Cerebral metabolic response and mitochondrial activity following insulin-induced hypoglycemia in newborn lambs

We evaluated the newborn lamb's cerebral cellular activity and metabolism following acute insulin-induced hypoglycemia. Eleven animals received an insulin bolus followed by a continuous infusion to maintain a plasma glucose of 1 mM/l for 2 h, while 8 other animals received an equivalent dose of saline. Following the induction of hypoglycemia, the animals became quiet and transient seizures were observed in 3 animals. A significant increase in heart rate (p less than 0.01), and a decrease in arterial PaCO2 at 30 min (p less than 0.01), and pH at 2 h (p = 0.02), following hypoglycemia, were observed in the experimental group. Hypoglycemia did not significantly alter the cerebral blood flow, mitochondrial respiratory control ratio or the state-3 activity. The cerebral arteriovenous difference (CAVD) for oxygen did not change, while the glucose CAVD was significantly reduced from 0.47 +/- 0.21 to 0.24 +/- 0.16 mM/l (p less than 0.05) at the end of the hypoglycemia period, suggesting consumption of alternate substrates of energy by the brain. Insulin-induced hypoglycemia was associated with a significant increase in arterial lactate (p less than 0.01), and a significant correlation (p less than 0.01) between arterial and CAVD for lactate and beta-hydroxybutyrate (BOB) was observed. Cerebral consumption of alternate substrates of energy was inconsistent, and only observed for lactate in 5 and for BOB in 3 experimental animals following hypoglycemia. These data indicate that the newborn lamb's cerebral cellular activity is not affected by the degree of hypoglycemia achieved in these studies.(ABSTRACT TRUNCATED AT 250 WORDS)