Decreased Adenosine Triphosphatase Activity in the Absence of Adrenocorticosteroids

Abstract

\s=b\ Changes in adenosine triphosphatase activity and cellular integrity of rat innerear tissues were observed after removal of adrenal steroids via bilateral adrenalectomy. Statistical significance of total and magnesium ion-dependent adenosine triphosphatase activities of the stria vascularis, spiral ligament, and ampullar dark cells from adrenalectomized animals was detected when compared with those of controls as demonstrated by fluorometric microassay. Although there was a similar reduction of activity in utricular dark-cell tissues, no significant difference between the treated and control animals was observed. An increase of intercellular space and a decrease in basolateral infoldings of cells of the stria vascularis and dark cell regions of adrenalectomized animals were observed. Such data collectively provide indirect evidence that adrenal steroids are involved in the cellular regulation of inner-ear tissues that are concerned with fluid and ionic microhomeostasis.(Arch Otolaryngol Head Neck Surg. 1989;115:817-821) Adenosine triphosphatase (ATPase) has been demonstrated to be a vital enzyme in active transport mech¬ anisms of cells involved in ionic and fluid homeostasis throughout the body. Despite localization and quantitation of inner-ear ATPase by numerous investigators,18 regulation of such in¬ ner-ear activity remains an enigma. Recently, significant change in the sodium -potassium -ATPase (Na --ATPase) activity of selected inner-ear tissues was reported after bilateral adrenalectomy.9 Such data suggested that inner-ear microhomeostasis may be partially influenced by the effect of adrenal steroids on inner-ear ATPase activity.To define further inner-ear ATPase regulation by adrenal steroids, total and magnesium ion (Mg++)-dependent ATPase activities and cellular mor¬ phology of selected inner-ear tissues were determined. The hypothesis tested was that changes in serum levels of adrenal steroids can affect ATPases (eg, calcium and magnesium ions) other than Na-K-ATPase and can affect cellular features of certain inner-ear tissues, leading to fluid and ionic imbalance that may be associated with patients with inner-ear dysfunc¬ tion.The rationale of this investigation was based on the fact that the adrenal gland secretes mineralocorticoids (eg, aldosterone) and glucocorticoids (eg, Cortisol in humans and corticosterone in rats) (Fig 1). Mineralocorticoids af¬ fect ion-transporting epithelial cells by activating the transport of Na+ from the apical side to the vascular side and transport of K+ from the vas¬ cular side to the apical epithelial side. Glucocorticoids increase blood glucose concentration as well as affecting both plasma and fat metabolism. Both min¬ eralocorticoids and glucocorticoids are known to bind to receptor proteins and increase Na-K-ATPase activity.The approach used in this study was to remove endogenous steroids by bi¬ lateral adrenalectomy, thereby creat¬ ing a condition in which inner-ear en¬ zymatic activity and morphological changes could be examined in the ab¬ sence ...

Distribution of glucocorticoid receptors and 11 beta-hydroxysteroid dehydrogenase isoforms in the rat inner ear

“…et al, 1998). Studies in rat have shown a positive correlation between serum levels of corticosteroid (glucocorticoid and mineralocorticoid) hormones and the amount of Na + ,K + -ATPase in the inner ear Rarey et al, 1989). Low levels of GRs in immunostaining and ELISA were observed in the previously studies in the SV (Rarey and Curtis, 1996;Zuo et al, 1995).…”

Cochlear ultrastructure in two-phase endolymphatic hydrops in the guinea-pig

“…In recent experiments, a relationship between circulating adrenal steroids and Na/K-ATPase activity in the inner ear was observed [10,11]. Emotional stress leads to the activation of neuroendocrine effector systems, including the production of adrenal steroids such as aldosterone, and could thus increase the production of endolymph.…”

How Useful Is Corticosteroid Treatment in Cochlear Disorders?

“…Adenosine triphosphatase activity was decreased in the stria vascularis, spiral ligament and ampullar dark cells, but not in utricular dark-cell tissues in adrenalectomized rats [141].…”

“…The morphological integrity of the cellular architecture of the stria vascularis [141][142][143] and the ampullar dark cells [141,144,145] is dependent on an adequate plasma corticosteroid level in rats. When diet-induced mineralocorticoid deficiency is substituted with aldosterone, the number of Na + ,K( + )-ATPase sites in the lateral cochlear wall and in the ampullae of the semicircular canal is increased in guinea pigs [85].…”