An Effect of Parathyroid Hormone on the Epiphyseal Plate and Osteoblasts: Studies Towards a Cytochemical Bioassay

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Abstract
There are reports of an apparent dissociation between the responses of kidney and bone to parathyroid hormone (PTH): certain fragments or analogues have been shown to have differential activity in these two tissues. Consequently, cytochemical bioassay techniques have been applied to the development of an assay for PTH using the epiphyseal plate of the rat metatarsal as the target organ. Glucose 6-phosphate dehydrogenase activity in the zone of hypertrophic cartilage is stimulated in a log-linear fashion with increasing concentrations of parathyroid hormone over the range 0.001–1.0 pg/ml. A parallel response was found in the osteoblasts of the metaphysis. Measurements of a normal and a hyperparathyroid plasma sample showed good parallelism to the standard graph and good discrimination. Addition of a PTH - specific antibody inhibited both the effect of the standard preparation of the hormone, and the response induced by dilutions of a normal plasma.