C. Risoe et al., EFFECT OF CAROTID-SINUS BARORECEPTOR REFLEX ON HEPATIC AND SPLENIC VASCULAR CAPACITANCE IN VAGOTOMIZED DOGS, The American journal of physiology, 266(4), 1994, pp. 80001528-80001533
Mechanisms of how baroreflex activation changes splanchnic vascular vo
lumes were studied in eight vagotomized dogs, anesthetized by chloralo
se/urethan. Hepatic and splenic vascular volume changes were determine
d from organ dimensions by sonomicrometry. Pulsatile carotid sinus pre
ssure (CSP) in isolated and separately perfused carotid sinuses was ch
anged among 200, 120, and 40 mmHg. Lowering CSP from 120 to 40 mmHg si
gnificantly decreased both hepatic and splenic vascular volume (at sim
ilar portal pressure) by 1.9 +/- 0.5 and 1.8 +/- 0.6 ml/kg body wt, re
spectively. Increasing CSP from 120 to 200 mmHg tended to increase reg
ional vascular volumes (P = NS). The combined volume change of liver a
nd spleen between CSP 40 and 200 mmHg was 4.2 +/- 0.6 ml/kg body wt (P
< 0.001). Pressure-volume (dimension) curves at high, low, and baseli
ne CSP were determined to separate active and passive mechanisms of va
scular volume changes. Changes in CSP did not change regional vascular
compliance. Low CSP significantly decreased unstressed liver and unst
ressed splenic volume by 3.3 +/- 0.9 and 1.9 +/- 0.5 ml/kg body wt, re
spectively. These results indicate that liver and spleen both contribu
te to blood volume mobilization by vasoconstriction during low CSP and
that the carotid sinus baroreceptor reflex modulates hepatic and sple
nic vascular capacitance by changing unstressed volume rather than by
changing vascular compliance.