[What control solutions should be used in studies on the acute effect of alcohol on the gastrointestinal tract?]

There exists still a considerable confusion in the literature about the appropriate control solution for ethanol. In many studies either no control or equimolar solutions of urea, mannitol or sodium chloride were used as an osmotic control for ethanol; distilled water being given only in a few cases. The confusion is mainly derived from the opinion that the osmolality of the ethanol solution as measured by freezing point depression (= "theoretical osmotic pressure") is the determinant factor for the action of ethanol on the gastrointestinal tract. This opinion, however, is not correct. Since biological membranes are not perfectly semipermeable (i. e., they are permeable to certain solutes) the "effective osmotic pressure" produced by permeant solutes is always less than the ("theoretical") osmotic pressure as determined by freezing point depression. The ratio of the "effective" to the "theoretical" osmotic pressure of a solute is defined by the Stavermann reflection coefficient for a certain membrane. The Stavermann reflection coefficient may have any value between 1 and 0. For an impermeant solute the reflection coefficient equals 1 and for increasingly permeant solutes it becomes progressively less than 1 and closer to 0. The Stavermann reflection coefficient of ethanol for some gastrointestinal organs tested is about 0.1. The ideal osmotic control for ethanol would be a solute which exerts the same effective osmotic pressure on the gastrointestinal membrane as ethanol, i. e. which has the same Stavermann reflection coefficient as ethanol, and has no specific pharmacologic effect. Distilled water seems to be the most suitable osmotic control for ethanol because it has a Stavermann reflection coefficient of 0 and has no pharmacological actions.(ABSTRACT TRUNCATED AT 250 WORDS)