Regional changes of polyamine profiles after reversible cerebral ischemia in mongolian gerbils: Effects of nimodipine and barbiturate

Abstract

The present experiments were undertaken to study whether the therapeutic inhibition of ischemic cell injury affects the postischemic disturbances in polyamine metabolism. Near complete forebrain ischemia was produced in Mongolian gerbils (Meriones unguiculatus) by occluding both common carotid arteries. Gerbils were subjected to 5 min cerebral ischemia and then immediately upon recirculation injected intraperitoneally with nimodipine (1.5 mg/kg;n=5) or pentobarbital (50 mg/kg;n=5). Untreated animals received the nimodipine vehicle whilst sham-operated animals served as controls. Following 96 h recirculation animals were reanesthetized and brains were frozen in liquid nitrogen. Polyamines (putrescine, spermidine, and spermine) were measured in samples (2–4 mg each) taken from the cerebral cortex and the CA1-subfield of the hippocampus. In addition, 10 μm thick coronal sections were prepared from the level of the dorsal hippocampus to determine histologically the extent of ischemic neuronal damage; this was quantified in the CA1-subfield of the hippocampus by counting the number of total and viable neurons/mm stratum pyramidale. In untreated animals reversible cerebral ischemia produced a significant increase in putrescine and a decrease in spermine in the CA1-subfield of the hippocampus (increase in putrescine from 11.3±0.6 to 41.8±3.6 nmol/g,p<0.01; and decrease in spermine from 351±26 to 161±16 nmol/g,p<0.05). Spermidine, in contrast, did not change during recirculation in the hippocampus. In the cerebral cortex postischemic polyamine levels were not significantly different from those found in control animals. In all untreated animals subjected to reversible cerebral ischemia severe cell necrosis could be observed in the CA1-subfield of the hippocampus. It proved possible to inhibit significantly both ischemia-induced disturbances of polyamine metabolism and ischemic cell injury in the CA1-subfield of the hippocampus by barbiturate treatment (p<0.05). The effect of nimodipine on ischemic cell injury and ischemia-induced changes of polyamine levels was not significant. In all experimental animals the putrescine levels in the CA1-sector of the hippocampus correlated with the extent of ischemic cell damage in a threshold relationship: in animals in which the putrescine levels lay below 15 nmol/g less than 5% of neurons were damaged, whereas in animals with putrescine levels above 25 nmol/g only about 5% of neurons in the stratum pyramidale survived the 5 min cerebral ischemic period. We conclude that putrescine may be viewed as an important biochemical correlate of ischemic cell injury.