Effects of Chronic Heat or Cold Exposure on Growth and Blood Pressure in Rats

We studied the effects of various environmental temperatures on growth and blood pressure in rats. Spontaneously hypertensive rats (SHR) and their mother strain, normotensive Wistar-Kyoto rats (WKY) were used as the experimental animal. Rats of the two strains, SHR and WKY of 1 month old were divided into three groups randomly and they were housed in three rooms, of which temperatures were controlled at a constant, 30℃ (H-group), 22-24℃ (N-group) and 10℃ (C-group), respectively. Effects of environmental temperature on body weight gain were studied. Growth retardation was observed in the H-group of both strains. Maximal body weight gains were higher and reduced more quickly in SHR compared to those in WKY. In both SHR and WKY, at approximately 4 months old, the ratio of the tail to body surface areas was in the order of H-group>N-group>C-group in both strains. Systolic blood pressure (BP) was measured by the tail cuff method at approximately 4 months old. In WKY, BP in the C-group was significantly higher than that in H-group. In SHR, the BPs of the three groups were high compared to those in WKY groups, to which rats were exposed since 1 month old. And the BPs of C-group and H-group were significantly high compared to that in N-group. These facts indicate that effects of environmental temperature, to which rats were exposed since 1 month old, on growth were similar in WKY and SHR, and that the effects of the environmental temperature on systemic BP are clear in normotensive WKY, whereas in SHR, genetic expression of the hypertensive phenotype is consistent at various environmental temperatures