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The Metatarsal Cytochemical Bioassay of Parathyroid Hormone: Validation, Specificity, and Application to the Study of Pseudohypoparathyroidism Type I^*

JEREMY N. BRADBEER, JANE DUNHAM, JAN A. FISCHER, CHARLES NAGANT DE DEUXCHAISNES and NIGEL LOVERIDGE

Division of Cellular Biology (J.N.B., J.D., N.L.), Kennedy Institute of Rheumatology London W6 7DW, United Kingdom
Departments of Orthopaedic Surgery and Medicine (J.A.F.), University of Zurich Switzerland
Department of Rheumatology (C.N.de D.), Louvain University Brussels, Belgium
Bone Growth and Metabolism Unit (N.L.), Rowett Research Institute Aberdeen AB2 9SB, United Kingdom

Address all correspondence and requests for reprints to: Dr. Nigel Loveridge, Rowett Research Institute, Greenburn Road, Aberdeen, AB2 9SB, United Kingdom.

The most sensitive method for assaying the bioactivity of PTH in unextracted plasma is the renal cytochemical bioassay. However, PTH acts on bone as well as kidney and clinical studies have suggested that the actions of circulating PTH level may be different at the two sites. We developed cytochemical bioassay for PTH based on the stimulation of glucose 6-phosphate dehydrogenase activity in the hypertrophic chondrocytes of the growth plate and the osteoblasts lining the metaphyseal trabeculae of rat metatarsal bones. The index of precision was 0.14 ± 0.02 (SE) and the interassay variation was 31%. With this assay, plasma bioactive PTH levels in normal subjects and patients with primary hyperparathyroidism ranged from 0.5–18 ng/L and from 27–850 ng/L, respectively. Studies of patients with pseudohypoparathyroidism type I indicated that plasma PTH bioactivity in such patients is greater in the metatarsal bioassay than in the renal bioassay; no such differences were found in normal subjects or patients with primary hyperparathyroidism.

^* This study was supported by Action Research for the Crippled Child (S/P/1590), the Arthritis and Rheumatism Council for Research, and The Swiss National Science Foundation Grant 3.957-0.84. This study was presented in part at the 9th International Conference on Calcium-Regulating Hormones and Bone Metabolism, Nice, France; 1986 and the 97th Annual Meeting of The Endocrine Society, Baltimore, MD, 1985.

Present address: JNB-Clinical Research Centre, Harrow, Middlesex, HA1 3UJ, UK.

Received February 18, 1988.

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