AJP - Heart and Circulatory Physiology, Vol 246, Issue 5 671-H674, Copyright © 1984 by American Physiological Society
Hypercapnia potentiates renal vasoconstriction during hemorrhagic hypotension in awake rabbits
D. W. Busija
Although both hemorrhagic hypotension and hypercapnia increase renal
vascular resistance (RVR) modestly, effects of interaction between these
stimuli on RVR have not been examined systematically in unanesthetized
animals. The purpose of this study was to test the hypothesis that renal
vasoconstriction during hemorrhagic hypotension is affected by arterial CO2
tension (PCO2). Unanesthetized rabbits were placed into an environmental
chamber, and six were exposed to normocapnia (PCO2 approximately 29 mmHg)
and six to hypercapnia (PCO2 approximately 62 mmHg). Renal blood flow (RBF)
was measured with 15-micrograms microspheres during 1) normotension [mean
arterial pressure (MAP) 84-88 mmHg]; 2) moderate hemorrhagic hypotension
(MAP 61-64 mmHg); and 3) severe hemorrhagic hypotension (MAP 44-50 mmHg).
When MAP was normal, RBF was 437 +/- 59 and 345 +/- 59 ml X min-1 X 100 g-1
in the normocapnic and hypercapnic groups, respectively (NS; P greater than
0.05). In addition, RVR (MAP/RBF) was 0.22 +/- 0.04 in the normocapnic
group and 0.32 +/- 0.08 mmHg X ml-1 X min X 100 g in the hypercapnic group
(NS; P greater than 0.05). During moderate hypotension, RVR was 0.48 +/-
0.18 in the normocapnic group and 1.74 +/- 0.36 mmHg X ml-1 X min X 100 g
in the hypercapnic group (P less than 0.05, comparison between groups).
During severe hypotension, RVR was 0.46 +/- 0.14 and 3.13 +/- 1.13 mmHg X
ml-1 X min X 100 g during normocapnia and hypercapnia, respectively (P less
than 0.05, comparison between groups). Thus, in unanesthetized rabbits,
although hypercapnia does not increase RVR compared with normocapnia when
arterial pressure is normal, hypercapnia greatly potentiates renal
vasoconstriction during hemorrhagic hypotension.
