Hemolysis colloids

Saponins consist of a terpenoid core (the aglycone), having oxygenated positions bound to sugar moieties (up to ten monosaccharidic units). In water they form colloidal solutions which foam on shaking and precipitate cholesterol. When saponins are near cell membranes, their interaction with cholesterol may create pore-like structures that eventually cause the membrane to burst. Hemolysis is an example of this phenomenon (i.e. the distraction of erythocyte membranes, but not hemoglobin). Occasionally, they cause hypersecretion, which could explain their expectorant activities and also their toxicity to fish. 

However, in the horse, the administration of a highly concentrated formula of hypertonic saline-dextran 70 resulted in clinically apparent intravascular hemolysis and hemoglobinuria (Moon et al 1991). Whether less-concentrated formulas are suitable for the horse remains to be investigated. The combination of an alternative colloid, hetastarch (lOml/kg), and hypertonic saline (4 ml/kg) may be an appropriate solution for the resuscitation of horses that are both hypovolemic and dehydrated. Clinical experience suggests that hypertonic-saline-hetastarch is particularly useful in horses with marked hypovolemia and hypoproteinemia, such as those with severe colitis, but this has not been formally evaluated in experimental studies or clinical cases. 

The Donnan distribution does not result in osmotic equilibrium. The sum of diffusible ions is higher inside than outside and, consequently, the pressure inside must be higher. This is aggravated by the colloid-osmotic pressure of the macromolecules. The cell walls have to adjust to the rise of pressure if this is not possible, the cells burst. This is the case, for example, with erythrocytes if they become permeable to cations and become subject to the Donnan laws (osmotic hemolysis). 

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