Radioimmunoassay of Rat Parathyroid Hormone in Serum and Tissue Extracts

A sensitive radioimmunoassay, which will detect as little as 0.5 pg of purified bovine parathyroid hormone (PTH), has been developed to assay PTH in rat serum and rat parathyroid gland (PTG) extracts. Highly purified bovine PTH was used as standard and tracer. The antiserum was developed against partially purified bovine PTH in a chicken. The bound to free ratio (B/F) curves for varying concentrations of rat serum and PTG extracts were superimposable on B/F curves of the standard highly purified bovine PTH, indicating indistinguishable immunologic identities of these hormones as detected by this antiserum. PTH was detectable in all normal intact rats,but in no parathyroidectomized rats. Rats maintained on a low calcium (Ca) diet had serum PTH concentrations more than 3-fold those of rats fed a normal Ca diet. Nephrectomized rats had serum PTH concentrations almost 4-fold that of control rats, and parathyroid tissue PTH concentrations greater than 4-fold that of control rats. After an im injection of EDTA into normal rats, the serum PTHconcentration increased promptly as the serum Ca decreased. Both values then returned toward the baseline over the following 4 hr of observation. Utilization of this radioimmunoassay for rat PTHallows the rat to besed in further studies of factors regulating PTH secretion and metabolism. (Endocrinology94: 1644, 1974)