To find the effects of habitual hot-spring bathing from a young age on the blood pressure of adults, the effects of hot-spring bathing on lowering blood pressure and serum lipoperoxides were investigated using spontaneously hypertensive rats (SHR). Male SHRs, six week old, were subjected to hot bathing at 40°C for 10min per day for 14 weeks continuously.
1) Hot bathing tended to suppress blood pressure. For hot-spring bathing, blood pressure was maintained within 100 to 120mmHg until the end of the bathing experiment. Furthermore, these controlled values of blood pressure were maintained for more than 5 weeks after cessation of the experiment. For plain-water bathing, blood pressure increased gradually, but then was maintained within 100 to 145mmHg until the end of the experiment. These values were maintained for 4 weeks after cessation of the bathing experiment. In those SHRs that were not subjected to bathing, blood pressure was 100mmHg at the age of 6 weeks, 150mmHg at the age of 13 weeks, 160mmHg at the age of 19 weeks, and 170mmHg at the age of 24 weeks. Accordingly, it was found that hot-spring bathing is more effective than plain-water ordinary bathing in suppressing blood pressure.
2) The serum lipoperoxide values decreased during the 12th week of the bathing experiment. These values remained at a significantly low level until the end of the 6th week after cessation of the bathing experiment. This finding seems to suggest that habitual bathing from a young age may slow down the aging process.
3) It was shown that the concentrations of catecholamines in blood were lower in both the hot-spring bathing group and the plain-water bathing group than those in the non-bathing group. This may indicate that controlled secretion of catecholamines is related to the relaxation induced by bathing.
4) The rate of weight increase was significantly lower in the groups of SHRs subjected to hot-spring bathing and plain-water bathing from a young age than in the non-bathing group.

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.

To find the correlation between the inhibitory effects of hot-spring water on blood-pressure and its chemical composition, the effects of artificial spa bathing on lowering blood pressure were compared with those of hot-spring bathing on spontaneously hypertensive rats (SHR). Further, the induction of heat-shock proteins (HSP) in rat organs was quantitatively examined in order to clarify the mechanism of its action. Artificial spa (Na₂SO₄-Na₂HCO₃) bathing showed almost the same inhibitory effects on blood pressure as those of hot-spring bathing.
There was no significant difference in the catecholamine value in blood between both types of spa bathing, nor was there any difference from the values of the control group.
It was found that HSP molecules were induced in the brain, liver, and kidneys not only by hot-spring bathing but also by artificial spa bathing, with different inductive profiles from one organ to another.