Bioassay of Parathyroid Hormone in Vitro with a Stable Preparation of Adenyl Cyclase from Rat Kidney

Abstract

A bioassay for parathyroid hormone in vitro was developed based upon the activation of adenyl cyclase from the renal cortex of the rat. Preparation of the enzyme in 0.05M Tris-HCl, pH 7.4, containing 10% v/v dimethylsulfoxide allowed storage in liquid nitrogen for periods in excess of 30 days without significant loss of sensitivity to parathyroid hormone or fluoride. The assay was sensitive to as little as 0.14 USP U of parathyroid hormone, and showed a log-linear dose response over the range of 0.14– 1.13 USP U of hormone. The average index of precision in a series of 23 assays was 0.083. Theassay was highly specific for parathyroid hormone and showed appropriate increments in potency for hormone preparations at consecutive stages of purification. Results with the adenyl cyclase method in vitro were similar to those obtained with a standard bioassay in vivo. There was no significant interference from other hormones and proteins, including nonhormonal contaminants found in crude parathyroid extracts. The adenyl cyclase method was simple to carry out and highly reproducible. (Endocrinology85: 801, 1969)