Excessive erythrocytosis does not elevate capillary oxygen delivery in subcutaneous mouse tissue.
OBJECTIVE
Acclimatization to reduced environmental oxygen includes erythropoietin-regulated increase in erythrocytes enhancing the blood's oxygen content. However, increased hematocrit levels result in elevated blood viscosity that might impair microcirculation and tissue oxygenation. To assess this oxygen supply to the skin, the authors used erythropoietin overexpressing transgenic mice (tg6) that develop excessive erythrocytosis in an oxygen-independent manner. These animals have been previously reported to elevate their blood viscosity 4-fold.


METHODS
The partial oxygen pressure (pO2) distribution was evaluated in microvessels as well as in subcutaneous interstitial tissue within a dorsal skinfold chamber of resting conscious mice using automated phosphorescence quenching.


RESULTS
Compared to wildtype (wt) animals, transgenic blood viscosity increased 4-fold but microvessel diameter was not altered. Despite sharing similar blood pO2 as the wt siblings, tg6 animals nearly doubled their oxygen content. Moreover, tg6 erythrocytes reduced hemoglobin's oxygen affinity by decreased 2,3-DPG levels and an increased Hill number. Transgenic arterioles and venules showed increased pO2 compared to wt controls whereas capillary and tissue pO2 were not altered.


CONCLUSIONS
Excessive erythrocytosis does not elevate capillary oxygen delivery.
Frietsch
Thomas
T
Department of Anesthesiology and Critical Care Medicine, Medical Faculty Mannheim of the University of Heidelberg, Germany. bv3@ix.urz.uni-heidelberg.de
Gassmann
Max
M
Groth
Gesine
G
Waschke
Klaus F
KF
Vogel
Johannes
J
Cabrales
Pedro
P
Vajkoczi
Peter
P
Dorn-Beineke
Alexandra
A
Intaglietta
Marcos
M
Kerger
Heinz
H
D019794:2,3-Diphosphoglycerate / Q000378:metabolism; D000818:Animals; D030801:Animals, Genetically Modified; D001809:Blood Viscosity / Q000502:physiology; D002196:Capillaries / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism; D004921:Erythropoietin / Q000235:genetics; D005260:Female; D006400:Hematocrit; D006801:Humans; D008297:Male; D051379:Mice; D010100:Oxygen / Q000097:blood*; D010108:Oxyhemoglobins / Q000378:metabolism; D010313:Partial Pressure; D011086:Polycythemia / Q000378:metabolism*; D040521:Subcutaneous Tissue / Q000098:blood supply* / Q000378:metabolism*
D010108:Oxyhemoglobins; D004921:Erythropoietin; D019794:2,3-Diphosphoglycerate; D010100:Oxygen