Interstitial Exclusion of Albumin in Rabbit Lung Measured with the Continuous Infusion Method in Combination with the Wick Technique

Abstract

Objective:To determine albumin exclusion from the pulmonary perivascular interstitium by using the continuous infusion methods coupled with direct samples of pulmonary interstitial fluid via the wick technique. Methods:To evaluate extracellular albumin distribution volume, radioactive (¹²⁵I) rabbit serum albumin (RSA) was delivered intravenously until reaching a steady-state tissue concentration. In anesthetized rabbits with ligated kidney pedicles, extracellular (V_x) and intravascular (V_v) fluid volumes were measured as the distribution volumes of ⁵¹Cr-ethylenediaminetetraacetic acid and ¹³¹I-RSA, respectively. Post mortem, lung samples and interstitial fluid collected via implanted wicks were assayed for isotope activity. The extravascular wick fluid equivalent albumin distribution volume (V_a,w) was calculated assuming equal concentrations of ¹²⁵I-RSA in interstitial and wick fluid. Results:The mean (±SE) V_x, V_v, and interstitial fluid volumes (V_i= V_x− V_v) were 1896 ± 61 (n= 8), 556.8 ± 19, and 1329 ± 73 µL/g of blood-free dry lung tissue weight, respectively. The mean albumin-excluded volume (V_e,a= V_i− V_a,w) and the excluded fraction (V_e,a/V_i) were 875.8 µL/g ± 58 and 0.66 ± 0.05, respectively. Conclusions:At variance with previous indirect reports, the present data indicate that normal pulmonary parenchyma displays a tight fibrous structure that is highly restrictive with respect to plasma protein distribution. Microcirculation(2003) 10,153–165. doi:10.1038/sj.mn.7800180

• pulmonary interstitium
• interstitial matrix
• wick technique