BACKGROUND: A brief episode of cerebral ischemia confers transient ischemic tolerance to a subsequent ischemic challenge. We examined the effect of ischemic and hypoxic preconditioning in the neonatal rat.

METHODS: Seven-day old Sprague-Dawley rat pups were divided into three groups:control (n = 53), ischemic preconditioning (n = 51), and hypoxic preconditioning (n = 48). For ischemic preconditioning, the right common carotid artery was occluded for 10 min. Rats in the hypoxic preconditioning group were kept under hypoxic (8% oxygen/92% nitrogen) conditions for 4h. Twenty-four hours after the preconditioning, rats from all groups were exposed to the right common carotid artery ligature, followed by 2.5 h of hypoxia. Lipid/N-acetyl aspartate (Lip/NAA) and lipid/creatine (Lip/Cr) ratios from ¹H MR spectroscopy and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) were evaluated as measures of apoptosis 1 and 7 days after hypoxic-ischemic injury.

RESULTS: In the ischemic and hypoxic preconditioning groups, the Lip/NAA and Lip/Cr ratios and the numbers of TUNEL-positive cells were significantly lower than those in the control group (P < 0.05), but there were no significant differences between the two preconditioning groups.

CONCLUSIONS: These results suggest that ischemic and hypoxic preconditioning in the neonatal rat attenuate the apoptosis that is caused by hypoxic-ischemic brain injury.