees C) induces hypertension within 3 weeks. The objective of this study was to determine the effect of treatment with graded levels of dietary NaCl on the induction of hypertension during chronic exposure to cold. Four groups of male rats were used. The first, given a commercial sodium-deficient diet containing 0.30% NaCl, served as the warm-adapted control group. The second, third, and fourth groups were given the same diet containing 0.075%, 0.15%, and 0.30% NaCl, respectively. Because cold-exposed rats ingest approximately twice as much food as warm-adapted controls, this represented half, the same, and twice the amount of NaCl ingested by the control group. The latter three groups were placed in cold air (5 degrees C). All cold-treated groups had an elevation of systolic blood pressure that was proportional to the concentration of NaCl in the diet by the seventeenth week of exposure to cold. Cardiac hypertrophy occurred to the same extent in all cold-exposed groups and was thus unaffected by the NaCl content of the diet or by the extent of elevation of blood pressure. Hence, cardiac hypertrophy during chronic exposure to cold is supported by other factors, possibly by the increased concentration of either norepinephrine or triiodothyronine, or both, which occurs characteristically in rats under these conditions. The results of this experiment suggest that the amount of NaCl ingested daily plays a role in the cold-induced elevation of blood pressure observed in rats.

The Relationship between Cold Exposure and Hypertension

“…Many studies about hypertension have been performed [8][9][10][11][12][13][14][15][16] in laboratory animals, but studies about hypertension in cold-exposed workers are very rare.…”

Historic perspectives and recent advances in major animal models of Hypertension1

“…Indeed, plasma renin activity (PRA) is increased during exposure to cold and abolishment of the rise in PRA by renal denervation prevents the development of CIH [32] . Cold-exposed rats had an elevation of blood pressure that was proportional to the concentration of NaCl in the diet [49] , suggesting that CIH is sodium-dependent hypertension.…”

Impact of cold adaptation on cardiac tolerance to ischemia-reperfusion. Role of glucocorticoid and thyroid hormones

“…We have shown that continuous exposure to the cold causes cardiac hypertrophy, the left ventricle mass index was increased by 16% in CCE group. The cold induced hypertrophy of the myocardium has been demonstrated by other authors (Hamilton and Ferguson 1972;Harri et al 1984;van Bergen et al 1992). Apparently this hypertrophy in the heart is the result of an increase in blood pressure.…”

“…The first protocol (protocol 1) included animals with continuous cold exposures (CCE), they resided inside the refrigerator chamber (23 m 3 ) at +4°C two rats in a cage for four weeks (Kvetnansky et al 2012). The second protocol (protocol 2) included rats with long intermittent cold exposures (LICE) which were exposed at +4°C for 8 h daily for 4 weeks (van Bergen et al 1992). The third protocol (protocol 3) included animals which were subjected to brief intermittent cold exposures (BICE), which were in a cold chamber at +4°C for 1.5 h daily for 28 days (4 weeks) (Bozhko and Gorodetskaya 1994).…”

“…The rate of acute myocardial infarction (AMI) among the migrants to the Far North increases dramatically after 7-10 years in the Arctic (Turchinskiy 1979). An unexpected AMI statistic is that 24% of AMI cases in the polar city of Norilsk Russia occur in individuals under 44 years of age (Turchinskiy and Sakharova 1979).…”