AJP - Heart and Circulatory Physiology, Vol 257, Issue 4 1049-H1055, Copyright © 1989 by American Physiological Society
Influence of verapamil on total and regional intravascular volume in dogs
B. S. Weinstock, L. Bell and D. L. Rutlen
Cardiology Section, Yale University School of Medicine, New Haven, Connecticut 06510.
Verapamil's influence on intravascular volume (IV) in the total capacitance
circulation was examined in anesthetized dogs after mecamylamine or
baroreceptor denervation. Blood was drained from the venae cavae to an
extracorporeal reservoir and returned to the right atrium at a constant
rate so that IV changes could be measured as reciprocal changes in
reservoir volume. In 10 dogs, verapamil (50 micrograms/min) caused a
decrease in total IV of 74 +/- 12 ml (P less than 0.0005) at 20 min and a
decrease in arterial pressure from 79 +/- 5 to 66 +/- 3 mmHg (P less than
0.0005). After evisceration in nine animals, verapamil caused an
extrasplanchnic (XSPL) IV decrease of 97 +/- 19 ml (P = 0.08). In 11
animals with separate perfusion and drainage of the splanchnic and XSPL
circulations, verapamil caused an XSPL IV decrease of 74 +/- 20 ml (P less
than 0.002) and a splanchnic IV increase of 19 +/- 9 ml (P = 0.06). In four
animals on cardiopulmonary bypass, IV decreased 154 +/- 66 ml (P less than
0.002) during verapamil administration. Thus total IV decreases due to a
decrease in systemic extrasplanchnic volume. Because pressure decreased
while arterial flow and venous outflow pressure were constant, a decrease
in the resistance to blood return to the central circulation mediates the
XSPL volume decrement.
