MECHANISMS OF THE FIRST AND SECOND WINDOW OF PROTECTION OF PREISCHAEMIC VAGAL STIMULATION ON MYOCARDIAL INFARCTION IN MICE

KELLY J; MÉNDEZ DIODATI N; MARCHINI T; FRANCO RIVEROS V; BERNATENÉ E; CASANOVA V; EVELSON P; BUCHHOLZ B; GELPI RJ

Mar del Plata

Congreso; LXIV reunión anual de la Sociedad Argentina de Investigación Clínica (SAIC); 2019

We recently proved that pVS mimics classic ischaemic preconditioning. Our objective was to study the chronology and mechanisms of the protective effect of VS, and to assess whether the protection is comprised of a first and second window. Mice were randomly assigned to different protocols (n=5-7 per group). The control group had 30 min of regional myocardial ischaemia and 2 h of reperfusion (I/R). The other groups underwent 10 min of pVS and either 5 min, 3-6-12-24-48-72 or 96 h of recovery between VS and I/R. The 5 min, 3 and 72 h groups were redone to receive a muscarinic receptor inhibitor (atropine). The 5 min and 72 h groups were performed yet again to administer a mitochondrial K+ ATP channel blocker (5-HD) and a nitric oxide synthase inhibitor (L-NAME). All groups were catheterised to assess ventricular function. Septum (S) and area at risk (AR) samples from the I/R, 5 min and 72 h groups were taken to assess mitochondrial active respiration (MAR), passive respiration (MPR), and the respiratory control ratio (RCR). Hearts were dyed with Evans Blue and incubated in TTC to measure IS. pVS-5min had smaller IS when compared to I/R (44±3% and 57±2%, respectively; p<0.05). The 3h and 6h groups showed further IS reduction (34±3% and 34±3%, respectively; p<0.05 vs 5min). Cardioprotection was lost at 12, 24 and 48 h post-VS (56±4%, 53±2%, 56±2%, respectively; p=NS vs I/R), but reappeared at 72 h post-VS (42±4%; p<0.05 vs pVS-48h) and was lost again at 96 h post-VS (56±3%; p=NS vs I/R). The IS-reducing effect of pVS-5min, 3 and 72 h was abolished by atropine (56±2%, 56±3% and 56±3%; p=NS vs I/R), 5-HD in pVS-5min and 72 h (55±2% and 62±5%, p=NS vs I/R) and L-NAME in pVS-5min and pVS-72h (56±3% and 57±2%, p=NS vs I/R). There were no significant differences between S and AR in any of the groups in MPR. MAR, however, was decreased in the AR of the I/R group when compared to the S (131±13 vs 83±8 p<0.05) and so was the RCR (5±0,2 vs 3±0,2 p<0.01). This difference was reversed in the 5 min group both in the MAR (128±12 vs 126±11 p=ns) and in the RCR (4±0,3 vs 4±0,2 p=ns). However, in the 72h group, the difference persisted both in MAR (150±5 vs 109±5,7 p<0.01) and in RCR (4±0,1 vs 3±0,1 p<0.01). In conclusion, VS has two protection windows as does classic preconditioning. The first window lasts 6 h and the second window appears at 72 h and disappears at 96 h. The mechanisms underlying the cardioprotective effect include muscarinic receptors, nitric oxide synthase and mitochondrial K+ ATP channels and functional changes in mitochondrial oxygen consumption.