Pulmonary distribution of iodoantipyrine: temperature and lipid solubility effects.

In multiple indicator-dilution studies in rat and dog lungs, we have found that the distribution of iodoantipyrine (IAP) is not limited by the endothelium at a temperature > 7 degrees C but is barrier limited at the epithelium at a temperature < 15 degrees C (permeability coefficient of 6.3 x 10(-5) cm/s at 8 degrees C). IAP extraction from the vascular surface to the tissues is greater than those of antipyrine (AP) and tritiated water (THO). IAP transmittance from the alveolar surface to the vascular compartment is smaller than those of AP and THO: a lung lipid compartment, probably in the lamellar bodies of the type II cells, is more accessible to IAP than to AP or THO because IAP has a higher oil-to-water distribution coefficient. Our mathematical model takes into account these matters and also the low surface density of the type II cells: some of the IAP may bypass the lipid compartment. Lipid may affect the transit of solutes with high oil-to-water distribution coefficients in the lungs and across the alveolar-capillary barrier.

Pulmonary vascular extraction and distribution of antipyrine with alveolar flooding.

Transport characteristics of antipyrine (AP), 22Na+, and tritiated water (THO) were assessed in dog lungs by multiple indicator-dilution experiments in vivo with anesthesia and in isolated perfused preparations before and after alveolar flooding. In controls, outflow patterns of AP and THO were nearly identical. In flooding, AP and THO patterns separated. THO upslopes decreased and mean (t) and modal (tmax) transit times increased as flooding increased; AP initial upslopes remained relatively unchanged but t increased, whereas tmax decreased. Patterns of 22Na+ were unchanged. The results indicate 22Na+ limitation at the endothelium, AP limitation only at the epithelium, and no THO limitation. A mathematical model is based on axial and orthogonal distribution of AP and THO. With alveolar flooding, diffusional distance may be a limiting factor in this distribution.

The diffusional transport of water and small solutes in isolated endothelial cells and erythrocytes.

The diffusional permeability coefficients, PD, for tritiated water (3HHO) 14C-antipyrine (AP) and 14C-iodoantipyrine (IAP) in isolated calf pulmonary artery endothelial cells and dog erythrocytes are measured with the linear diffusion technique at 11.5, 15, 20 and 37 degrees C. The PD values for both cell populations follow the sequence 3HHO > IAP > AP at each of the temperatures. PD for water is higher in the erythrocyte compared to the endothelial cells. The differences in PD for AP and IAP in the erythrocytes and endothelial cells are not dramatic and are similar to the differences seen in comparing permeation of the same solute through bilayers of different composition. A comparison of the values of PD calculated for the endothelial cells with those for isolated capillaries and the structured endothelium in whole lungs validates the use of the isolated cells as models for the endothelial cells in situ. Incubation of the endothelial cells with cis-vaccenic acid or cholesterol produces a reduction in PD for water and antipyrine. These data are analyzed in terms of Stokesian and non-Stokesian diffusion. The interpretation which best accommodates the data is that the phospholipid area of the membrane, rather than the hydrocarbon core, provides the greatest resistance to permeation for these solutes.

Endothelial and epithelial permeabilities to antipyrine in rat and dog lungs.

Temperature effects on the permeabilities of the structured endothelium and epithelium to antipyrine (AP) have been determined with the indicator dilution technique in isolated rat and dog lungs perfused between 38 and 8 degrees C. Permeability coefficients of the endothelium to AP [Pendo(AP)] from the Crone equation are smaller than values for isolated endothelial cells but close to the permeability coefficient of the interstitial epithelial plasmalemma [Pepi(AP)] obtained from physical and mathematical models. In these, tracer water is flow limited at the endothelium and the epithelium at all temperatures; AP is flow limited at the endothelium at T greater than 20 degrees C but barrier limited at the endothelium for T less than 20 degrees C and at the epithelium at all temperatures. At T less than 20 degrees C, log Pendo(AP) decreases regularly with 1/T, with a slope close to that found in cultured bovine pulmonary artery endothelial cells. At 15 degrees C, Pendo(AP) for the endothelial plasmalemma in situ is 30 X 10(-5) cm/s and is 56 X 10(-5) cm/s for the isolated cells in support of transcellular rather than paracellular passage. At T greater than 20 degrees C, log Pepi(AP) in situ decreases slightly with 1/T, with a discontinuity at T = 20 degrees C, and for T less than 20 degrees C, decreases with 1/T with a slope close to that of Pendo(AP). At 15 degrees C, Pepi(AP) is 2.8 X 10(-5) cm/s. The discontinuity may represent a change in the physical state of lipids in the interstitial plasmalemma of the epithelial cells.

