Proliferative activity of the parathyroid cells in rats with secondary hyperparathyroidism

Proliferative kinetics of parathyroid cells in secondary hyperparathyroidism (HPT) are still unknown. We examined the histopathological changes and proliferative activity of parathyroid cells in spontaneously hypercholesterolemic (SHC) rats that exhibit secondary HPT and in normal Sprague Dawley (SD) rats from 3 weeks to 32 weeks of age. Proliferative activity [proliferating cell nuclear antigen(PCNA) labeling index], evaluated by means of immunohistochemical examination of PCNA, declined in SD rats with age from 10.8% at 3 weeks of age to 0.15% at 32 weeks of age. In SHC rats, a PCNA labeling index of 11.6% declined to 3.12% at 14 weeks of age and rebounded to 6.15% at 26 weeks of age. Parathyroid glands increased in size as determined by the maximum cross-sectional area, but in SHC rats, the increase was significantly greater, paralleling the progression of renal dysfunction, and at 32 weeks they were almost three times larger than in SD rats. Parathyroid hormone (PTH) levels in SHC rats also rose sharply after 20 weeks and reached 611 pg/ml at 32 weeks, while PTH in SD rats remained unchanged at approximately 110 pg/ml. This study showed that in the course of developing HPT in SHC rats, there is a large increase in the size of the parathyroid gland, a concomitant increase in PTH levels, and a PCNA labeling index that is higher than in normal SD rats.