Ouabain is the familiar name of g-strophanthin, a poisonous cardiac glycoside. Ouabain is found in the ripe seeds of African plants Strophanthus gratus and Acokanthera ouabaio. K-strophanthin is found in the ripe seeds of Strophanthus kombé.

Ouabain blocks the Na⁺/K⁺-ATPase in higher concentrations which are attainable in vitro or with intravenous dosage. This is the original use of ouabain; digoxin is a generally more popular compound used for similar indications (atrial fibrillation and congestive heart failure).

A recent concept is that at low concentrations ouabain in fact has the opposite effect, namely stimulation of the Na-K-ATPase (e.g. Gao et al 2002). This property is not exhibited by digoxin (Saunders & Scheiner-Bobis 2004).

Endogenous ouabain and ouabain mimics

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In 1991 an isomer of ouabain was identified as an endogenous hormone (Hamlyn et al. 1991 & 2003), which is synthezised in the adrenal gland and in the hypothalamus. Its exact mode of action and physiological signifance is not yet determined. In human plasma 9 - 190 picoMol ouabain was found, a concentration range which causes a stimulation of the Na+/K+-ATPase.

In the years following that, it was found in the adrenal glands of cows (Schneider et al. 1998), dogs (Boulanger et al. 1993), and the "isomer" of ouabain found in the hypothalamus was shown to be ouabain that had been misidentified due to the presence of borate from the borosilicate glassware in which it had been kept (Kawamura et al. 1999).

Uses

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Ouabain is used worldwide extensively by scientists for in-vitro-studies to block the sodium pump (Na-K-ATPase) with high concentrations of this substance. In France and Germany intravenous ouabain has a history in the treatment of heart failure, and some advocate its use in angina pectoris and myocardial infarction, although there is little research supportive of this practice.

References

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• Gao J, Wymore RS, Wang Y, Gaudette GR, Krukenkamp IB, Cohen IS, Mathias RT. Isoform-specific stimulation of cardiac Na/K pumps by nanomolar concentrations of glycosides. J Gen Physiol 2002;119:297-312. PMID 11929882.
• | url = http://ajpendo.physiology.org/cgi/reprint/264/3/E413}}
• | url = http://www.pnas.org/cgi/reprint/88/14/6259}}
• | url = http://www.pnas.org/cgi/content/full/96/12/6654}}
• | url = http://www.jbc.org/cgi/content/full/273/2/784}}

External links

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• ^* Ouabainomics by Hamlyn

Cardiac glycosides

Strophanthin | Strophanthine | Ouabaïne