Effects of secretin on parathyroid hormone and calcium in normal subjects, patients with hyperparathyroidism and patients with gastrinoma

In vitro studies have demonstrated that secretin can stimulate the release of parathyroid hormone (PTH), but reports concerning its effects on PTH and calcium in vivo are contradictory. To examine this question further, a bolus injection of secretin (75 IU) was given to 12 normal subjects and 10 patients with primary hyperparathyroidism (HPT). Six of the patients had multiple endocrine neoplasia and five had endocrine pancreatic tumours (EPT). Three normocalcaemic patients with EPT were also included in the study. The mean serum gastrin level rose significantly (from 19 to 40 pmol/l, p less than 0.01) within 15 min of secretin injection in the normal subjects. HPT patients without EPT had a somewhat higher mean basal level of gastrin (39 pmol/l, p less than 0.05 compared with controls), but it did not increase significantly after the secretin bolus. In six EPT patients the gastrin concentrations rose by more than 300 pmol/l. Although secretin had a biological capacity to release gastrin, it had no discernible effects on either serum PTH or serum calcium in any of the groups studied. Nor were any changes in PTH or calcium observed when secretin was given as a continuous infusion (3 IU/kg/h) over 90 min. Thus, our data do not support the concept that secretin, in vivo, is a secretagogue of PTH.