Studies are presented in a patient with pseudohypoparathyroidism who showed a partial response to parathyroid extract. Resistance to the extract was observed after its short term administration for the 4th time. Serum from the patient contained antibodies of the γG globulin class which bound 125I labeled bovine parathyroid hormone. Prior incubation of parathyroid hormone with the serum prevented the activation in vitro of adenylate cyclase from pork renal cortex. The antibodies were directed primarily toward the C terminal portion of the molecule. Thus, clinical resistance to parathyroid hormone is attributed to specific antibodies.
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