Decreased plasma calcitonin response to a calcium clamp in primary hyperparathyroidism

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Abstract
To preoperatively evaluate the Ca induced plasma calcitonin (CT) response in patients with mild primary hyperparathyroidism (PHPT), 7 postmenopausal (PM) females with PHPT and 14 PM healthy subjects underwent a 2 h Ca infusion. The infusions were performed by means of the Ca clamp technique to obtain an identical Ca stimulus in all subjects. Immunoreactive calcitonin (iCT) was determined by means of a sensitive RIA [radioimmunoassay] utilizing rabbit antibodies directed against the carboxy-terminal amino acid sequence of the CT molecule. All patients with PHPT had normal basal plasma iCT levels: 10 .+-. 5 pg-eq/ml (mean .+-. SD) as a group and not different from the control group: 13 .+-. 5 pg-eq/ml. In the control group significantly increased plasma iCT was seen at 30, 60, 90 and 120 min in contrast to that of the PHPT group where a blunted response was observed. A diminished CT reserve in these patients which may imply an impaired defence against the PTH [parathyroid hormone] mediated bone resorption seen in patients with PHPT was indicated.