DELAYED TREATMENT WITH ALPHA-PHENYL-N-TERT-BUTYL NITRONE (PBN) ATTENUATES SECONDARY MITOCHONDRIAL DYSFUNCTION AFTER TRANSIENT FOCAL CEREBRAL-ISCHEMIA IN THE RAT

The present experiments were undertaken to explore the mechanisms of s econdary brain damage in focal ischemia of long duration (2 h), follow ed by recirculation, Recirculation has previously been found to cause partial recovery and secondary deterioration of cellular bioenergetic state, the subsequent damage being ameliorated by a free radical spin trap, alpha-phenyl-N-tert-butyl nitrone (PEN), even when the drug was given 1 (or 3) h after the start of recirculation. Our objective was t o assess whether the secondary deterioration of the cellular bioenerge tic state is due to mitochondrial dysfunction and to study whether PEN acts by preventing secondary damage to mitochondria. Focal and perifo cal (''penumbral'') tissues were sampled after 2 h of ischemia and aft er 1, 2, and 4 h of recirculation; at the latter two times, vehicle- a nd PEN-injected animals were studied, PEN being given after 1 h of rec irculation. Homogenates were prepared, and stimulated (+ADP), nonstimu lated (-ADP), and uncoupled respiratory rates were measured polarograp hically. The results were similar in focus and penumbra, albeit more p ronounced in the focus. Ischemia was associated with a decrease in ADP -stimulated and uncoupled respiration rates, with a marked fall in the respiratory control ratio, defined as ADP-stimulated divided by nonst imulated respiration. Recirculation (1 h) brought about partial recove ry, but continued reflow (2 and 4 h) was associated with a secondary d eterioration of respiratory functions. This deterioration was prevente d by PEN, given 1 h after the start of recirculation, The results rais e the question whether the secondary deterioration of the cellular bio energetic state in focal ischemia-reperfusion is due to secondary mito chondrial dysfunction and whether the amelioration of the subsequent d amage by PEN is partly or wholly due to the effect of the spin trap on the mitochondria. (C) 1996 Academic Press, Inc.