The Vascular Myogenic Effect Of Ethanol And The Mechanism In Rat Isolated Middle Cerebral Artery

Objectives:To investigate the effects of different concentration of ethanol on the resting tone of rat isolated middle cerebral arteriole(MCA) rings; To explore the effects of ethanol on the MCA rings precontracted with U46619, KCl or ET; To explore the relationship between effects of ethanol on the MCA rings precontracted by U46619 and mitogen-activated protein kinase(MAPK), calcium channels.Methods:1. Procedures of rat isolated MCA rings. Male rats were killed by decapitation to take out the brain tissue and placed into 4℃ physiological salt solution(PSS) immediately.Middle cerebral arteries were separated under integrated microscope, cut into 2mm-long rings and mounted on a wire myograph. The tension changes of ethanol-induced contractions in MCA rings which was precontracted by U46619, KCl, ET were recorded by Power Lab and DMT systems. The maximal contraction induced by 60mmol/L KCl was taken as 100% and the percentage of contraction by each concentration of stimulator was calculated.2. L-type voltage gated Ca2+channels(LVGC) inhibitor Nifedipine(1.0× 10-7 mol/L),the extracellular Ca Cl2(2.5mmol/L), p38 MAPK inhibitor SB239063(3.0×10-6mol/L) and Extracellular signal-regulated kinase(ERK) inhibitor PD98059(3.0×10-6mol/L) were observed in ethanol-induced myogenic responses of isolated MCA rings which precontracted by U46619.Results:1. The effects of ethanol on the resting tone of isolated MCA ringsThe contractions of ethanol(0.1%, 0.3%, 1.0%) on the resting tone of MCA rings were:(0.04±0.06)m N,(0.08±0.08)m N,(0.10±0.08)m N, and the percentages of contraction were:(0.93±1.40)%,(1.84±1.66)%,(2.23±1.80)%. Compared with the control, there was no significant difference(P>0.05).2. The effects of ethanol on the isolated MCA rings which was precontracted by U46619, KCl, ETU46619(3.0×10-7mol/L), KCl(39mmol/L) and ET(3.0×10-9mol/L) induced contraction in the MCA rings. The tension of contractions were:(1.47±0.42)m N,(1.83±0.80)m N,(0.69±0.50)m N, and the percentages of contraction were(26.12±6.95)%,(24.66±8.94)%,(13.29±4.86)%. Ethanol contracted isolated MCA rings in a concentration-dependent manner on the basis of contraction induced by U46619, KCl and ET. The Emax values were:(5.2±2.06)m N,(3.83±2.30) m N,(2.91±1.28)m N, and the percentages of contraction were:(87.33±3.0)%,(47.33±10.24)%,(60.91±6.13)%. Compared with the effects of ethanol on the resting tension of isolated rat MCA rings, the effects of ethanol on the precontracted by U46619, KCl and ET has statistically significant difference(P<0.05).3. Effects of Nifedipine and Ca Cl2 on the ethanol-induced contraction in isolated MCA rings which precontracted by U46619(1)U46619(3.0×10-7mol/L) induced contraction in the MCA rings. The tension of contraction was(1.53±0.35)m N, and the percentage of contraction was(30.08± 5.60)%.Ethanol(0.1%~1.0%) obviously enhanced the contraction of isolated MCA rings induced by U46619 in a concentration-dependent manner, and the contraction percentages were:(17.96±4.03)%,(37.57±4.05)%,(85.16±5.67)%. Nifedipine(1.0×10-7mol/L) significantly inhibited the contraction of isolated MCA rings induced by ethanol(0.1%, 0.3%,1.0%)(P<0.05), and the percentages of contraction were:(2.25±2.79)%,(16.78±2.59)%,(65.13±7.98)%.(2)In Ca2+-free HEPES solution, U46619(3.0×10-7mol/L) induced contraction in the MCA rings, and the contraction was(0.19±0.10)m N, then 2.5mmol/L Ca Cl2 was added to the chamber, the contraction of rings attenuated to(1.31±0.44)m N. Ethanol(1.0%)significantly enhanced the contraction of rings induced by Ca Cl2(P<0.05), and the contraction was(3.21±1.43)m N. While U46619-induced contraction was not affected by ethanol(P>0.05).4. Effects of SB239063 and PD98059 on the ethanol-induced contraction in isolated MCA rings which precontracted by U46619(1)U46619(3.0×10-7mol/L) induced contraction in the MCA rings. The tension of contraction was(1.49±0.37)m N, and the percentage of contraction was(27.44± 2.78)%.Ethanol(0.1%~1.0%) obviously enhanced the contraction of isolated MCA rings induced by U46619 in a concentration-dependent manner, the contraction percentages were:(17.53±1.28)%,(36.18±2.98)%,(85.60±3.41)%. SB239063(3.0×10-6mol/L) obviously inhibited the contraction of isolated MCA rings induced by ethanol(0.1%, 0.3%,1.0%)(P<0.05), the contraction percentages were:(3.98±1.02)%,(17.85±2.96)%,(70.03±5.43)%.(2)U46619(3.0×10-7mol/L) induced contraction in the MCA rings, The tension of contraction was(1.44±0.66)m N, and the percentage of contraction was(28.25±1.74)%.Ethanol(0.1%~1.0%) obviously enhanced the contraction of isolated MCA rings induced by U46619 in a concentration-dependent manner, the percentages of contraction were:(20.18±2.67)%,(40.38±4.23)%,(86.58±4.95)%. PD98059(3.0×10-6 mol/L) significantly inhibited the contraction of isolated MCA rings induced by ethanol(0.1%, 0.3%,1.0%)(P<0.05), the contraction percentages were:(6.36±1.62)%,(22.00±4.45)%,(49.65±5.68)%.Conclusion:Ethanol obviously enhanced the contraction of isolated MCA rings induced by U46619, KCl and ET in a concentration-dependent manner, while it does not affect the resting tone; Activation of MAPK and extracellular Ca2+may be play important roles in the ethanol- induced contractions in rat isolated MCA rings.