Uraemic and 1-alpha-hydroxycholecalciferol induced aortic lesions.

Aortic alterations in uraemic rats were studied ultrastructurally. The main changes consisted of degeneration and necrosis of smooth muscle cells and occurrence of extracellular calcifications. These alterations were aggravated when 1-alpha-hydroxycholecalciferol (1-alpha-OH-D3) was given in a slightly hypercalcaemic dose. Parathyroidectomy prevented, to some degree, the development of ultrastructurally demonstrable changes; this effect was abolished when 1-alpha-OH-D3 was given. The influence of 1-alpha-OH-D3 and parathyroidectomy on the aorta in uraemia was not solely a function of their effect on the serum calcium X phosphate product. Bodies composed of concentrically arranged (target-like) ring formations (1,200-6,000 A in diameter), possibly originating from degenerated smooth myocytes, were observed in the aortae of uraemic rats. These bodies may represent the matrix for initial calcification in the ground substance. The calcium salt deposits in the target-like bodies disappears when the tissues are stored in glutaraldehyde solutions for a long period of time. Calcifications were normally only found extracellularly, and it is proposed that the target-like bodies may locally initiate the calcification process.