Nucleotide Resynthesis Research Articles

Postischemic hemodynamics and recovery of renal adenosine triphosphate.

Renal vasoconstriction is an important pathophysiological component of an ischemic acute renal injury. The postischemic infusion of ATP-MgCl2 enhances recovery of glomerular and tubular function, accelerates regeneration of sublethally injured tubular cells, and augments resynthesis of cellular nucleotides. Since both ATP and MgCl2 are vasoactive compounds, postischemic enhancement of renal blood flow (RBF) by a pharmacological agent, dopamine, was examined to study the possible contribution of vasodilation. At 2 h, the infusion of dopamine resulted in RBF (1.70 +/- 0.09 ml X min-1 X 100 g body wt-1 X kidney-1) and inulin clearance (CIn, 400 +/- 44 microliter X min-1 X 100 g body wt-1) similar to rats treated with ATP-MgCl2 (1.73 +/- 0.27 RBF, 404 +/- 38 CIn) and significantly (P less than 0.01) greater than saline-treated rats (0.80 +/- 0.04 RBF, 78 +/- 19 CIn; P less than 0.01). However, by 24 h CIn in dopamine animals had not continued to improve (460 +/- 25 microliter X min-1 X 100 g body wt-1) and was similar to normal saline rats (388 +/- 40). In contrast, CIn in ATP-MgCl2 animals showed sustained recovery (676 +/- 28 microliter X min-1 X 100 g body wt-1, P less than 0.01). These differences resulted from improved integrity of tubular epithelium as reflected by decreased cell swelling and necrosis. Moreover, the recovery of renal ATP levels, as assessed by 31P nuclear magnetic resonance, in animals given saline (63 +/- 3%) or dopamine (66 +/- 5%) was slow and incomplete by 120 min after ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection of kidneys after prolonged ischemia against reoxygenation injury by temporary inhalation of a hypoxic gas mixture

Temporary hypoxemia as a method of protecting an organ against reoxygenation injuries could be used in cases when prophylactic antioxidant therapy has been overlooked or is impossible, but the protective effect of inhalation of HGM has been demonstrated previously in acute experiments only, and the animals were not subsequently transfer'red to breathing ordinary air. In the present investigation the protective action of temporary inhalation of HGM on function of the kidneys rendered ischemic for 2 h was studied in chronic experiments, the required duration of such inhalation was determined, and correlation was established between the protective effect of HGM and the rate of resynthesis of adenine nucleotides (ADN) in the organ. EXPERIMENTAL METHOD Experiments were carried out on 250 August and Wister rats weighing 120-200 g. Renal ischemia was produced under hexobarbital anesthesia {70 mg/kg) by applying microclips to the vascular pedicle of both kidneys, isolated from the perinephric cellular tissue. The clips were removed after 2 h, during which time the rats breathed ordinary air or inhaled an HGM containing 10-12% oxygen or pure oxygen through a mask. Inhalation of the gas mixtures began 5 rain before the beginning of reperfusion of the kidneys. After suture of the wound in the abdominal wall the rats were kept for 4 or 24 h in a chamber ventilated with the same gas at the rate of 2 liters/min, after which they were transferred to breathing air. Stable humidity (85-90%) and temperature (23-25~ were maintained in the chamber. The oxygen concentration in the gas mixture and chamber was recorded by an oximeter (Beckman, USA) and pO 2 and HbO 2 in the rats' blood were determined on a micro-Astrup apparatus. To compare the protective effect of HGM with the effect of antioxidants, 29 rats were given an intraperitone~/1 injection of 240 mg/kg of ionol (2,6-di-tertbuty l-4-methylphenol ) 24 h before

Incorporation of 15N-leucine amine into ATP of fast-twitch muscle following stimulation

During intense contraction conditions, ATP content in fast-twitch muscle rapidly decreases (approx. 50%) by the deamination of AMP to IMP and NH 3. During recovery, the ATP content returns to normal by the reamination of IMP from aspartate. We evaluated whether the donor amine may be obtained from branched chain amino acid uptake by perfusing muscle in situ with 1.0 mM [ 15N]-leucine during a 1 hr recovery. [ 15N]-enriched adenine nucleotide accounted for 14% to 24% of the IMP reaminated, depending on whether [ 15N]-leucine was provided only during the recovery period or, in addition, 30 min prior to stimulation. Thus, the uptake of leucine by fast-twitch muscle may provide an important source of amine for adenine nucleotide resynthesis following contractions.

Nucleotide degradation and functional impairment during cardioplegia: amelioration by inosine.

The degradation of adenine nucleotide levels and impairment of functional recovery associated with exposure to hypothermic (20 degrees C) cardioplegia was studied in 84 isolated working rat hearts. After a 1-hour control period, hearts were exposed to 1 hour of cardioplegia that consisted of increasingly longer periods of cardioplegic solution (CPS) infusion (30 seconds and 10, 30 and 60 minutes), followed by increasingly shorter periods of global ischemia (591/2 minutes and 50, 30 and 0 minutes). Hearts were then reperfused for 1 hour with control perfusate, during which recovery of cardiac output was monitored. Additional hearts were freeze-clamped at various points in the protocols to determine adenine nucleotide levels (ATP, ADP, AMP and their sum TAN). Exposure to increasingly longer periods of CPS perfusion resulted in proportionally greater degradation of nucleotides and poorer recovery of cardiac output. Addition of inosine to the recovery perfusate as well as the CPS further improved nucleotide levels and recovery of cardiac output. These results suggest that washout of nucleotide degradation products in the CPS or reperfusion prevents their salvage for nucleotide resynthesis and impairs functional recovery from cardioplegia.

Prolonged depletion of ATP and of the adenine nucleotide pool due to delayed resynthesis of adenine nucleotides following reversible myocardial ischemic injury in dogs

After 15 min of severe ischemia induced by circumflex artery occlusion in open-chest dogs, 65% of the ATP and 50% of the total adenine nucleotide (ΣAd) pool is lost from the subendocardial myocardium [ 12]. Nevertheless, this injury is reversible if the affected tissue is reperfused with coronary arterial blood. In the present experiment, we assessed the effects of various periods of arterial reflow following 15 min of ischemic injury, on resynthesis of ATP and ΣAd. The circumflex artery was occluded for 15 min and reperfused for 20 or 60 min, or 24 or 96 h. Ten seconds prior to excision of the heart, the circumflex artery was reoccluded and the fluorescent dye thioflavine S was injected intravenously in order to identify the ischemic or the reperfused tissue which had been ischemic. The mean ATP after 15 min of ischemia was reduced 62% from 5.42 ± 0.33 to 2.08 ± 0.21 μmol/g; and the total nucleotide content was reduced by 50%. ATP content recovered slightly during the first 20 min of reperfusion but remained markedly depressed for at least 24 h because of the initial depletion of adenine nucleotides and because minimal salvage or de novo synthesis occurred in the injured muscle during this time period. By 4 days, ATP and total adenine nucleotides were still slightly depressed but had recovered to 88% and 91% of control. Electrolyte changes and an increased inulin diffusible space, which are characteristic of irreversibly injured myocardium reperfused for 20 or 60 min, were not observed. Also tissue necrosis was absent in the hearts reperfused for 24 or 96 h. These observations indicate that the marked depression of ATP and adenine nucleotides and the slow recovery of these metabolites occurred in myocardium which nevertheless was reversibly injured in terms of cellular viability.