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Atrial natriuretic factor during head-out immersion at night
1Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
The American Journal of Physiology
|February 1, 1988
Summary
Nocturnal inhibition of renal responses to head-out immersion (HOI) is not fully explained by daily variations in atrial natriuretic factor (ANF). ANF levels increased similarly during daytime and nighttime HOI, despite reduced renal function at night.
Area of Science:
- Physiology
- Circadian Rhythms
- Renal Function
Background:
- Head-out immersion (HOI) typically stimulates renal responses, including diuresis.
- Nocturnal attenuation of renal responses to HOI has been observed, but the underlying mechanisms remain unclear.
- Atrial natriuretic factor (ANF) is a key hormone regulating renal function and fluid balance.
Purpose of the Study:
- To investigate whether circadian variations in atrial natriuretic factor (ANF) response mediate the reduced renal function during nocturnal head-out immersion (HOI).
- To compare plasma ANF levels and renal responses to HOI during daytime and nighttime conditions.
Main Methods:
- Six healthy male subjects underwent 3-hour head-out immersion in water (34.5°C) during both daytime (1000-1300) and nighttime (2400-0300) periods.
- Plasma atrial natriuretic factor (ANF) levels and hematocrit were measured during control periods and at intervals during and after HOI.
- Renal responses, particularly diuresis, and plasma renin activity were assessed.
Main Results:
- Renal responses, especially diuresis, were significantly attenuated during nighttime HOI compared to daytime HOI.
- Plasma ANF levels showed a similar twofold increase within one hour of HOI and remained elevated throughout the immersion period, irrespective of the time of day.
- Plasma renin activity decreased to similar low levels during HOI at both day and night.
- Hematocrit changes indicated a transient plasma volume expansion during HOI, with no significant difference between day and night.
Conclusions:
- Circadian variations in the atrial natriuretic factor (ANF) response do not fully account for the nocturnal inhibition of renal responses to head-out immersion (HOI).
- While HOI induces similar ANF release and fluid shifts during day and night, other factors likely contribute to the observed differences in renal function.