THYROID-C CELLS OF MIDDLE-AGED RATS TREATED WITH ESTRADIOL OR CALCIUM

The structure and function of C cells of middle-aged female rats (14-m onths old) treated with estradiol dipropionate (EDP), calcium (Ca) or a combination of EDP+Ca were studied. A stereological method was used to determine the volume of calcitonin (CT)-immunoreactive C cells and their nuclei, and the relative volume density and mean number of the C cells per section were calculated. Serum levels of CT, osteocalcin, p arathyroid hormone (PTH), and beta-estradiol were also measured. A sig nificant decrease in body weight of the rats treated with EDP or EDP+C a was observed. These treatments led to a significant decrease in cell ular and nuclear volumes, relative volume density, and mean number of C cells per section, in comparison with the corresponding controls. A reduction of the serum level of CT, PTH, and osteocalcin was also reco rded in EDP-and EDP+Ca-treated animals. No statistically significant d ifferences between Ca- and vehicle-injected rats, with regard to all m orphometric C cell parameters and biochemical values determined, were seen. However, a conspicuous degranulation of the C cells and decrease d immunoreactivity for CT in the Ca-receiving group, which could be in terpreted as the signs of increased activity of these cells, were noti ced. This effect of Ca was also observed in rats injected with EDP and Ca in combination, when the inhibitory effect of EDP on C cell functi on was less noticeable than in the group treated with EDP alone.