EFECTS OF ACETYLCHOLINE ON PERIPHERAL VASCULAR PROTEIN PERMEABILITY

Abstract

It is common practice to assume that when a
vasodilator such as acetylcholine (ACh) produces a
decrease in lymph/plasma protein ratio (R) while
lymph flow (L) increases, permeability-surface area
product (PS) and reflection coefficient (a) are unchanged.
However, if PS and a are unaltered by a
stimulus that increases L, then a decreased R can be
associated with an elevated, constant, or reduced a
and PS. To test what the effect of ACh, a "pure
vasodilator," is in the hindquarters of the anesthetized
dog, we infused 127 micrograms ACh min·1 into the abdominal
aorta of 6 female mongrel dogs while collecting
lumbar trunk lymph in order to measure L and
R. a and PS were computed by the method of fluctuations
over 15 min collections. The rise or decrease
in LR was well correlated with L (r=.951) as expected,
but was much less than predicted if a and PS
had been unaltered during ACh infusion. Computations
indicated that a rose with ACh approximately
34% (P = .0007) and PS rose 54% (P = .042)
above control. This can be interpreted as a decrease
in the radial dimension of the protein transport channels
and an increase in the number of such channels
per unit area, with both changes induced either by
altered capillary anatomy or redistribution in a
heteroporous system. Such an analysis seems compatible
with the results of other studies in a variety of
tissues which indicate that ACh tightens membranes
either directly or through an effect mediated by
reduced arterial pressure.