Control of right atrial pressure at constant cardiac output suppresses volume natriuresis in anesthetized rats

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Abstract
The blood volume of anesthetized rats was expanded acutely by 33% with donor blood while a caval snare was gradually tightened so that right atrial pressure (RAP) was prevented from rising (n = 6). In control experiments (n = 5) an aortic snare was used to hold mean arterial blood pressure near the values found in the experimental series. RAP was allowed to change freely and increased by 1.6 .+-. 0.4 mm Hg (1 mm Hg = 133.322 Pa [pascals]) during volume expansion. When the 2 groups were compared, there were no significant differences between their mean arterial blood pressures (near 110 mm Hg) or in their cardiac outputs (near 0.25 ml .cntdot. min .cntdot. g body wt-1). There were significant differences between their renal responses to the volume load. When RAP was free to change, the rate of volume excretion (.ovrhdot.V) increased to 30 .+-. 15 (SEM [standared error of the mean]) .mu.l .cntdot. min .cntdot. g kidney weight-1 (KW) from its control value of 3.49 .+-. 0.31 and the rate of Na secretion (UNa.ovrhdot.V) increased to 3.59 .+-. 0.20 .mu.equiv. .cntdot. min .cntdot. g KW-1 from its preinfusion value of 0.42 .+-. 0.10. When RAP was not allowed to increase during volume loading, .ovrhdot.V and UNa.ovrhdot.V did not change from their respective preinfusion values (2.99 .+-. 0.46 .mu.l .cntdot. min .cntdot. g KW-1 and 0.35 .+-. 0.10 .mu.equiv. .cntdot. min .cntdot. g KW-1). During acute blood volume expansion increased central vascular pressure apparently is a prerequisite for the homeostasis of body water and salt.