Time course of mitosis and collateral growth following coronary microembolization in the porcine heart.

In ischaemic porcine myocardium, the growth of collateral vessels by angiogenesis is observed in clusters in the vicinity of focal necroses. Because mitosis of endothelial cells is a prerequisite for angiogenesis, the purpose of this study has been to evaluate the time course of mitosis as an indicator of vascular growth in a porcine model of coronary microembolization. Ischaemia was induced by injection of 25-microm microspheres in the left circumflex artery, followed by tissue collection from non-ischaemic and ischaemic areas of the same heart after 24, 72 or 168 h microembolization. Tissue was studied by histone H3 in-situ hybridization, PCNA/cyclin immunohistochemistry and electron microscopy. The number of blood vessels in ischaemic myocardium was compared with that in normal control tissue. Capillary growth started as early as 24 h after microembolization, as indicated by increasing numbers of proliferating, histone H3- and PCNA/cyclin-positive cells in the necrotic inflammatory foci of the ischaemic area. At 72 h and 168 h, the number of blood vessels was significantly higher in ischaemic than in normal myocardium, whereas at 168 h, mitosis of cells was, as in normal myocardium, a rare event. Coronary microembolization of porcine myocardium thus leads to an increased cellular proliferation rate between 24 h and less than 7 days after the onset of microembolization, followed by enhanced capillary growth. In-situ hybridization with histone H3 and PCNA/cyclin immunohistochemistry seem to be reliable markers for proliferation and vascular growth in non-cancerogenic tissue.