| Object In the previous studies, we have found that phenytoin can accelerate the healing process after myocardial infarction in rat. The purpose of this work is to investigate the possible mechanisms underling this phenomenon by dynamic measurement of matrix metalloproteinase-2 and -9 activity and collagen changes in heart tissue in the early period after myocardial infarction in rat.Methods 175 adult male Wistar rats that survived ligatation of the left coronary artery were randomized to phenytoin group (100mg·kg-1·day-1 ip) or operation control and compared to sham-operated rats. The time-dependent proteolytic activity of MMP-2 and MMP-9 were detected by gelatin zymography serially. Clear bands on gelatin-mixed gel which were due to the existence and activity of MMP-2 and MMP-9 were quantified by Integrated optical density (IOD). Picrosirius red staining plus polarized light micrscopy was used for qualitative and quantitative analysis of collagen include collagen volume fraction (CVF) and ratio of type I /III collagen. In addition, Infarct thickness and myocyte cross sectional area were also evaluated by image analysis.Results 14 days after myocardial infartion (MI), phenytoin could reduceinfarct wall thinning. Mean thickness of infracted ventricular free wall was 3.16±0.55mm for control group and 4.00±0.84mm for phenytoin group (P < 0.01). Compared with control group, the rats received phenytoin had less myocyte cross-sectional area (372.12±70.55 versus 416.95±61.54 jj.m2, P < 0.01). 2 weeks after MI, CVF in two groups both had significantly dynamic increase and phenytoin could accelerate the beneficial change (76.81±8.32% versus 84.46±4.26%, P < 0.01). In contrast to control group, ratio of type I to type III collagen in phenytoin increased more quickly. 14 days after MI, phenytoin group achieved 36.88± 18.60, whereas operation control group is only 22.05±7.43(/><0.05). Apart from these results, phenytoin did little to CVF in non-infarcted region. Analysis of MMPs activity in myocardial extracts by zymography demonstrated that infarction-induced expression of proMMPs and active MMPs was both upregulated in phenytoin group and operation control. We found that after MI, MMP-9 activity increased as early as 1 day and reached a maximum then gradually descended, whereas MMP-2 started to increase rapidly and remain elevated for up to 14 days thereafter. Phenytoin seemed to enhance expression of MMP-2 and MMP-9. 1 day after MI, active MMP-9 in phenytoin group expressed an increasing trendency compared to MI control (3.50±1.25 versus 2.43±0.60).Conclusion The increase in collagen accumulation and the enhanced expression of MMPs compared with those of control group suggests that phenytoin can attenuate the degree of post-infarction left ventricular dilation and expansion of the infarct during the early phase of MI healing. MMP-2 and MMP-9 enhanced by phenytoin probably played a prominent role in the promoted inflammatory response, which may facilitate the wound healing... |
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