VALIDATION AND APPLICATION OF AN IMMUNORADIOMETRIC ASSAY FOR THE DETERMINATION OF HUMAN PARATHYROID-HORMONE FRAGMENT-1-34 IN DOG PLASMA FOLLOWING SUBCUTANEOUS AND INTRAVENOUS ADMINISTRATION

A method for the measurement of human parathyroid hormone fragment 1-3 4 (PTH1-34) in dog plasma was developed by modification of a commercia lly available immunodiometric assay (IRMA) designed for the determinat ion of rat PTH1-34 in serum. Major modifications were made to the assa y in order to circumvent significant problems encountered during the v alidation of the IRMA. PTH1-34 was found to be highly unstable in both rat serum and dog serum and plasma at room temperature, in contrast t o literature reports. The addition of a protease inhibitor cocktail to serum or plasma samples was necessary to prevent in-vitro proteolytic degradation of human PTH1-34 prior to analysis. Additionally, plasma was chosen over serum as the sample matrix to expedite the separation of samples from cells, minimizing proteolytic degradation prior to the addition of cocktail. Finally, the reported 100% cross-reactivity bet ween rat and human PTH1-34 was found to be only 65%; therefore, a huma n PTH1-34 standard was substituted for the rat standard. These modific ations allowed the accurate measurement of human PTH1-34 in plasma obt ained from dogs dosed intrevenously and subcutaneously with human PTH1 -34 using a commercially available kit.