DEVELOPMENTAL-CHANGES IN NEWBORN LAMB BRAIN MITOCHONDRIAL ACTIVITY AND POSTASPHYXIAL LIPID-PEROXIDATION

Previously, our laboratory has demonstrated inhibition of mitochondria l state 3 (ADP-dependent) respiration 5 min after resuscitation from a n asphyxial insult in lambs less than 3 days of age. Older lambs were resistant to this transient mitochondrial dysfunction. This study was designed to examine if age-related differences in baseline state 3 mit ochondrial respiration, electron transport chain activity, or suscepti bility to oxygen free radical-mediated lipid peroxidation were related to the previously observed differences in postasphyxial mitochondrial respiration. Mitochondrial respiration was measured in 24 nonasphyxia ted control lambs aged 1-10 days using four different substrates. Elec tron transport chain activity was assessed in 15 of these lambs, and l ipid peroxidation measured as conjugated diene production was measured in 11 of these lambs. These lambs were all ventilated to maintain nor mal blood gases for a time period equal to the length of the hypoxic i nsult in asphyxiated lambs (see below), after which samples of brain w ere removed for isolation of mitochondria. A second group of 11 lambs( seven less than or equal to 3 days of age and four >3 days of age) wer e asphyxiated. The insult was a 75-to-90-min episode of hypoxia and hy percarbla that resulted in bradycardia and systemic hypotension over t he final 15 min of the insult. At the end of asphyxia, the lambs were resuscitated and returned to control ventilator settings. Samples of b rain were removed 5 min after resuscitation. Postasphyxia electron tra nsport chain activity end lipid peroxidation were measured, All measur ements described above were done in both nonsynaptic (primarily glial in origin) and synaptic mitochondria. State 3 mitochondrial respiratio n varied significantly with age, decreasing by an average of 41.2% +/- 11.1%(mean +/- SEM) from Day 2 to Day 5-6 and then increasing back to levels similar to Day 2 by Day 8-10 in nonsynaptic mitochondria. Stat e 3 respiration in synaptic mitochondria decreased 60.6% +/- 5.2% from Day 2 to Day 5-6 before returning to levels similar to Day 2 by Day 8 -10. Resting (nonADP-dependent) state 4 respiration demonstrated simil ar developmental patterns. Electron transport chain activities did not vary with age in the nonasphyxiated control animals. In addition, an asphyxial insult did not diminish electron transport chain activities in either lambs less than or equal to 3 days old or those >3 days of a ge. In the less than or equal to 3-day-old animals, lipid peroxidation (measured as conjugated diene production) was 0.755 +/- 0.19 (Abs 233 /mg lipid; mean +/- SEM) in controls and 1.31 +/- 0.28 post-asphyxia ( P < 0.03) in nonsynaptic mitochondria, Synaptic mitochondria conjugate d diene productions were 0.561 +/- 0.05 and 1.369 +/- 0.27 (P < 0.004) , respectively. No differences in conjugated diene production between control end postasphyxia lambs were present in animals >3 days old. Th ese date are consistent with the conclusion that lambs less than or eq ual to 3 days old were more susceptible to oxygen free radical-mediate d lipid peroxidation than those >3 days of age.