Ouabain production by cultured adrenal cells.

Abstract

The adrenal cortex releases a sodium pump inhibitor. The present studies tested whether this material was endogenous and identical to ouabain by 1) studying the production of ouabain in long term cultures of adrenocortical cells, 2) seeking evidence that ouabain might be taken up from exogenous sources by adrenocortical cells, 3) examining the release of adrenocortical cells loaded with exogenous ouabain, 4) attempting to stimulate ouabain steroidogenesis in cultured adrenocortical cells, and 5) performing further chemical analysis on ouabain immunoreactivity released by cultured adrenocortical cells. Our results indicate that ouabain immunoreactivity is present in conditioned medium from both murine Y-1 adrenocortical cultures and primary bovine adrenocortical cell (BAC) cultures. We also found that BACs bind and internalize [3H]ouabain. Bound [3H]ouabain is released from BACs by both receptor dissociation and cytoplasmic release of internalized [3H]ouabain. Only one isoform of membrane sodium, potassium-adenosine triphosphatase, alpha 1, was expressed in the adrenal. Authentic ouabain was not metabolized during membrane binding or while present intracellularly. Stimulation of steroidogenesis in Y-1 and BAC with 22R-hydroxycholesterol and 25-hydroxycholesterol was performed and confirmed increased steroidogenesis; however, there was no effect on ouabain immunoreactivity content or release. Comparison of the ouabain binding density in cultured BAC, hepatoma cells, and 3T3 fibroblasts indicated that adrenocortical cells have a high ouabain-binding capacity. HPLC studies of the ouabain immunoreactivity released by bovine adrenocortical cells indicated that essentially no authentic ouabain was secreted. The present studies confirm that both BAC and Y-1 cultures release a ouabain-like material that differs in structure from authentic plant ouabain and is not a product of cholesterol side-chain cleavage.

Ouabain Enhances Cell-Cell Adhesion Mediated by β1 Subunits of the Na+,K+-ATPase in CHO Fibroblasts

“…It was suggested that Ouabain is a hormone when Hamlyn and Mathews demonstrated the presence in plasma of a substance similar to ouabain in plants [22,37]. Thereafter, it was shown that endogenous ouabain is synthesized and secreted by the hypothalamus [38,39] and the adrenocortical gland [40,41,42]. The status of ouabain as a hormone was strengthened upon the discovery of increased concentrations in plasma during exercise, ingesting salty foods, and in pathological conditions such as arterial hypertension and myocardial infarction [43,44,45,46,47,48].…”

Markedly divergent effects of Ouabain on a Temozolomide-resistant (T98G) vs. a Temozolomide-sensitive (LN229) Glioblastoma cell line

“…The Cardiotonic Steroids (CTS) constitute a family of steroid hormones which decades ago were discovered in plants e.g., Ouabain from an African tree (Acokanthera ouabaio). It is nowadays established that Ouabain is synthesized and released mainly in the adrenal gland as demonstrated in different species [ 22 – 24 ]. Moreover it was shown that, like other “stress hormones”, they are part of the Hypothalamic–Pituitary–Adrenal axis and stimulated by the adrenocorticotropic hormone (ACTH) and Angiotensin II [ 25 , 26 ].…”

Research Progress in Pharmacological Activities and Applications of Cardiotonic Steroids

“…Currently, the clinical preparations include digitoxin, digoxin, lantoside C and strophanthin K. Endogenous CTS are endogenous digitalis-like factors (EDLF) found in mammalian tissues and body fluids (including the brain, adrenal gland, plasma, urine, and placenta, etc. ), such as ouabain-like substances found in human plasma and adrenal glands, digitalis-like substances found in human urine and placenta, ouabain-like substances extracted from bovine hypothalamus (Goto et al, 1990;Hamlyn et al, 1991;Tymiak et al, 1993;Doris et al, 1996;Ma et al, 2012). Whether they are endogenous or exogenous, the basic structure of CTS determines that they have similar effects, and different modification groups provide them with rich pharmacological activities.…”