It is uncertain at present whether a change in the rate of apoptosis can also contribute to parathyroid tissue hyperplasia . One research group examined this issue in rats with short-term renal failure (5 days) and failed to detect apoptosis in hyperplastic parathyroid glands . However, this failure could be due to lack of sensitivity of the employed methods.
Negative findings in rats, with no identifiable apoptotic figures at all in parathyroid glands , contrast with more recent positive observations in rats by others, either spontaneously or after parenteral of intraparathyroidal injection of active vitamin D compounds . and with personal observations of significant apoptotic figures in hyperplastic parathyroid glands removed from uremic, severely hyperparathyroid patients during surgery . In our study in humans, we found approximately ten times higher apoptotic cell numbers in uremic patients than in normal parathyroid tissue, using the Tunel method (Figure 12) . Of note, the uremic state appears to stimulate apoptosis in other cell types as well such as circulating monocytes , possibly via the well-known increase of cytosolic Ca2+ which has been observed in a variety of cell types in renal failure , and also possibly via the noxious effect of bioincompatible dialysis membranes used for renal replacement therapy . If confirmed by others, the observed enhancement of parathyroid tissue apoptosis could compensate, at least in part, the increase in parathyroid cell proliferation observed in 2° uremic hyperparathyroidism.
