Effect of thyroparathyroidectomy (TPX) on the zona reticularis: A quantitative ultrastructural study

Abstract

Atrophy of zona reticularis cells was observed two weeks after surgical thyroparathyroidectomy (TPX). Quantitative morphological techniques for electron microscopy showed significant decreases in the volume of cytoplasm, nucleus, mitochondria, smooth endoplasmic reticulum and lipid droplets in the zona reticularis of TPX rats. In addition, many mitochnodria contained lipid droplets, some of which occupied virtually the entire matrix of mitochondria. The volume per cell of mitochondria with these inclusions increased significantly after TPX. The lipid droplets may well arise from cytoplasmic droplets by increased transport or reduced metabolism of cholesterol, or by direct incorporation of droplets into the mitochondrial matrix. The serum corticosterone level of TPX rats sacrificed under quiescent conditions did not differ significantly from that of controls. Hypothyroidism induced a significant increase in the volume of peroxisomes per cell in TPX animals which may be related to changes in lipid metabolism or transport.

Atrophy of the zona fasciculata in the adrenal cortex of thyroparathyroidectomized rats: A quantitative study

“…I t is clear that TPX exerts its major effect on the zona fasciculata, which suggests that the three cortical zones react differently to TPX. Difference in cortical reactivity is also supported by presence of numerous lipid inclusions in the zona reticularis at 2 weeks after w w co TPX (Conran and Nickerson, 1979), but only an occasional mitochondrion with a lipid droplet in the matrix was observed in the region of the zona fasciculata bordering the zona reticularis in the present study a t 2 and 7 weeks. A significant increase in peroxisomes was present in the zona reticularis at 2 weeks (Conran and Nickerson, 1979), although the volume of peroxisomes was not counted in zona fasciculata cells in the present study.…”

“…In contrast, surgical TPX obviates the necessity for drug treatment and allows complete removal of the gland, although the parathyroid is removed as well. Nonetheless, our d a t a indicate t h a t parathyroid ablation has no effect on the ultrastructure of zona-fasciculata cells, inasmuch as we found no significant difference in ultrastructure between intact and parathyroidectomized rats except for a decrease in lipid-droplet volume in the zona fasciculata of PX rats and in zona reticularis of PX animals (unpublished observation; Conran and Nickerson, 1979). This study supports the view that the changes observed in TPX rats are attributable principally to the hypothyroid state and are not the result of removing the parathyroid glands.…”

“…A drawback in interpreting some of the previous studies, which could explain in part the different results, is that antithyroid agents may have a direct effect on the adrenal gland (Money, 1955;Pittman, 1971; Moore and Callas, 1975). Thyroparathyroidectomy obviates the use of such agents; recently, we reported a decrease in relative weight of the adrenal gland in rats made hypothyroid by surgical thyroparathyroidectomy (TPX; Conran and Nickerson, 1979).…”

Validation of cell volume determination for stereological studies of adrenocortical cells: Comparison of values from semifine sections with those of dissociated zona fasciculata cells

“…Among possible reference systems are allometric parameters, cell mass, organ volume, or cell volume. The latter has been employed in a number of stereological studies of the adrenal cortex (Nussdorfer, 1970;Rohr et al, 1976;Conran and Nickerson, 1979).…”