Studies of oral rehydration solutions in animal models.

Ideas about the optimal composition of oral rehydration solutions (ORS) continue to evolve. A controlled clinical trial is the only way to determine whether a new ORS is superior to an established solution, but attempts have been made to prescreen new ORS in a variety of animal models, most of which involve intestinal perfusion. Most of the work has been performed in the healthy small intestine of rats, either in short segments or in its entirety, or in the diseased small intestine that has been infected with rotavirus or exposed to cholera toxin to induce a secretory state. Despite the marked pathophysiologic differences between these models, the qualitative findings using new and established ORS have been remarkably similar. Overall, these animal models have emphasized the potential benefit of using a hypotonic ORS (osmolality, 240 mosm/kg or less). The optimal sodium concentration has been found to be 50 to 60 mmol/L, and the optimal glucose concentration 90 to 111 mmol/L. These models have also been satisfactorily used to examine the value of glucose polymer and food-based ORS. The findings suggest that for a given substrate load initial osmolality is probably the chief determinant of water absorption, which is substantially greater from the more hypotonic solutions. Results from animal experiments must be interpreted with caution because of their physiologic limitations. Nevertheless, they have provided insight into the physiology of oral rehydration therapy and may be useful in identifying ORS for evaluation by clinical trial.