Reduced parathyroid functional mass after successful kidney transplantation

Background. Chronic uremia is responsible for secondary hyperparathyroidism (HPT II). Parathyroid secretion usually tends to normalize after kidney tr ansplantation (KT), but the parameters of the reversibility of HPT II remai n poorly defined, particularly the intrinsic mechanisms underlying the impr ovement of parathyroid function. Methods. The kinetic functional parameters of the ionized calcium (iCa)/par athormone (PTH) relationship curve were studied in 11 patients with mild to moderate HPT LI one and six months after successful KT. Hypercalcemia and hypocalcemia were induced, respectively, by CaCl2 and Na-2-ethylenediaminet etraacetic acid (Na-2-EDTA) infusions. Results. The mean glomerular filtration rate remained stable during follow- up. Basal PTH decreased from 195 +/- 54 pg/ml before KT to 70 +/- 12 pg/ml six months later (P < 0.005). During the tests, mean PTH levels decreased s ignificantly between the two measured times for all iCa levels, indicating an improved parathyroid function. An analysis of the kinetic parameters of the curves showed significant decreases of the mean maximal and minimal PTH levels, respectively, from 340 +/- 91 to 220 +/- 30 pg/ml (P = 0.03) and f rom 25 +/- 6 to 15 +/- 5 pg/ml (P = 0.005). On the other hand, no change wa s noted in the parathyroid-cell calcium-sensitivity parameters (slope, set point) assessed using two different approaches, either the entire curve or the limited calcium-mediated suppression curve. Conclusion. Improvement of the parathyroid function between the first and s ixth months post-KT seems mainly attributable to a reduction of the parathy roid functional mass.