Proabsorptive effect of glycerol as a glucose substitute in oral rehydration solutions

We hypothesized that glycerol, a readily diffusable hydrophilic substance, may effectively substitute for glucose and enhance intestinal water and sodium absorption in an oral rehydration solution (ORS). This was evaluated using a low osmolality (230-240 mOsm/kg) ORS containing 75 mmol/L sodium and a combination of glucose:glycerol (in mmol/L) 75:0, 50:25; 37.5:37.5, 25:50, 10:65, or 0:75 during 3-hour long in vivo rat jejunal perfusions. Water, sodium, potassium, glucose and glycerol absorption, and unidirectional fluid movement (J(in), J(eff)) were determined. Sodium and net water absorptions were maximal at glucose:glycerol ratios between 37.5:37.5 and 10:65 mmol/L. In the absence of glucose (0:75), absorption of water and electrolytes was lower than at any other concentration. The greater net rehydration seemed to be due to a higher J(in) as glycerol was increased up to 65 mmol/L. Potassium absorption followed a similar pattern. With 50 mmol/L glycerol and 25 mmol/L glucose, there was a marked expansion of the lamina propria extracellular space and increased intercellular expansion between enterocytes. These results indicate that glycerol may be an effective partial substitute for glucose in ready-to-use ORS by producing an improved rate of water and electrolyte absorption.