Estimation of an area between the baseline and the effect curve parameter for lactate levels in the hippocampi of neonatal rats during anesthesia

Naturally occurring caspase-3-dependent cell death is a widespread event in the immature nervous system. Prolonged exposure to anesthetics promotes activation of caspase-3 in the developing hippocampus. In addition, anesthetics can upregulate the levels of metabolite lactate in the adult brain. The long-lasting increase in lactate levels may affect viability of brain cells. However, it remains unknown if anesthetic-induced activation of caspase-3 is accompanied by an increase in lactate levels in the immature brain. We investigated expression of apoptotic proteins by immunoblot and estimated an area between the baseline and the effect curve (ABEC) parameter for lactate levels by high-resolution magnetic resonance spectroscopy in the hippocampi of 2-day-old Wistar rats after treatment with anesthetic urethane. Both 1.5 and 2.5 g/kg of urethane resulted in a dose-dependent increase in the levels of active caspase-3 in the hippocampi in 4 h after injection. This anesthetic-induced increase in the levels of active caspase-3 was preceded by a prolonged dose-dependent rise in lactate levels. The dose-dependent increase in lactate levels was not associated with the urethane-induced changes in respiratory rate in the treated rat pups. Present results evidence that the prolonged dose-dependent elevation in lactate levels in the developing brain can be induced even by urethane, which was suggested to be suitable for various physiopharmacological studies previously. The observed sequence of events after treatment with urethane suggests the possible role of lactate as a neurodamaging agent in the immature brain in case of the sustaining rise in the levels of this metabolite during prolonged anesthesia.