Hg. Bohlen et Jm. Lash, RESTING OXYGENATION OF RAT AND RABBIT INTESTINE - ARTERIOLAR AND CAPILLARY CONTRIBUTIONS, American journal of physiology. Heart and circulatory physiology, 38(4), 1995, pp. 1342-1348
Counter-current exchange of oxygen may occur between inflow and outflo
w microvessels of the small intestine and greatly influence the domina
nt sites of tissue oxygenation. To determine the location and magnitud
e of potential exchange, percent saturation of hemoglobin with oxygen
(%S-Hb) was measured in microvessels throughout the intestine of rats
and rabbits. Oxygen losses from systemic arterial blood through large
and intermediate arterioles (second order, 2A) was 5-7%S-Hb in both sp
ecies, and there was no evidence of an increase in percent saturation
along intermediate and large venules. A larger loss of oxygen from art
erioles and an increase in venous saturation would be evident if signi
ficant arteriolar to venular counter-current exchange of oxygen occurr
ed in the submucosa. From 2A to the villus tip, arteriolar saturation
decreased similar to 10%S-Hb in rabbits and similar to 15%S-Hb in rats
; the villus tip percent saturation was 72.9 +/- 39%S-Hb in rabbits an
d 69.9 +/- 2.9%S-Hb in rats. An additional decrease of 5%S-Hb in rabbi
ts and 15%S-Hb in rats occurred across the villus capillaries and smal
lest venules. Although the total reduction in percent saturation acros
s the villi was different between the two species, 70-90% of the total
arteriovenous oxygen losses occurred in the capillaries and small art
erioles of the villi. We found no evidence of counter-current exchange
of oxygen in villi or any other vascular region. Rather, as appears t
o occur in most organs, small arterioles in conjunction with capillari
es dominate resting oxygen exchange to tissue.