Effect of Ringer infusion on ischemic acute renal failure: caution on interpreting the results of short-term studies.

The effect of a 4.5 mL/h Ringer infusion on the recovery from a unilateral 40-min renal artery occlusion was investigated in Sprague-Dawley rats. The inulin clearance measured in the experimental kidney 24 and 48 h after the insult in control animals that did not receive the Ringer infusion was 0.14 +/- 0.10 (mean +/- SE) and 0.11 +/- 0.05 mL/min, respectively. In animals that received 24 h of Ringer infusion begun at the time of the renal artery occlusion the inulin clearance was 0.81 +/- 0.07 mL/min, a value significantly higher than either of the control groups (p less than .05). If, however, the Ringer infusion was stopped at 24 h and the inulin clearance measured at 48 h, it had decreased significantly (0.27 +/- 0.09 mL/min) and was no longer greater than the control groups. Similarly, if the infusion was continued for 48 h there was no longer a significant difference between the inulin clearance (0.37 +/- 0.11), when compared with 48 h of no infusion (0.11 +/- 0.05). The histology of the different groups corresponded with the functional data. We conclude that 24 h of Ringer infusion leads to functional and histological protection when measured at 24 h; however, if measured at 48 h, protection is no longer evident. These studies suggest that caution should be exercised in extrapolating from the results of protective maneuvers in ischemic acute renal failure investigated by short-term studies.

Oxidant stress following renal ischemia: changes in the glutathione redox ratio.

Pretreatment of animals with certain antioxidant enzymes and substances decreases renal damage following ischemia and reperfusion. The hypothesis that reoxygenation imposes an oxidant stress has been used to explain this. The present study has directly assessed oxidant stress under these conditions by measuring the glutathione redox ratio ([GSSG/(GSH + GSSG)] x 100) in freeze-clamped kidney. The glutathione peroxidase system plays a role in removing peroxides which result from oxidant stress, generating GSSG from GSH in the process. The selenium-dependent glutathione peroxidase can metabolize H2O2 and other hydroperoxides. A non-selenium-dependent glutathione peroxidase activity is present and can metabolize organic hydroperoxides, but it cannot metabolize H2O2. Under anesthesia, the left renal artery was occluded for 40 minutes and then reflow was allowed. Kidneys were freeze clamped before reflow and after 5, 10, and 15 minutes of reflow. The contralateral kidney was freeze clamped and used as a control. The control value for the glutathione redox ratio was 1.09 +/- 0.05. This fell during ischemia to 0.67 +/- 0.22 and increased significantly to 1.66 +/- 0.29 after five minutes of reperfusion. By 15 minutes it had returned to 1.09 +/- 0.22. Treatment of rats with diquat, which causes a severe oxidant stress, raised the glutathione redox ratio from 0.88 +/- 0.12 to 1.89 +/- 0.15. Thus, reperfusion was concluded to cause a large but transient oxidant stress. Selenium-deficient rats were used to examine the nature of the oxidant stress. Activity of the selenoenzyme glutathione peroxidase was depressed to 2% of control in the kidneys of these rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide, right atrial pressure, and sodium excretion rate in the rat.

This study examined the relationship between right atrial pressure (RAP), urine flow rate, sodium excretion rate, and plasma atrial natriuretic peptide (ANP) levels after an acute Ringer expansion. Two groups of rats had their RAP monitored and balloon catheters placed in their thoracic inferior venae cavae. In one group the balloon remained deflated, and in the second group the balloon was inflated during the volume expansion in an attempt to prevent the rise in RAP. The peak RAP was 7.3 +/- 0.8 mmHg when the balloon remained deflated and 3.5 +/- 0.6 mmHg in the group with the balloon catheter inflated (P less than 0.005). The corresponding peak ANP levels were 682 +/- 140 and 223 +/- 40 pg/ml. There was a significant correlation between the peak RAP and ANP levels (r = 0.754; P less than 0.05). The inflation of the balloon catheter significantly decreased the urine flow rate and the urine sodium excretion rate. A final group of animals had 200 microliters of rabbit serum containing antibody to ANP infused before the volume expansion. The antibody-treated animals had significantly lower urine flow and sodium excretion rates than nonantibody-treated control rats. We conclude that ANP is one of the factors which allows the rat to excrete an acute Ringer expansion.