PARATHYROID-HORMONE AFTER ADENECTOMY FOR PRIMARY HYPERPARATHYROIDISM - A STUDY OF PEPTIDE-HORMONE ELIMINATION KINETICS IN HUMANS

The study of the elimination kinetics of peptide hormones in humans is limited, because determining hormone levels in different compartments is difficult. We calculated the elimination kinetics of intact PTH (1 -84) after adenoma removal in primary hyperparathyroidism, based on a 2-compartment model. In 12 patients, blood samples were drawn in short intervals preoperatively, during surgery, and up to 4 days postoperat ively. Plasma levels of PTH (1-84), calcium (Ca), and inorganic phosph ate were determined. PTH (1-84) levels remained constant before surger y and during adenoma preparation; 2.5 min after clamping of the adenom a's blood supply, PTH (1-84) decreased (34.9 +/- 4.8 vs. 23.3 +/- 2.9 pmol/L, mean +/- SEM, P < 0.001) and then reached a minimum of 0.96 +/ - 0.06 pmol/L at 5 h. The elimination half-lives for PTH (1-84) were 3 .43 +/- 0.1 min and 81.7 +/- 12.7 min. Ionized Ca started to decrease 30 min aft;er adenoma removal (1.58 +/- 0.04 vs. 1.56 +/- 0.04 pmol/L, P < 0.001). This decrease was paralleled by a decrease in total Ca. I norganic phosphate increased 24 h after adenoma removal. In conclusion , PTH (1-84) elimination after adenectomy is characterized by a rapid initial decrease and a subsequent prolonged period with a lower elimin ation rate. This elimination pattern may also apply to other human pep tide hormones.