Angiogenesis in rat aorta ring explant cultures.

This report describes the utilization of rat aorta "rings" as explants to study angiogenesis. Under short-term culture conditions, ring explants transferred at 3- to 4-day intervals showed growth (differential migration) of endothelial and/or smooth muscle cell populations. On the other hand, explants maintained for long-term (up to 3 weeks) without transfer, developed extensive out-growths of new vascular channels radiating on and through the established cell sheet. Examination of adventitia stripped ring segments, before culture revealed the presence of areas containing small vessel remnants embedded in the outer aorta wall. In addition, cultures of adventitial tissue alone yielded a variety of cell types including the occasional presence of vascular cells with developing channel formation. Immunofluorescent and ultrastructural examination of long-term aorta explant cultures revealed that these channels consisted of endothelial cells that exhibited positive reactivity for factor VIII antibody. In order to determine the influence of aorta-derived cells on vascular channel development, various vessel treatments and manipulations were performed before explant culture, to eliminate the influence of either the endothelium and/or adventitia-associated microvasculature remnants. Thus results clearly showed that the presence of both constituents is required to initiate the angiogenic response in this in vitro culture model. In addition, short-term aortic ring explant culture is an efficient and reliable technique for the isolation and culture of endothelium and smooth muscle cells from large vessels of the rat. More importantly, long-term maintenance of aorta explant cultures provides a novel self-contained system to study new vessel growth and development, and represents an attractive alternative model for defining the cellular processes regulating angiogenesis.