Influence of the Parathyroids on Plasma Hydroxyproline Levels

Abstract

Plasma levels of hydroxypro line were studied in rats subjected to dietary limitation, parathyroidectomy, nephrectomy and combinations of these conditions. Total hydroxyproline levels were determined on hydrolyzed samples and compared with the amounts observed without hydrolysis in aliquots of the same samples. Parathyroidectomy consistently lowered plasma hydroxyproline levels, although the changes were minimal in hydrolyzed plasma samples taken from animals maintained on normal diets. Nephrectomy lowered the values of nonhydrolyzed plasma samples, but increased markedly the total hydroxyproline content as determined by hydrolysis. It is suggested that one source of plasma hydroxyproline was collagen which was broken down as a result of parathyroid-bone interactions in the process of maintaining a constant plasma calcium level. Nephrectomy, which increases endogenous parathyroid activity, appears to increase the breakdown of bone collagen, transferring the hydroxyproline residues to plasma in a bound form.