Introduction
Cardiac arrest (CA) claims approximately 500,000 lives in the US alone. Despite recent advances in CPR, outcome remains poor. 17beta - estradiol, the principal mammalian estrogen, has been shown to reduce infarction size in experimental stroke 1 . Postischemic estrogen improves recovery of cerebral blood flow after stroke in rats 2 . The purpose of this study was to determine if chronic treatment with 17beta - estradiol (E2) after experimental cardiac arrest / cardio pulmonary resuscitation (CA/CPR) improves neuronal survival in male mice and if the E2 loading dose is important to alter outcome.
Methods
With institutional approval 60 male C57/Bl6 mice (22–26 g) were anesthetized with halothane, the jugular vein was catheterized, ECG was monitored, the trachea was intubated and controlled ventilation was performed throughout the experiment. CA was induced by i.v. injection of KCl. After 10 min, CPR was initated by chest compressions (∼300/min), administration of iv epinephrine (8 mg) and ventilation with 100% oxygen, as previously described 3 . 1.5 min after return of spontaneous circulation (ROSC) iv injection of either vehicle, 0.5 or 2.5 mg E2 (loading dose) was performed. Animals received additional s.c. silastic oil implants or hormone implants (12 mg E2) 30 min after ROSC, according to treatment group. Animals were re-anesthetized three days after ROSC, blood samples for E2 serum levels were taken followed by transcardial perfusion fixation (formalin 10%). Brains were removed for standard injury quantification in hippocampus (CA1) and caudoputamen (CP; hematoxylin-eosin staining, light-microscopy). Statistical analysis was performed using ANOVA.
Results
Physiologic variables, epinephrine dose and duration of CPR were not different between groups. 13 animals of the vehicle group, 16 of the 0.5+12 E2 and 17 of the 2.5+12 E2 group survived the three- day observation period. E2 serum levels were: vehicle=28±2, 0.5+12 E2=165±10 and 2.5+12 E2=153±11 pg/ml (p<0.001; mean±SE). Neuronal injury in rostral CP was less with 0.5+12 E2 (41±5% injured neurons) and 2.5+12 E2 (36±6%) administration, compared to vehicle (68±2%, p<0.001). Both E2 groups had improved neuronal survival in the caudal CP (0.5+12 E2: 46±5%, 2.5+12 E2: 35±5%), compared to vehicle (69±2%, p<0.05). CA1 injury was similar in all groups.
Conclusion
17b - estradiol application after CA/CPR improves neuronal survival in male mice. Protection is equally robust with both loading doses used. E2 treatment might play an important role in brain resusciation after cardiac arrest / CPR in humans.