AJP - Renal Physiology, Vol 261, Issue 5 849-F857, Copyright © 1991 by American Physiological Society
Changes in cytochrome oxidation in outer and inner stripes of outer medulla
J. L. Atkins and S. P. Lankford
Department of Nephrology, Walter Reed Army Institute of Research, Washington, District of Columbia 20307-5100.
To examine regional cytochrome oxidation in the outer medulla, we developed
fiber optic probes that allowed us to obtain localized reflectance
measurements from the outer and inner stripes of the outer medulla. We
measured directional changes in cytochrome oxidation in these two regions.
In the outer stripe furosemide surprisingly caused a significant decrease
in cytochrome oxidation. The decrease occurred concomitantly with a fall in
outer medullary blood flow as measured by laser-Doppler flowmetry.
Saralasin, an antagonist of angiotensin II caused a significant increase in
cytochrome oxidation in the outer stripe. In the inner stripe furosemide
tended to increase cytochrome oxidation, and saralasin had no effect. These
results indicate that the two regions of the outer medulla may be affected
differently by the same agent. They suggest that cytochrome oxidation in
the outer stripe is predominantly influenced by outer medullary blood flow,
whereas the inner stripe is predominantly influenced by the rate of oxygen
consumption. The advantages and limitations of this methodology are
discussed.
