Morphology of early large vessel lesions in experimental hypertension.

Lesions of the aorta and large muscular arteries were examined in experimental hypertension of the albino rat. In contradiction to the published data the earliest hypertensive lesion was a small artery type subendothelial fibrinoid and necrosis of single smooth muscle cells in the media and not an intimal thickening. In the large vessels such changes developed only after long periods of hypertension. No lesion corresponding to the media fibrinoid of small vessels was found in the large muscular vessels or in the aorta, owing apparently to inhibition of a greater penetration of plasma by the elastic fibres. This barrier role may in addition account for the absence of perivascular granulation around the aorta. In a later stage of the process, macrophages appeared in the subendothelial fibrinoid, phagocytosed it, and gave rise to intimal proliferation analogous to the intimal thickening in small vessels.