To find the correlation between the thermal action of hot bathing and the induction of heat-shock proteins (HSP), spontaneously hypertensive rats (SHRs) and normal Wistar rats were subjected to bathing experiments. Tests were also conducted to determine whether two kinds of HSP molecules, HSP 70 and HSP 90, were induced in the brain, liver, and kidneys, and inductive specificities were quantitatively investigated in SHRs.
Both SHRs and normal rats of the hot-spring bathing group showed more potent induction of HSP 70 and HSP 90 at ages of 10 weeks and 26 weeks than the values in those of the plain-water bathing group.
Among SHRs, HSP 70 and HSP 90 decreased in the brain and liver at the age of 26 weeks as compared with those at the age of 10 weeks (with HSP 70 in the brain reduced to half). HSP 70 increased in the kidneys, with HSP 90 hardly detectable. Among normal rats, HSP 70 and HSP 90 decreased in the brain, liver, and kidneys, but the rate of decrease was not so remarkable as in SHRs.
The results suggest that the inhibitory effects of hot-spring bathing on blood pressure of SHRs are closely related to the decrease in the rate of induction of HSPs.