Rectal absorption of insulin suppositories in rabbits.

When insulin solutions (100 U kg-1) at various pH values were placed in the rectum of rabbits, a large decrease in blood glucose concentration was observed except at the pH close to the iso-electric point of insulin. The effect of surface-active agents on the rectal absorption of insulin was examined by measuring the blood glucose concentration after the administration of 2 or 5 U kg-1. Non-ionic ether type, anionic, cationic and amphoteric surfactants as well as bile acids increased the absorption. The optimal effect with suppositories was reached with the addition of 1% polyoxyethylene (9) lauryl alcohol ether. Insulin suppositories containing agents enhancing rectal absorption were compared with the insulin for intravenous, intramuscular and subcutaneous injection. The changes of blood glucose and plasma immuno-reactive insulin concentration after rectal administration of insulin were similar to those after intravenous injection.