Transforming growth factor beta (TGF-B) stimulation of angiogenesis: an electron microscopic study.

The object of this study was to examine the initiation and pattern of corneal angiogenesis stimulated by transforming growth factor beta (TGF-B) using scanning electron microscopy (SEM) of vascular corrosion casts and transmission electron microscopy (TEM). Fifty nanograms of TGF-B was combined with the slow release polymer Hydron and implanted in the rabbit cornea as an assay for angiogenic activity. Two and 7 days after implantation, the corneas were removed for TEM. At the same time intervals the limbal vasculature was filled with Mercox, an acrylic monomer. After the Mercox hardened, the tissue was digested with alternating immersions in 40% KOH and distilled water. The resulting casts were air-dried, sputter coated with gold and viewed with the scanning electron microscope. TEM revealed that 2 days after implantation, TGF-B elicited an influx of a vast number of inflammatory cells, which at two days were predominantly neutrophils. By 7 days the inflammation had subsided and typical capillaries were seen between the collagenous laminae of the normally avascular corneal stroma. SEM of vascular corrosion casts showed evidence of margination/diapedesis of leukocytes from the limbal venules 2 days post-implantation. In addition, the casts from the 7 day time point showed that new vessels arose solely from limbal venules.