Mitochondrial function after asphyxia in newborn lambs.

We examined mitochondrial oxidative function 5 minutes and 2 hours after a gradual asphyxial insult in newborn lambs. We subjected 16 ventilated newborn lambs to 75-90 minutes of hypoxia and hypercarbia that resulted in bradycardia and systemic hypotension over the final 15 minutes of the insult. At the end of asphyxia, the lambs were resuscitated and returned to control ventilator settings. Samples of brain were removed 5 minutes (n = 8) and 2 hours (n = 8) after asphyxia. Each group of eight lambs was subdivided into those less than 3 or greater than 3 days old to evaluate the effect of age on postasphyxia mitochondrial function. After classification into nonsynaptic and synaptic mitochondria, mitochondrial respiration (oxygen consumption) was measured using five different substrates. Data from asphyxiated lambs were compared with that from a control group of ventilated nonasphyxiated lambs (n = 8). In the lambs less than 3 days old, there was significant depression of mean +/- SEM nonsynaptic mitochondrial state 3 (adenosine diphosphate-dependent) respiration to 29.5 +/- 5.2% of control with four of the five substrates and of state 4 respiration to 33.7 +/- 0.9% of control with three of the five substrates 5 minutes after asphyxia. By 2 hours after asphyxia, mean +/- SEM nonsynaptic mitochondria state 3 respiration increased to 70.4 +/- 6.4% of control while state 4 respiration increased to 58.2 +/- 4.5% of control. In contrast, lambs greater than 3 days old exhibited no inhibition of nonsynaptic mitochondrial function after asphyxia.(ABSTRACT TRUNCATED AT 250 WORDS)