Oxygen consumption of nonfiltering dog kidneys

Basal renal O2 consumption and the efficiency of O2 utilization for Na+ reabsorption

We examined how the presence of a fixed level of basal renal O2 consumption (Vo2(basal); O2 used for processes independent of Na(+) transport) confounds the utility of the ratio of Na(+) reabsorption (TNa(+)) to total renal Vo2 (Vo2(total)) as an index of the efficiency of O2 utilization for TNa(+). We performed a systematic review and additional experiments in anesthetized rabbits to obtain the best possible estimate of the fractional contribution of Vo2(basal) to Vo2(total) under physiological conditions (basal percent renal Vo2). Estimates of basal percent renal Vo2 from 24 studies varied from 0% to 81.5%. Basal percent renal Vo2 varied with the fractional excretion of Na(+) (FENa(+)) in the 14 studies in which FENa(+) was measured under control conditions. Linear regression analysis predicted a basal percent renal Vo2 of 12.7-16.5% when FENa(+) = 1% (r(2) = 0.48, P = 0.001). Experimentally induced changes in TNa(+) altered TNa(+)/Vo2(total) in a manner consistent with theoretical predictions. We conclude that, because Vo2(basal) represents a significant proportion of Vo2(total), TNa(+)/Vo2(total) can change markedly when TNa(+) itself changes. Therefore, caution should be taken when TNa(+)/Vo2(total) is interpreted as a measure of the efficiency of O2 utilization for TNa(+), particularly under experimental conditions where TNa(+) or Vo2(total) changes.

Changes in arterial and cerebral venous blood gases, cerebral blood flow and cerebral oxygen consumption at different stages of thioacetamide-induced hepatogenic encephalopathy in rat

Rats were subjected to repeated intraperitoneal administrations of thioacetamide (TAA) in order to produce the following stages of hepatogenic encephalopathy (HE): the early stage, characterized by activation of brain metabolism (Group 1), the precomatose stage with impairment of brain metabolism (Group 2) and the stage of recovery (Group 3). A decrease of cerebral blood flow (CBF) of 50%, related to a drop of systemic arterial pressure and to increased hematocrit, were observed in groups 1 and 2 but not in group 3. However, the cerebral oxygen consumption (CMRO2), calculated from arterial venous difference in oxygen content and taking into account CBF, was markedly decreased in group 2, but remained unchanged in group 1. This reflects the state of cerebral metabolism at these stages. The results underscore the necessity of simultaneous monitoring of CBF and blood gases for distinguishing between the particular stages of HE revealed by biochemical tests.