Ouabain-Like Compound Changes Rapidly on Physical Exercise in Humans and Dogs

Abstract

Abstract-Ouabain, an inhibitor of the sodium pump, has been identified as a constituent of bovine adrenal glands. We were interested whether the release of this cardiotonic steroid is stimulated by physical exercise. Hence, athletes and healthy dogs were subjected to ergometry. Ouabain-like compound (OLC) was measured in venous blood by enzyme-linked immunosorbent assay as well as by 86 Rb ϩ uptake inhibition (as ouabain equivalents). OLC increased in venous blood of athletes after 15 minutes of ergometry from 2.5Ϯ0.5 to 86.0Ϯ27.2 nmol/L (nϭ51; PϽ0.001), as did the concentration of a circulating inhibitor of the sodium pump from 7.3Ϯ1.7 to 129.8Ϯ51 nmol/L (ouabain equivalents, PϽ0.05). Half-maximal increase in heart rate and systolic blood pressure occurred at 5.1Ϯ1.2 nmol/L and at 30Ϯ1 nmol/L OLC, respectively. On rest, OLC decreased in humans and dogs with a half-life of 3 to 5 minutes. In beagles exposed to moderate exercise on a treadmill for 13 minutes, levels of OLC increased 46-fold (from 3.7Ϯ0.8 to 166.9Ϯ91.8 nmol/L; nϭ6; PϽ0.005). This effect was suppressed when the dogs had been treated for 3 weeks with the ␤ 1 -adrenergic receptor blocker atenolol or the angiotensin-converting enzyme inhibitor benazepril. We conclude that OLC changes rapidly during exercise and is under the control of norepinephrine and angiotensin II. Key Words: angiotensin-converting enzyme inhibitor Ⅲ ␤-blocker Ⅲ circulation Ⅲ endogenous ouabain Ⅲ hypertension Ⅲ sodium pump hypertension O uabain or its isomer has been isolated from blood, adrenals, and hypothalamus 1-3 as one of the endogenous cardiac glycosides circulating in blood plasma. 4 Evidently, ouabain is synthesized in adrenal glands, 1,5,6 but it may also be accumulated there after resorption from the gut. 7 Bovine adrenocortical cells in tissue culture release ouabain on exposure to epinephrine, angiotensin II, or corticotropin. 1,6,8 Whether this in vitro finding translates into the in vivo situation is unclear. If so, physical exercise associated with the increase in epinephrine and norepinephrine should consequently increase endogenous ouabain. Previous studies showed ambiguous results. An increase 9 as well as a decrease of plasma concentrations of ouabain-like compounds (OLCs) 10,11 have been reported. Here, we investigated the effect of physical exercise on the endogenous ouabain plasma concentration in several experimental settings as well as the influence of ␤-blockade and angiotensin-converting enzyme (ACE) inhibition. Materials and MethodsAll chemicals were of the highest purity available. Anti-ouabain antibodies from sheep (CN2710) were from B.R.A.H.M.S. Arzneimittel (Dr A. Bergmann), Henningsdorf, Germany. The antibodies showed cross-reactivities with k-strophanthin 42%, ouabagenin 27%, dihydro-ouabain 0.3%, digitoxin 0.07%, and proscillaridin (Ͻ0.1%), and no cross-reaction (Ͻ0.01%) with strophanthidin, digoxin, digitoxigenin, oleandrin, marinobufagin, bufalin, cinobufagin, cinobufotalin, and 19 other steroid hormones. Human Patients and ControlsWritten inf...

Na/K-ATPase Tethers Phospholipase C and IP3 Receptor into a Calcium-regulatory Complex

“…Because there is sufficient evidence that ouabain and marinobufagenin are likely the endogenous cardiotonic steroids, our findings brings about an interesting question as to whether this mode of regulation is relevant to in vivo physiology. To this end, several laboratories have reported that endogenous ouabain and marinobufagenin are circulated at sub-nM to nM concentrations in normal individuals and that volume expansion can significantly increase their concentrations (Hamlyn et al, 1991;Fedorova et al, 2002;Bauer et al, 2005). Thus, it is conceivable that the described regulation may be relevant to in vivo physiopathology if future in vivo studies confirm our in vitro experiments.…”

Selective association of endogenous ouabain with subclinical organ damage in treated hypertensive patients

“…3,4 Their results suggested that these activations can be inhibited with b-blocker, angiotensin converting enzyme inhibitor and digoxin immune fab (antigen-binding fragments), Digi-Bind. 5,6 The increased level of EO may have direct and indirect (via marinobufagenin) vasoconstrictor (hypertensive) effects by blocking sodium/potassium pump (Na þ /K þ -ATPase), consecutively increasing intracellular calcium level by the activation of the sodium-calcium exchanger, but this effect of EO is not homogenous, that is different Na þ /K þ -ATPase isoforms respond differently to EO. [7][8][9] Experimental use of low doses of ouabain increased arterial blood pressure in rats.…”

The cardiac glycoside binding site on the Na,K-ATPase α2 isoform plays a role in the dynamic regulation of active transport in skeletal muscle

“…This site is the only known receptor for ouabain and other clinically useful cardiac glycosides and cardiac glycoside antagonists (1,2). It is also the receptor for endogenous cardiotonic steroids (3) that are present in mammals and whose circulating levels change under meaningful physiological and pathophysiological conditions, including physical exercise, essential hypertension, renal failure and hypertensive pregnancy (4)(5)(6)(7)(8).…”