Rectal absorption of E-2078 (dynorphin analogue peptide) in rats

The plasma levels in rats of a dynorphin analogue peptide (E-2078) after rectal administration have been studied. The bioavailabilities of E-2078 after rectal administration, subcutaneous injection, intramuscular injection, and oral administration were 21.6, 67.8, 67.1, 0.7%, respectively. The effect of dose, pH, osmolarity and viscosity on the rectal absorption of E-2078 were studied. A sigmoid relationship between the dose and the AUC was observed on rectal administration, while there was a linear relationship on intramuscular administration. The AUC was increased in acidic solution and highly viscous solution. The osmolarity did not affect the absorption of E-2078. In microscopic studies, E-2078 caused little or no damage to the rectal mucosa in rats.