Parathyroid gland function in the uremic rabbit.

Abstract

Rabbits with renal failure have been reported to be hypercalcemic and to have decreased parathyroid hormone (PTH) concentrations. Thus, it would seem that uremic rabbits are resistant to secondary hyperparathyroidism (HPT). The work reported here was designed to investigate parathyroid gland function in uremic rabbits and the effect of diets with different calcium (Ca) and phosphorus (P) content. The relationship between PTH and ionized calcium (Ca2+), parathyroid gland size and parathyroid cell cycle were studied in three groups of rabbits: Group I, rabbits with normal renal function on a standard diet (Ca = 1.2%, P = 0.6%); Group II, partially nephrectomized rabbits on a standard diet; and Group III, partially nephrectomized rabbits on a low Ca (0.6%)-high P (1.2%) diet. Group I rabbits had baseline Ca2+ = 1.71 +/- 0.05 mmol/l and PTH = 26.9 +/- 3.2 pg/ml. During hypo- and hypercalcemic stimulation PTH reached maximal values (PTHmax) of 94.4 +/- 5.5 pg/ml and minimal concentrations (PTHmin) of 3.2 +/- 0.2 pg/ml. Rabbits from Group II were hypercalcemic (baseline Ca2+ = 2.03 +/- 0.06 mmol/l) and had very low PTH levels (1.7 +/- 0.5 pg/ml); however, they reached a PTHmax that was similar to Group I, 92 +/- 8.7 pg/ml. Group III rabbits were hypocalcemic (baseline Ca2+ = 1.22 +/- 0.08 mmol/l) and had very high basal PTH levels (739 +/- 155 pg/ml). Their PTHmax and PTHmin were 801 +/- 169.4 pg/ml and 102.2 +/- 22.2 pg/ml, respectively. Both parathyroid gland size and parathyroid cell proliferation were increased in Group III. In conclusion, our results show that the Ca and P content of the diet markedly influence PTH secretion in the uremic rabbit and that when placed on a low Ca-high P diet uremic rabbits develop secondary HPT.