Increase in plasma immunoreactive insulin following administration of insulin to the gastrointestinal tract of rabbits

Improvement of Large Intestinal Absorption of Insulin by Chemical Modification with Palmitic Acid in Rats

The intestinal absorption of 125I-labelled palmitoyl insulin was examined following administration into in-situ closed large intestinal loops of rats. When mono- and dipalmitoyl insulins (Palins-1 and Palins-2, respectively) were administered in polyoxyethylene hydrogenated castor oil (HCO 60) micellar system into intestinal loops, a marked increase in plasma radioactivity and a corresponding disappearance of residual radioactivity in the intestinal lumen were observed in the following rank order: Palins-2 > Palins-1 > native insulin. In addition, the derivatives were more stable than native insulin in the mucosal tissue homogenates of the large intestine. These results suggest that chemical modification of insulin with palmitic acid may not only increase the lipophilicity of insulin but also reduce its degradation, resulting in the increased transfer of insulin across the large intestinal mucous membrane. The linoleic acid-HCO 60 mixed micelles system did not have a significant effect on the large intestinal absorption of radioactivity associated with the lipophilic insulin analogues.

Absorption and disposition of epithiosteroids in rats (1): Route of administration and plasma levels of epitiostanol

1. Absorption and disposition of epitiostanol (EP) were determined following intramuscular (i.m.), intravenous (i.v.) and oral administration of 14C-epitiostanol (14C-EP) to rats. 2. When 14C-EP was administered orally, radioactivity was absorbed from the gastrointestinal tract and appeared in the systemic circulation, but no unchanged EP was detected in the plasma. EP was extensively metabolized by first-pass metabolism in the intestinal mucosa and liver, and because of the low biological activity when given orally, EP should be given by injection. 3. The EP plasma concentration/time curve following i.m. administration is analysed by a flip-flop model (ka less than kel), because the ka for EP remaining at the i.m. injection site was less than the kel for i.v. injection.

Pharmaceutical approach to subcutaneous dosage forms of insulin

The present studies were undertaken to describe the dynamic nature of the degradation and absorption of insulin in the subcutaneous injection site and to develop agents which would stabilize this dosage form. [125I]Insulin with 0.2-U/kg of unlabeled insulin in 10 microliters of aqueous solution was injected subcutaneously in rats under the depilated skin of the back. At various times, radioactive skin tissue was extracted and assayed for insulin and/or its metabolites by gel filtration. Using these data, absorption and degradation rate constants of these substances were estimated according to a one-compartment model. Absorption rate constants of insulin and its metabolite of low molecular weight (monoiodotyrosine) were 0.021 min-1 and 0.107 min-1, respectively, while the degradation rate constant for insulin to monoiodotyrosine was 0.013 min-1. Thus, the bioavailability of insulin injected subcutaneously was lower than expected, suggesting the necessity of stabilizing methods. The protection of insulin from degradation at the site of injection was examined by the addition of various peptides. It was found that benzyloxycarbonyl-Gly-Pro-Leu-Gly was a good stabilizing agent, and remarkably inhibited insulin degradation. This inhibition was confirmed by the increase of immunoreactive insulin level and the decrease of the blood glucose level. We postulated that this peptide protects the injected insulin from degradation by inhibiting the peptidase present in subcutaneous tissue.