Adrenal regeneration hypertension prevented by thyroidectomy: a quantitative ultrastructural study of the regenerating adrenal cortex.

Thyroparathyroidectomy (TPX) prevents adrenal regeneration hypertension (ARH) in female rats and concomitantly inhibits regeneration of the adrenal cortex. Removal of the thyroid gland plays the major role in preventing ARH inasmuch as parathyroidectomized adrenal-enucleated (PX-AE) rats became hypertensive, whereas thyroparathyroidectomized adrenal-enucleated rats (TPX-AE + PT) did not. Inhibition of adrenocortical regneration by TPX is reflected by a significant decrease in adrenal weight, volume of cortical parenchymal tissue per gland, and average cell volume at three weeks, compared with the regenerating adrenal gland in adrenal-enucleated thyroid-parathyroid-intact (AE) rats. Mitochondria in TPX-AE rats resembled closely those from zona fasciculata cells of a normal adrenal gland; stereologic techniques for electron microscopic examination confirmed that mitochondrial volume/cell and surface area of total mitochondrial membranes/cell (outer/inner membranes plus cristae) of adrenocortical cells from TPX-AE rats did not differ significantly from those of AE animals. The surface area of mitochondrial cristae of TPX-AE rats, however, was significantly greater than that of AE rats, whereas the surface area of the inner/outer mitochondrial membrane of the TPX-AE group was decreased significantly as compared with that of the AE group. The diameter of mitochondria in TPX-AE rats was larger than in the AE group, although the number of mitochondria/cell was significantly less in TPX-AE rats than in AE rats. Although TPX had no significant effect on the levels of DOC or corticosterone in the serum of quiescent AE rats as compared with TPX-AE rats, the rise in DOC in the serum after ether stress was blunted in the TPX-AE group as compared with that in the AE group. The rise in corticosterone in the TPX-AE group was comparable to that of the AE animals. Thus, partial inhibition of adrenal regeneration in TPX-AE rats in combination with a blunted rise in DOC levels in response to stress may well contribute to the prevention of ARH.