No reduction of blood glucose in diabetic rats after oral administration of insulin liposomes prepared under acidic conditions.

Insulin liposomes (dipalmitoyl phosphatidylcholine or dimyristoyl phosphatidylcholine/cholesterol = 7/2) were prepared under strongly acidic conditions maintaining the biological activity of insulin. Although these were apparently noncharged liposomes, the association of insulin with membrane of liposomes was unexpectedly very large, and the uptake % of insulin was high. The distribution of vesicle-size of liposomes was narrow; the average diameter was 9.1 micrometer and no multilayered structures were observed by electron microscopy. Oral administration of the insulin liposomes (15-30 IU/rat) in streptozotocin-diabetic rats did not result in any distinct tendency to reduce the level of blood glucose.