Oxygen saturation and ph changes in cremaster microvessels of the
rat.
Kobayashi, Hirosuke, and Naosada Takizawa.
Department of Medicine, and Physiology, Kitasato University School
of Medicine, Kitasato 1-15-1, Sagamihara, Kanagawa 228, Japan
APStracts 2:0460H, 1995.
Recent studies have shown a considerable extent of diffusive oxygen
transfer from pre-capillary vessels, but the occurrence of oxygen
influx into post-capillary vessels (diffusive shunting) is still
controversial. In this study we investigated diffusive shunting
between pre- and post-capillary vessels in muscle tissue and pH
changes in the microvessels in an attempt to determine the
physiological significance of the parallel arrangement of arterial
and venous vessels in tissue oxygenation. We used rat cremaster
muscles, and controlled the breathing of anesthetized rats using
urethane with FIO2 set at 0.3 and 0.12. We employed a non-invasive
spectrophotometric method of measuring pH, using a pH sensitive dye
(1-hydroxypyrene-3,6,8-trisulfonic acid) and the oxygen saturation
level of hemoglobin (SO2) in microvessels from small arteries down to
arterioles, and from venules up to small veins. At FIO2 0.30 pH
significantly decreased from 7.39 0.02 (mean S.D.) to 7.26 0.05 in
pre-capillary vessels and remained close to constant during passage
through post-capillary vessels. At FIO2 0.12 pH decreased from 7.36
0.03 to 7.01 0.06 in pre-capillary vessels and then increased in
post-capillary vessels from 6.75 0.19 to 7.27 0.08. At FIO2 0.30 SO2
decreased from 98.6 5.4 to 64.2 4.5% in pre-capillary vessels and
increased from 62.5 6.5 to 89.4 4.1% in post-capillary vessels. At
FIO2 0.12 SO2 decreased from 47.0 5.5 to 25.1 3.8% in pre-capillary
vessels and remained close to constant in post-capillary vessels. In
conclusion, during hyperoxia diffusive shunting of oxygen was
enhanced, and during hypoxia acid was accumulated in peripheral
vessels. It is speculated that acid accumulated due to back-diffusion
of CO2 from venous to arterial microvessels, liberating oxygen bound
to hemoglobin via the Bohr effect. The diffusive shunting of oxygen
and counter-diffusion and accumulation of CO2 may contribute to the
homeostasis of tissue oxygenation levels.
Received 5 June 1995; accepted in final form 26 September 1995.
APS Manuscript Number H514-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95