The effects of hyperthyroidism on the fine structure of the zona fasciculata of the rat adrenal cortex

Abstract

Chronic hyperthyroidism was induced in radiothyroidectomized and surgically thyroidectomized adult male rats by feeding a diet of 0 3 4 . 4 % desiccated thyroid for four to ten week periods. Short term hyperthyroidism was induced in intact rats by the intraperitoneal injection of 250 pg/day of sodium levothyroxine for ten days. Adrenal glands were fixed by perfusion with 3% phosphate buffered glutaraldehyde and post-fixed in 1 % osmium tetroxide. The zona fasciculata of the adrenal glands from experimental and control animals was examined in the electron microscope. Drastic mitochondrial alterations characterized the zona fasciculata of hyperthyroid rats. Initially, mitochondria became more nearly round and contained increased numbers of paracrystalline tubular inclusions of the type described by Kjaerheim ('67) and Wheatley ('68).In more altered states many mitochondria were filled with clusters of parallel tubular cristae of varying complexity which at times enveloped islands of mitochondrial matrix and fingers of cytoplasm which projected into the mitochondrion. Aggregations of numerous mitochondria occupied much of the cytoplasm of highly altered cells. Modifications of this nature have not been described following ACTH stimulation of the adrenal cortex. This raises the distinct possibility that thyroid effects on the adrenal cortex are not entirely ACTH mediated.Since the observations of Hoskins ('10) it has been known that the administration of thyroid material to animals results in the hypertrophy of their adrenal glands. Adrenocortical hypertrophy after treatment with thyroxine or desiccated thyroid has been demonstrated in the rat (Cohen, '35 Although reports on the effects and the mechanism of thyroid-adrenal interaction have often conflicted, there can now be little doubt that thyroid hormone does have an influence on the adrenal cortex. The alterations in histology and function reported by numerous investigators should almost certainly be accompanied by changes in ultrastructure; however, no ultrastructural studies in support of such a conclusion have been recorded to this date. The purpose of this paper, therefore, is to describe the effects of hyperthyroidism on the fine structure of the rat adrenal cortex and possibly to shed additional light on the mechanism of thyroid-adrenal relationships. Although all zones of the adrenal cortex were examined, observations described in this report are limited to the zona fasciculata. MATERIALS AND METHODSAnimals used in this experiment were Tex/SDD adult male albino rats weighing 250-300 gm at the onset of the experiment. Alteration in available thyroid secretion was achieved by surgical thyroidectomy or radiothyroidectomy followed by treatment with desiccated thyroid and by thyroxine administration to intact animals. Short term hyperthyroidism was produced in two intact animals by the intraperitoneal injection of 250 pg of sodium levothyroxine per day for ten days. These animals were sacrificed 24 hours after the last injection. Long term hyperthyroidi...

Experimentally-induced hyperthyroidism is associated with activation of the rat hypothalamic–pituitary–adrenal axis

“…However, symmetrical enlargement of the adrenals in the context of hypercortisolism has almost always been associated with physiological contexts in which there has been hyperstimulation of the adrenal cortex with ACTH, rather than with the context of a primary adrenal process (8,18,19). In light of our previous oCRH stimulation studies, this would suggest a central locus for the hyperthyroid-mediated hypercortisolism.…”

Effects of Short and Long Duration Hypothyroidism and Hyperthyroidism on the Plasma Adrenocorticotropin and Corticosterone Responses to Ovine Corticotropin-Releasing Hormone in Rats*

“…The significant reduction in adrenal weight seen in hypothyroid rats is also compatible with either primary or secondary adrenal insufficiency and is almost never seen in any other context (33). However, symmetrical enlargement of the adrenals in the context of hypercortisolism has almost always been associated with physiological contexts in which there has been hyperstimulation of the adrenal cortex with ACTH, rather than with the context of a primary adrenal process (33,35,36). Although we cannot definitively document the cause of the subtle adrenal insufficiency seen in our hypothyroid rats, this adrenal insufficiency does not seem to reflect the reduction in corticosterone clearance known to occur in hypothyroidism or the reduced CBG-binding capacity seen in the present study of hypothyroid rats.…”

Morphometric changes in the lungs of rats following adrenalectomy supplemented by desiccated thyroid

“…Similar effects have been reported following the administration of adrenal hormones (DeLemos et al, 1970;Kotas and Avery, 1971; Picken et al, 1974). Since effects of adrenal hormones on the thyroid gland (Solis-Cohen, 1897; Marine, 1930;Malendowicz and Filipiak, 1975), and of thyroid hormone on the adrenal glands (Hoskins, 1910;Steinetz and Beach, 1963;DAngelo and Grodin, 1964; Moore and Callas, 1972), are well established, consideration must be given to the possibility that the lung effects produced by thyroid administration may be mediated through activity of the adrenal cortex. To date, no studies have been reported investigating adrenal activity or thyroid-adrenal interactions influencing the thyroid-induced changes described in mature lung.…”