The late vascular effects of radiation

In a previous report (Hopewell and Wright, 1970) attention was drawn to the similarities between the late effects of hypertension and of radiation on the vascular system. It was suggested that an important stage in the pathogenesis of latent hypertensive vascular damage was the appearance of irregularly spaced constrictions in arterioles (Byrom, 1963). It has been suggested that similar changes could occur in irradiated blood vessels (Hopewell, 1968; Hopewell and Wright, 1970), the constrictions being formed by clones of vessel wall elements, i.e. endothelial or muscle cells. These clones of cells originate from the irregularly spaced reproductively viable cells which remain after irradiation, and are stimulated into division as a result of cell loss which occurs as radiation damaged cells attempt to divide (Fig. 1). Changes similar to those predicted were later seen in the vessels of the irradiated mouse pinna (Lindop, Jones and Bakowska, 1970), an observation that we have also made in the small arterioles of the hamster cheek pouch, four to six months after irradiation with doses in the range 1,000–3,000 rads (Hopewell, 1971).