Effects of mild hypothermia on β-adrenergic signaling pathway in a cardiac arrest swine model / 中华危重病急救医学

ABSTRACT

Objective To observe the effect of mild hypothermia on myocardial β-adrenergic receptor (β-AR) signal pathway after cardiopulmonary resuscitation (CPR) in pigs with cardiac arrest (CA) and explore the mechanism of myocardial protection. Methods Healthy male Landraces were collected for reproducing the CA-CPR model (after 8-minute untreated ventricular fibrillation, CPR was implemented). The animals were divided into two groups according to random number table (n = 8). In the mild hypothermia group, the blood temperature of the animals was induced to 33 ℃ and maintained for 6 hours within 20 minutes after return of spontaneous circulation (ROSC) by using a hypothermia therapeutic apparatus. In the control group, the body temperature of the animals was maintained at (38.0±0.5)℃ with cold and warm blankets. The heart rate (HR), mean arterial pressure (MAP), the maximum rate of increase or decrease in left rentricular pressure (+dp/dt max)were measured during the course of the experiment. The cardiac output (CO) was measured by heat dilution methods before CA (baseline), and 0.5, 1, 3, 6 hours after ROSC respectively, the venous blood was collected to detect the concentration of cTnI. Left ventricular ejection fraction (LVEF) was measured with cardiac ultrasound before CA and 6 hours after ROSC. Animals were sacrificed at 6 hours after ROSC and the myocardial tissue was harvested quickly, the mRNA expression of β1-AR in myocardium was detected by reverse transcription-polymerase chain reaction (RT-PCR), the contents of adenylate cyclase (AC) and cyclic adenosine monophosphate (cAMP) were detected by enzyme linked immunosorbent assay (ELISA), the protein content of G protein-coupled receptor kinase 2 (GRK2) was detected by Western Blot. Results After successful resuscitation, the HR of both groups were significantly higher than the baseline values, CO, ±dp/dt max were significantly decreased, MAP were not significantly changed, serum cTnI levels were significantly increased. Compared with the control group, HR at 0.5, 1, 3 hours after ROSC were significantly decreased in mild hypothermia group (bpm 142.80±12.83 vs. 176.88±15.14, 115.80±11.48 vs. 147.88±18.53, 112.60±7.40 vs. 138.50±12.02, all 1 < 0.01), CO was significantly increased at 1 hours and 3 hours after ROSC (L/min 3.97±0.40 vs. 3.02±0.32, 4.00±0.11 vs. 3.11±0.59, both 1 < 0.01), +dp/dt max at 3 hours and 6 hours was also significantly increased after ROSC [+dp/dt max (mmHg/s) 3 402.5±612.7 vs. 2 130.0±450.6, 3 857.5±510.4 vs. 2 562.5±633.9; -dp/dt max (mmHg/s) 2 935.0±753.2 vs. 1 732.5±513.6, 3 520.0±563.6 vs. 2 510.0±554.3, all 1 < 0.05], the cTnI was significantly decreased at 3 hours and 6 hours afher ROSC (μg/L 1.39±0.40 vs. 3.24±0.78, 1.46±0.35 vs. 3.78±0.93, both 1 < 0.01). The left at 6 hours after ROSC in both groups was decreased as compared with that before CA. The LVEF in the mild hypothermia group was higher than that in the control group (0.52±0.04 vs. 0.40±0.05, 1 < 0.05). The mRNA expression of β1-AR, and concentrations of AC and cAMP in hypothermia group were significantly higher than those in control group [β1-AR mRNA (2-&Delta;&Delta;CT) 1.18±0.39 vs. 0.55±0.17, AC (ng/L)197.0±10.5 vs. 162.0±6.3, cAMP (nmol/L) 1 310.58±48.82 vs. 891.25±64.95, all 1 < 0.05], GRK2 was lower than that in the control group (GRK2/GAPDH 0.45±0.05 vs. 0.80±0.08, 1 < 0.05). Conclusion Mild hypothermia can reduce the degree of cardiac function injury after CPR, and its mechanism may be related to the reduction of impaired myocardial β-AR signaling after CPR.