Human parathyroid autografts: Comparison of function in vivo and in vitro

Suppressibility of parathyroid function by calcium was compared in vivo and in vitro for five patients with parathyroid autografts to the forearm. Suppressibility of parathyroid secretion was studied in vitro with dispersed parathyroid cells and in vivo by determining nephrogenous cAMP (NcAMP) excretion and parathyroid hormone (PTH) concentration in the antecubital vein. In four patients with primary parathyroid hyperplasia, a graded calcium infusion caused progressive inhibition of NcAMP and PTH release from the autograft. Maximal inhibition of 90 to >95% and 60 to >95%, respectively, was achieved with total calcium concentrations that reached maxima of 2.65-3.1 mM. PTH release from dispersed parathyroid cells of these patients was suppressed 70-80% by ionized calcium concentrations of 1.5-2.0 mM. A single patient with a transplanted adenoma showed a 17-39% suppression of NcAMP and a 20-60% inhibition of antecubital venous PTH in two separate calcium infusions, as well as a 20-30% inhibition by calcium of PTH release from dispersed parathyroid cells in vitro. The present results indicate a close correlation between PTH in the venous effluent from parathyroid autografts and NcAMP. Suppression of parathyroid function by elevated calcium concentration was very similar in vivo and in vitro, suggesting further that dispersed human parathyroid cells provide a valid representation of parathyroid suppressibility in vivo. Taken in conjunction with our previous studies with dispersed parathyroid cells in vitro and in patients given calcium infusions before parathyroidectomy, these studies are consistent with distinct calcium sensitivity in parathyroid adenoma vs. primary hyperplasia.