Effect of histamine on equivalent pore radius in capillaries of isolated dog hindlimb

Abstract

Measurements were made of filtration coefficients ( L p ), area per unit path length ( A Δx ) and of equivalent pore radius ( R p ) in the control state and during continuous intraarterial infusion of histamine (20–60 μg/min per kg limb weight) in the isolated dog hindlimb. The osmotic transient procedure was utilized with lipid-insoluble molecules: urea, glucose, sucrose, raffinose, inulin and Dextran 10 (Pharmacia), employed to produce transient osmotic-pressure effects. The net flux of these substances across the capillary membrane was determined from the arterial-venous concentration difference by chemical analysis. Independent of the absolute value of the reflection coefficient (σ), the A s Δx for diffusion of all substances but Dextran 10 was increased during histamine infusion. R p calculated from the theory of restricted diffusion yielded values of 39 Ångstroms (Å) for control and 38 Å during histamine infusion. Combination of hydrodynamic data ( L p ) with diffusion data A w Δx yielded values for R p of 31 Å for control and 29 Å for histamine. Measurements of plasma-protein osmotic pressure, tissue-protein osmotic pressure, tissue hydrostatic pressure and capillary hydrostatic pressure support the conclusion that histamine (20–60 μg/min per kg limb weight) when administered intraarterially does not affect capillary-membrane porosity. The transient increase in fluid movement across the capillary produced by histamine could result from a change in capillary surface area, an increase in the number of pores per unit surface area, or both. Whatever the mechanism, the increase in fluid movement was not persistent in this preparation and L p reverted to control value 10–20 min after beginning histamine infusion even though the agent continued to be infused.