The influence of circulatory overload on extraalveolar microvessel endothelium of dog lung in vivo.

In an earlier study from this laboratory, morphometric evaluations of the alveolar capillary endothelium of the lungs of intact dogs were recorded after periods of sustained increases of pulmonary microvascular pressures (D. O. DeFouw, W. O. Cua, and F. P. Chinard, 1983, Microvasc. Res. 25, 56-67). In the present study ultrastructural characteristics of the extraalveolar microvessel endothelium of these dog lungs were evaluated. Small (25- to 50-microns luminal diameter) nonmuscular vessels, which adjoin the alveolar capillaries, and larger (51-200 microns) partially muscular and muscular microvessels were assessed. After increased microvascular filtration, to be expected from the increased hydrostatic pressures, fluid accumulation was found only in the connective tissue sleeves of the larger microvessels. The endothelium of these partially muscular and muscular vessels was markedly affected by fluid distension of the periendothelial interstitium. The endothelial response included the appearance of basal (abluminal) surface invaginations, de novo plasmalemmal vesicle formation, and increased numbers of cytoplasmic vacuoles. The small nonmuscular microvessels lacked both the fluid cuffs and the alterations of endothelial ultrastructure. This latter observation is consistent with the previous report from this laboratory that indicated an absence of both alveolar septal edema and increased capillary endothelial vesicle densities in these lungs (DeFouw et al., 1983). Thus, it seems likely that the conformational changes of the endothelium of the larger microvessels were related to the formation of the periendothelial fluid cuffs. The mechanisms responsible for this endothelial response have not been determined but can be explained on the basis of the testable hypothesis that they are secondary to an increase of tissue pressure associated with accumulation of tissue fluid. These changes may thus represent a secondary structural adaptation to the increased tissue pressures and may serve as a potential vesicular-vacuolar pathway across the endothelium.

The osmotic permeability of isolated calf pulmonary artery endothelial cells.

Osmotic permeability coefficients, PF, for water in isolated calf pulmonary artery endothelial cells determined over the temperature range 41 to 20 degrees C are 311.10(-5) cm.s-1 at 37 degrees C and 159.10(-5) cm.s-1 at 20 degrees C. The value at 37 degrees C is close to that reported earlier for the diffusional permeability coefficient, PD. The PF/PD ratio is 1.0 at 37 degrees C. The PF values are within the range of values extrapolated for filtration permeability in pulmonary endothelium. The temperature dependence expressed as the activation energy is 7.2 kcal.mol-1. The product of hydraulic conductivity, Lp (or PF) and of viscosity changes in water is not constant from 37 to 20 degrees C. These results can be interpreted to indicate a similar pathway for water whether under diffusional or osmotic gradients.

Endothelial extraction of tracer water varies with extravascular water in dog lungs.

In multiple indicator-dilution experiments, transvascular passage of a permeating indicator is conventionally derived from the up-slope separation of the curve of the permeating indicator from that of a vascular reference and is expressed as the extraction (Ec). Extraction may be limited by the barrier (barrier-limited distribution). It may be limited by the volume of distribution accessible to it; in the time domain of an indicator-dilution experiment, the passage to and distribution in the extravascular volume are rapid relative to the velocity of blood in the exchange vessels. We examine here the relations of the extraction of tracer water as tritium oxide (THO) [Ec(THO)] and of the extraction of tracer sodium as 22Na [Ec(22Na)] to extravascular lung water, delta V wev, by adding isotonic fluid to the gas phase of the lungs. The net convective transvascular passage of water is negligible relative to the transendothelial molecular exchange. In 10 experiments in vivo and in 10 experiments in isolated perfused lungs, Ec(THO) increases as delta V wev increases. Ec(22Na) and the permeability-surface area product (PS) for 22Na do not change as delta V wev increases. We conclude that the extraction of THO is determined mainly by the volume accessible to it (flow- or volume-limited distribution) and that the extraction of 22Na is determined mainly by the resistance of the endothelium (barrier-limited distribution). A diffusion limitation in the added alveolar fluid rather than a barrier limitation at the endothelium may moderate Ec(THO).

