[4] Ouabain can be found in the roots, stems, leaves, and seeds of the Acokanthera schimperi and Strophanthus gratus plants, both of which are native to eastern Africa.

The change in ionic gradients caused by ouabain can also affect the membrane voltage of the cell and result in cardiac arrhythmias.

An overdose of ouabain can be detected by the presence of the following symptoms: rapid twitching of the neck and chest musculature, respiratory distress, increased and irregular heartbeat, rise in blood pressure, convulsions, wheezing, clicking, and gasping rattling.

[5] Ouabain is a highly toxic compound, however, it has a low bioavailability[2] and is absorbed poorly from the alimentary tract as so much of the oral dose is destroyed.

A number of analytical techniques led to the conclusion that this circulating molecule was ouabain and that humans were producing it as an endogenous hormone.

[8] A large portion of the scientific community agreed that this inhibitor was endogenous ouabain and that there was strong evidence to indicate that it was synthesized in the adrenal gland.

Critically, the primary observations concerning the identification of ouabain in mammals were repeated and confirmed using a variety of tissue sources on three different continents with advanced analytical methods as summarized elsewhere.

[14][15] The African crested rat (Lophiomys imhausi) has a broad, white-bordered strip of hairs covering an area of glandular skin on the flank.

When the animal is threatened or excited, the mane on its back erects and this flank strip parts, exposing the glandular area.

[19] It was synthesized under the hypothesis that a polyanionic cyclization (double Michael addition followed by aldol condensation) would allow access to a tetracyclic intermediate with the desired functionality.

Poisons derived from Acokanthera plants are known to have been used in Africa as far back as the 3rd century BC when Theophrastus reported a toxic substance that the Ethiopians would smear on their arrows.

Acokanthera schimperi, in particular, exhibits a very large amount of ouabain, which the Kenyans, Tanzanians, Rwandans, Ethiopians, and Somalis would use as an arrow poison.

[5] Often, certain magical additives were also mixed in with the ouabain extract in order to make the poison work according to the hunter's wishes.

[5] They had observed that an elephant shrew would always run straight ahead or follow a direct path and thought that these properties would be transferred to the poison.