The Aortic Content of Glycosaminoglycans, Hydroxyproline and Calcium in Experimental Uraemia with Special Reference to Parathyroidectomy and Vitamin-D Treatment

Abstract

The contents of the various glycosaminoglycan (GAG) fractions, hydroxy proline and calcium in the thoracic aorta from the rat were studied. The effect on these contents of induced uraemia (3/4 kidney resection) combined with parathyroidectomy and/or 1-α-hydroxycholecalciferol (1-α-OH-D₃) treatment was evaluated. Confirming earlier results increased levels of GAGs (predominately of chondroitin and dermatan sulphate) were found in the aortae of uraemic rats. The present study showed that parathyroidectomy or treatment with 1-α-OH-D₃ did not significantly further alter the aortic content of GAGs in uraemic rats. Arteriosclerotic changes (calcifying medial necrosis) were only found in non-parathyroidectomized uraemic rats given 1-α-OH-D₃. The aorta from these rats had a lower total content of GAGs, mainly due to a decrease in hyaluronic acid, than that from uraemic rats without calcifications. The aortic content of calcium was lowest in uraemic parathyroidectomized rats. Treatment with 1-α-OH-D₃ increased this content, which was augmented 100-200-fold when calcifications were present. No correlation between the aortic contents of calcium and GAGs was found. There was a statistically significant correlation between the aortic content of calcium and the serum calcium × phosphate product. A significantly lower content of hydroxyproline was found in uraemic non-parathyroidectomized rats given 1-α-OH-D₃, especially in those with arteriosclerosis. It is concluded that the changes in GAGs and hydroxyproline in uraemia are problably associated with metabolic disturbances in the smooth muscle myocytes of the aortic wall. Treatment with 1-α-OH-D₃ in uraemic rats had only a minor effect on the content of GAGs, whereas the content of hydroxyproline decreased in uraemic rats given 1-α-OH-D₃. No correlation was found between the development of medial calcifications and the content of GAGs in the aorta.