Abstract
We hypothesized that ultrafiltrate crossing the luminal endothelial glycocalyx through infrequent discontinuities (gaps) in the tight junction (TJ) strand of endothelial clefts reduces albumin diffusive flux from tissue into the 'protected region' of the cleft on the luminal side of the TJ. Thus, the effective oncotic pressure difference (σΔπ) opposing filtration is greater than that measured between lumen and interstitial fluid. To test this we measured σΔπi across rat mesenteric microvessels perfused with albumin (50 mg ml-1) with and without interstitial albumin at the same concentration within a few micrometres of the endothelium as demonstrated by confocal microscopy. We found σΔπ was near 70% of luminal oncotic pressure when the tissue concentration equalled that in the lumen. We determined size and frequency of TJ strand gaps in endothelial clefts using serial section electron microscopy. We found nine gaps in the reconstructed clefts having mean spacing of 3.59 μm and mean length of 315 nm. The mean depth of the TJ strand near gaps was 67 nm and the mean cleft path length from lumen to interstitium was 411 nm. With these parameters our three-dimensional hydrodynamic model confirmed that fluid velocity was high at gaps in the TJ strand so that even at relatively low hydraulic pressures the albumin concentration on the tissue side of the glycocalyx was significantly lower than in the interstitium. The results conform to the hypothesis that colloid osmotic forces opposing filtration across non-fenestrated continuous capillaries are developed across the endothelial glycocalyx and that the oncotic pressure of interstitial fluid does not directly determine fluid balance across microvascular endothelium.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 889-907 |
| Number of pages | 19 |
| Journal | Journal of Physiology |
| Volume | 557 |
| Issue number | 3 |
| DOIs | |
| State | Published - Jun 15 2004 |
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ASJC Scopus subject areas
- Physiology
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Oncotic pressures opposing filtration across non-fenestrated rat microvessels. / Adamson, R. H.; Lenz, J. F.; Zhang, X.; Adamson, G. N.; Weinbaum, S.; Curry, F. E.
In: Journal of Physiology, Vol. 557, No. 3, 15.06.2004, p. 889-907.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Oncotic pressures opposing filtration across non-fenestrated rat microvessels
AU - Adamson, R. H.
AU - Lenz, J. F.
AU - Zhang, X.
AU - Adamson, G. N.
AU - Weinbaum, S.
AU - Curry, F. E.
PY - 2004/6/15
Y1 - 2004/6/15
N2 - We hypothesized that ultrafiltrate crossing the luminal endothelial glycocalyx through infrequent discontinuities (gaps) in the tight junction (TJ) strand of endothelial clefts reduces albumin diffusive flux from tissue into the 'protected region' of the cleft on the luminal side of the TJ. Thus, the effective oncotic pressure difference (σΔπ) opposing filtration is greater than that measured between lumen and interstitial fluid. To test this we measured σΔπi across rat mesenteric microvessels perfused with albumin (50 mg ml-1) with and without interstitial albumin at the same concentration within a few micrometres of the endothelium as demonstrated by confocal microscopy. We found σΔπ was near 70% of luminal oncotic pressure when the tissue concentration equalled that in the lumen. We determined size and frequency of TJ strand gaps in endothelial clefts using serial section electron microscopy. We found nine gaps in the reconstructed clefts having mean spacing of 3.59 μm and mean length of 315 nm. The mean depth of the TJ strand near gaps was 67 nm and the mean cleft path length from lumen to interstitium was 411 nm. With these parameters our three-dimensional hydrodynamic model confirmed that fluid velocity was high at gaps in the TJ strand so that even at relatively low hydraulic pressures the albumin concentration on the tissue side of the glycocalyx was significantly lower than in the interstitium. The results conform to the hypothesis that colloid osmotic forces opposing filtration across non-fenestrated continuous capillaries are developed across the endothelial glycocalyx and that the oncotic pressure of interstitial fluid does not directly determine fluid balance across microvascular endothelium.
AB - We hypothesized that ultrafiltrate crossing the luminal endothelial glycocalyx through infrequent discontinuities (gaps) in the tight junction (TJ) strand of endothelial clefts reduces albumin diffusive flux from tissue into the 'protected region' of the cleft on the luminal side of the TJ. Thus, the effective oncotic pressure difference (σΔπ) opposing filtration is greater than that measured between lumen and interstitial fluid. To test this we measured σΔπi across rat mesenteric microvessels perfused with albumin (50 mg ml-1) with and without interstitial albumin at the same concentration within a few micrometres of the endothelium as demonstrated by confocal microscopy. We found σΔπ was near 70% of luminal oncotic pressure when the tissue concentration equalled that in the lumen. We determined size and frequency of TJ strand gaps in endothelial clefts using serial section electron microscopy. We found nine gaps in the reconstructed clefts having mean spacing of 3.59 μm and mean length of 315 nm. The mean depth of the TJ strand near gaps was 67 nm and the mean cleft path length from lumen to interstitium was 411 nm. With these parameters our three-dimensional hydrodynamic model confirmed that fluid velocity was high at gaps in the TJ strand so that even at relatively low hydraulic pressures the albumin concentration on the tissue side of the glycocalyx was significantly lower than in the interstitium. The results conform to the hypothesis that colloid osmotic forces opposing filtration across non-fenestrated continuous capillaries are developed across the endothelial glycocalyx and that the oncotic pressure of interstitial fluid does not directly determine fluid balance across microvascular endothelium.
UR - http://www.scopus.com/inward/record.url?scp=3242688889&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=3242688889&partnerID=8YFLogxK
U2 - 10.1113/jphysiol.2003.058255
DO - 10.1113/jphysiol.2003.058255
M3 - Article
C2 - 15073281
AN - SCOPUS:3242688889
VL - 557
SP - 889
EP - 907
JO - Journal of Physiology
JF - Journal of Physiology
SN - 0022-3751
IS - 3
ER -