FIBRINOGEN CLEARANCE FROM THE PULMONARY INTERSTITIUM

Abstract

Previous experiments demonstrated that ¹²⁵ I-human
fibrinogen ( 125-RIF) instilled into the distal airway
of the right lower lobe in intact dogs passed through
the microairway into the interstitium. This report
analyzed the subsequent interstitial clearance of
this fibrinogen by analyzing plasma and lymph
samples for 125 I activity. This activity was separated

into clottable, and trichloroacetic acid (TCA) insoluble
and soluble components. Clottable and
TCA-in soluble 125-RrF in the same ratio appeared
in lymph from the right lymphatic duct (RO) and
thoracic duct (TO). From standard mixing equations
we calculate that 1.4 times as much lymph from
the right lower lobe flows into the TO as into the
RD. With one exception, clottable 125-RIF appeared
in plasma only in the absence of an RO; this suggested
the presence of accessory lymphatico-venous
communications rather than back flux of 125-RlF
at the capillary wall. By injecting 131 I-human fibrinogen

intravenously, we observed a small reduction
in clottability (maximum of 10%) in lymph
both from the RD and TO. Equilibration in RO
lymph was only 1/5 as fast as albumin, and from
the measured equilibration rate constant, and the
assumption that interstitial fibrinogen clearance is
entirely convective, we estimate that the pulmonary
interstitial distribution volume for fibrinogen is 70%
that for albumin. Non dialyzable 125-RIF products
generated in the distal airway adhered to intracapillary,
circulating erythrocytes. These products retained
fibrinogen antigenicity, and appeared to be
further degraded in the vascular compartment.