Water permeability of alveolar macrophages.

The hydraulic conductivity coefficient (Lp) of alveolar macrophages, recovered by lavage from dog lungs, was determined by following volume changes induced by changes of nonpermeating solute concentrations of suspending fluid as a function of time at 20 degrees C. The volume changes were monitored as changes in absorbance of the suspended cells at 600 nm. Cell surface area was calculated from cell volume and diameter. Linear relationships between cell volume and solution osmolality changes were found over the range of 320-520 mosmol/kg; beyond these ranges the macrophages did not respond with swelling or shrinking. Lp and the filtration coefficient (Pf) were calculated from the total volume change over time. At 20 degrees C these were, respectively, 15.7 X 10(-10) cm X cmH2O-1 X s-1 and 217 X 10(-5) cm/s. Comparison of Pf and the diffusional permeability coefficient (Pd) for water of 70 X 10(-5) cm/s, yields a Pf-to-Pd ratio of 3.1. The hypothesis of water passage through aqueous membrane pores is compatible with these data. However, diffusion of water in the glycocalyx of the pericellular domain could be restricted. Pd would then be underestimated, and a falsely high ratio would be calculated. We have no evidence to support this possibility.

Endothelial extraction of tracer water is independent of temperature in dog lungs.

Diffusion and viscosity-dependent flow rates generally decrease with decrease of temperature in biological systems. We have examined the extraction (Ec) of tracer water in isolated dog lungs perfused near 37 degrees C and near 15 degrees C with multiple-indicator dilution experiments. If Ec were barrier limited, Ec should be less at lower temperatures. Two runs at 37 degrees C were followed by two runs at 15 degrees C. Evans blue (T-1824) was used as vascular reference, and tritium oxide (THO) was used as water tracer. Values of Ec were based on the ratio of the areas under the two indicator curves from appearance time to time of peak of T-1824. Values for permeability-surface area (PS) products were calculated from the classical Crone relationship in 14 experiments with a total of 56 runs. Neither Ec nor PS decreased with temperature. Instead, modest but statistically significant increases were found. We conclude that the extraction of tracer water in these preparations is not barrier limited.

Morphometric and physiological studies of alveolar microvessels in dog lungs in vivo after sustained increases in pulmonary microvascular pressures and after sustained decreases in plasma oncotic pressures.

Previous investigations from this laboratory of isolated-perfused dog lungs have shown that volume densities of vesicles in both capillary endothelial and type I epithelial cells are substantially increased after acute, severe edema produced by increasing microvascular pressures (D. O. DeFouw and P. B. Berendsen, 1978, Circ. Res. 43, 72-82) and after decreasing macromolecular concentrations of the perfusate (D. O. DeFouw and P. B. Berendsen, 1979, Microvasc. Res. 17, 90-103). The present study provides morphometric evaluations of alveolar vessel endothelium of the lungs of intact dogs after episodes of sustained increased microvascular pressures and after sustained decreases of plasma oncotic pressures. Endothelial vesicular volume densities did not increase in either case. Fluid accumulation was found in the extraalveolar connective tissue spaces (mainly perivascular); no changes of endothelial or interstitial compartmental thicknesses were observed on either the thin or thick sides of the alveolar septa. Thus, if the increased outward filtration to be expected from the increased hydrostatic or decreased oncotic pressures occurred in the microvasculature, it was moderated by increased hydrostatic and decreased oncotic pressures in the tissues or was accommodated by increased lymph flow rates. Our tentative hypothesis that increased septal interstitial pressure plays a role in initiating vesicle formation in alveolar endothelial cells is consistent with these data if the postulated increases of tissue pressure are less than in the isolated perfused preparations. Our data do not provide support for the concept that endothelial vesicles play a major, early role in the development of pulmonary edema.