The effect of bathing with artificial sodium sulfate on changes in the systolic blood pressure and the level of atrial natriuretic polypeptide (ANP) in plasma or atrium of normotensive male rats was studied. The following results were obtained:
1) As a result of bathing for 20 minutes at a temperature of 37°C, the systolic blood pressure lowered and the plasma ANP level decreased. The blood pressure lowered most clearly after artificial sodium sulfate bathing at a prescribed concentration (p<0.5), while the plasma ANP level decreased significantly after plain water bathing (p<0.01).
2) The atrial ANP level showed no significant change. Presumably the reason was that the quantity of atrial ANP was so large that it was not affected by fluctuations in the peripheral ANP level.
3) The temperature and duration of bathing, the concentration of bath salts, and other factors might also influence the plasma ANP level.
These results suggest that the artificial sodium sulfate bathing lowers the blood pressure by preventing heat radiation from the skin and by delicate regulatory mechanisms on ANP secretion.

The effects of bathing with artificial sodium sulfate on the systolic blood pressure and the level of atrial natriuretic peptide (ANP) in plasma and or in atrium of spontaneously hypertensive rats (SHR) were studied. The following results were obtained:
1) As a result of bathing for 20 minutes at a temperature of 37°C, the systolic blood pressure lowered and the plasma ANP level increased. The blood pressure lowered with increasing concentration of sodium sulfate (p<0.01).
2) The plasma ANP level in a standing position for 20 minutes decreased than in a normal position.
3) The plasma ANP level in SHR was higher and increased more clearly by bathing, compared to the previous results in normotensive rats (WKA). The blood pressure lowered far more in SHR than in WKA.
4) The atrial ANP level was not significantly influenced by bathing nor by changing the posture.
These results indicate that the artificial sodium sulfate bathing has more potent hypotensive effect than plain water bathing probably due to prevent heat radiation, and affects the blood pressure and the plasma ANP more significantly in SHR than in WKA. In addition, the effects of mild bathing to cardiovascular and neurohumoral systems may modulate directly or indirectly the ANP secretion.