QUANTITATIVE APPROACHES TO THE STUDY OF LYMPHATIC CONTRACTILE ACTIVITY IN VITRO AND IN VIVO: POTENTIAL ROLE OF THIS DYNAMIC 'LYMPH PUMP' IN THE RE-EXPANSION OF THE VASCULAR SPACE FOLLOWING HEMORRHAGE

Abstract

Few investigators have considered a
dynamic role for the lymphatic vessel in
regulating the movement of fluid and protein
from the interstitium back to the bloodstream.
This view is based on the assumption that lymphatics
are passive conduits and that
hydrostatic pressure gradients and external compression
forces acting on the vessels are primarily
responsible for the movement of lymph.
However, it is becoming increasingly evident
that the intrinsic contractile capabilities of lymphatic
vessels provide a major part of the propulsive
force. Lymphatics have noradrenergic
innervation and respond to a variety of
humoral factors and inflammatory mediators
suggesting that the pumping activity is centrally
regulated and in addition, may respond to local
factors. In this article, we will discuss what is
known of the regulation of this 'lymph pump'.
Techniques that permit analysis of contractile
activity and fluid pumping in vitro and in
vivo will be reviewed. Of particular interest is
a sheep model that allows the quantitation of
pumping activity in vivo without the complication
of variable lymph inputs. While there is
little information available at this time concerning
the potential role of the 'lymph pump' in
pathophysiological states, some preliminary experiments
from our own laboratory suggest that
an independently regulated 'lymph pump' may
play an important role in hemorrhagic shock.