AJP - Regulatory, Integrative and Comparative Physiology, Vol 254, Issue 2 235-R241, Copyright © 1988 by American Physiological Society
Atrial natriuretic factor during head-out immersion at night
K. Miki, K. Shiraki, S. Sagawa, A. J. de Bold and S. K. Hong
Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
The present investigation was undertaken to test the hypothesis that a
circadian variation in the atrial natriuretic factor (ANF) response is
responsible for the nocturnal inhibition of renal responses to head-out
immersion (HOI). Plasma ANF responses to a 3-h HOI (water temperature 34.5
+/- 0.5 degrees C) were studied during day (1000-1300) and night
(2400-0300) in six hydropenic male human subjects. In agreement with the
previous observations, the renal responses, especially the diuresis, to HOI
were attenuated at night compared with the day; furthermore, plasma renin
activity decreased to the same low level during HOI at both day and night.
Plasma ANF during time control periods was 30-40 pg/ml without showing any
circadian variation. Moreover, plasma ANF showed a similar twofold increase
within 1 h of HOI and was maintained at this elevated level throughout the
3-h HOI period in both the daytime and the nighttime series. On termination
of HOI, plasma ANF decreased linearly to the pre-HOI level within 1 h.
Hematocrit during time control periods was higher during the day compared
with the night (P less than 0.05). Although HOI appears to induce a
transient increase in plasma volume (as indicated by decreases in
hematocrit) during the 1 h of HOI, the magnitude of the decrease in the
latter parameters was not different between day and night. It is concluded
that nocturnal inhibition of renal responses to HOI cannot be fully
accounted for by circadian differences in the ANF and fluid shift response
to HOI.
