Collagen fibril diameters in arteries of mice. A comparison of manual and computer-aided morphometric analyses.

Arteries of mice were studied by a silver impregnation technique, by the Picrosirius-polarization method and by transmission electron microscopy. The histochemical results obtained coincided with the electron-microscopic observations in showing the presence of two distinct collagen populations, segregated into different compartments of each artery. The fibrous component of the tunica media was comprised of reticulin fibers, which displayed a distinct argyrophilia when studied by means of the silver impregnation technique, and showed up as thin, weakly birefringent, greenish fibers when examined with the aid of the Picrosirius-polarization method. In addition, the electron-microscopic studies disclosed the presence of thin collagen fibrils in the tunica media, contrasting with the thicker fibrils that could be localized ultrastructurally to the tunica adventitia where nonargyrophil, coarse collagen fibers had been characterized by the histochemical methods used. In this respect, collagen distribution in arteries of mice is very similar to the pattern that was consistently observed in the other species studied, which argues in favor of the existence of a uniform structural pattern of collagen distribution that is a general phenomenon in vertebrate arteries. Experimental results comparing the traditional method and the computer-aided measurement of collagen fibril diameters showed that the system provides results equivalent to those produced by manual execution. In addition, the advantage in speed of the computer-aided method should prove useful in complicated studies where numerous structures are involved.