AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 2 349-R357, Copyright © 1995 by American Physiological Society
Adaptive resetting of the volume control of vasopressin secretion during sustained hypovolemia
Y. Iwasaki, M. B. Gaskill and G. L. Robertson
Department of Medicine, University of Chicago Medical School, Illinois 60637.
To determine the effect of sustained hypovolemia on vasopressin secretion,
we studied rats after 1-32 h of diuretic therapy. We found that an
injection of furosemide (10 mg/kg) produced a transient marked increase in
urine output, a moderate 7-10% reduction in blood volume, and a three- to
fourfold rise in plasma vasopressin from 1.6 +/- 0.2 to 5.6 +/- 1.0 pmol/l.
When the hypovolemia was maintained by repeated injections of the diuretic,
plasma vasopressin remained elevated for > or = 8 h but returned almost
to normal by 32 h, even though plasma electrolytes, blood pressure,
hematocrit, and the other measures of hypovolemia were unchanged. At this
time, pituitary vasopressin was undiminished, and plasma vasopressin rose
normally or even supranormally when an acute hypovolemic or osmotic
stimulus (intraperitoneal polyethylene glycol or hypertonic saline) was
superimposed. However, the lines describing the relationship of log plasma
vasopressin to plasma volume and plasma sodium in the rats treated with
furosemide for 32 h lay to the left of the same relationships in the rats
treated for 8 h or the sham-treated controls. We conclude that, in rats,
the vasopressin response to sustained hypovolemia persists for > or = 8
h but is markedly diminished by 32 h. The decline in plasma vasopressin
during this interval appears to be due to adaptive resetting of the volume
control mechanism.
