AJP - Heart and Circulatory Physiology, Vol 237, Issue 1 99-103, Copyright © 1979 by American Physiological Society
Resistance and volume changes caused by nitroprusside in the dog
S. A. Rubin, G. Misbach, J. Lekven, W. W. Parmley and J. V. Tyberg
Changes in vascular volume caused by a pharmacologic agent are frequently
inferred rather than directly measured. We investigated the effects of
nitroprusside in 8 dogs divided into 2 groups: control and splenectomized.
We anesthetized the dogs using pentobarbital, and surgically prepared a
veno-right atrial bypass preparation whose controlled cardiac output and
external reservoir allowed measurement of both changes in vascular
resistance and changes in vascular volume. In both groups, blood pressure
(mean +/- SD) decreased at each successive level of nitroprusside: 114 +/-
24 mmHg (base line), 101 +/- 19 mmHg (45 microgram/min), 90 +/- 16 mmHg (90
microgram/min), 81 +/- 17 mmHg (180 microgram/min), 68 +/- 18 mmHg (360
microgram/min). Nitroprusside caused a large and similar decrease in
vascular resistance in both groups. In the control group, vascular volume
increased above base line 5.5 +/- 2.7, 8.3 +/- 3.2, 11.6 +/- 2.9, and 14.7
+/- 3.5 ml/kg at each successive level of nitroprusside infusion, whereas
in the splenectomized group vascular volume increased above base line 0.9
+/- 0.3, 2.5 +/- 1.0, 3.3 +/- 1.1, and 4.0 +/- 1.3 ml/kg at each successive
level of nitroprusside infusion, but increased significantly less than the
control group. We concluded that nitroprusside decreases vascular
resistance and increases vascular volume and that the spleen is the major
site of changes in vascular volume caused by nitroprusside.
