Alterations of thyroid parafollicular cell organization in aged rats neonatally treated with estradiol.

Cellular and subcellular organization of parafollicular cells of aged male Wistar rats (180- and 365-day-old), neonatally (3rd day) treated with a single dose (1 mg) of oestradiol-dipropionate (OeDP), were studied. Based on argyrophil properties of parafollicular cells in control and treated group, two morphometrically distinct cell types were observed (under and over 50 microns 2 of cell area), reflecting distinct functional status of the same cell type. The first signs of hyperplastic changes in parafollicular cells were observed in 180-day-old rats and they were more severe in 365-day-old animals. Morphometric averages for the area of parafollicular cells and nuclei, as well as for the cell number in estradiol-treated animals were higher than in the controls, but these differences were statistically insignificant. However, subcellular organization of parafollicular cells showed that besides the cells with clearly visible characteristics such as control hyperplastic cells, there were parafollicular cells with progressively more abnormalities expressed as myelin-like figures, cytoplasmic cribriform structures and dilated endoplasmic reticulum (ER), demonstrating long-lasting effects of neonatally applied estradiol.