AJP - Heart and Circulatory Physiology, Vol 235, Issue 6 670-H676, Copyright © 1978 by American Physiological Society
Cardiac output, GFR, and renal excretion rates during maintained volume load in rats
U. Ackermann
The correlation among cardiac output (CO), glomerular filtration rate
(GFR), fractional tubular sodium rejection (TFRNa), and renal excretion
rates of water and salt was investigated during ischemic blood volume
expansion in rats. Initially circulating blood volume was equilibrated
isovolemically with a reservoir volume of 6% albumin solution equal to
one-third the estimated blood volume. Later the equilibrated reservoir
contents were infused intravenously. CO was measured by thermodilution, GFR
by inulin clearance. Significant linear correlations existed between GFR
and the rates of urine flow (r = 0.90), sodium excretion (r = 0.75) and
potassium excretion (r = 0.76) that prevailed 5--10 min after a given GFR
change. The increased GFR was highly correlated with CO (r = 0.94),
probably correlated with mean central venous pressure (r = 0.45), but not
correlated with mean abdominal aortic blood pressure. The correlation
between CO and time-delayed (5--10 min) TRFNa was also highly significant
(r = 0.98). The saluresis appears to have been caused initially by
increased tubular load and subsequently by decreased absolute tubular
reabsorption.
