AJP - Heart and Circulatory Physiology, Vol 256, Issue 4 1023-H1029, Copyright © 1989 by American Physiological Society
Whole body autoregulation in conscious areflexic rats during hypoxia and hyperoxia
C. Hinojosa-Laborde, A. S. Greene and A. W. Cowley Jr
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226.
We have previously shown whole body autoregulation during normoxia in
conscious areflexic rats in response to an acute increase and decrease in
blood volume. In this study we used this technique to determine the effect
of hypoxia and hyperoxia on whole body autoregulation. Rats with an
arterial catheter for blood pressure measurement and an electromagnetic
flow probe for cardiac output measurement were placed in a chamber with a
controlled oxygen environment. Neurohumoral blockade was achieved with
chlorisondamine (10 mg/kg), methscopolamine (0.5 mg/kg), captopril (1
mg/kg), and [d(CH2)5Tyr(Me)]arginine vasopressin (10 micrograms/kg).
Hemodynamic variables were restored to normal with a constant
norepinephrine infusion. Group 1 (n = 7) underwent a 6-min infusion of
donor blood (0.9 ml) during hypoxia (Po2 = 52 +/- 3 mmHg) and hyperoxia
(Po2 = 296 +/- 12 mmHg). Group 2 (n = 8) was subjected to a 6-min
withdrawal of blood (0.9 ml) during hypoxia (72 +/- 2 mmHg) and hyperoxia
Po2 = 258 +/- 8 mmHg). The slope of the pressure-flow relationship was used
as an index of autoregulation so that a slope of 0 indicated complete
autoregulation and a slope of 1 represented no autoregulation. The
pressure-flow slopes with volume expansion were 0.54 during hypoxia and
0.15 during hyperoxia, while the slopes with volume contraction were 0.29
during hypoxia and 0.54 during hyperoxia. Thus, when arterial pressure was
raised above normal, the autoregulatory capacity was greater during
hyperoxia than with hypoxia. Conversely, when arterial pressure was lowered
below normal, the autoregulatory capacity was greater during hypoxia than
with hyperoxia.(ABSTRACT TRUNCATED AT 250 WORDS)
