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J Pharm Sci. 1995 Jan;84(1):62-4.

Nasal mucosal metabolism and absorption of pentapeptide enkephalin analogs having varying N-terminal amino acids.

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DuPont Merck Pharmaceutical Company, Wilmington, DE 19880-0400.


A series of enkephalin analogs with varying amino acids on the N-terminus were synthesized and evaluated in rats in situ for their hydrolytic stability and absorption when administered nasally. The amino acids on the N-terminus were tyrosine (Y), alanine (A), serine (S), lysine (K), and aspartic acid (D). These amino acids represent different charges and sizes. Among these peptides, only the peptide carrying aspartic acid on the N-terminus was stable. The rank order of degradation rates was YGGFL > AGGFL > SGGFL, KGGFL > DGGFL. These results suggest that there are relatively high activities of aminopeptidases N and B and relatively low activity of aminopeptidase A in the rat nasal mucosa. Absorption studies were performed to determine the absorption rate of DGGFL, by measuring percentage recovery of nasal doses vs time. After a 50 microL dose of a 3 mg/mL solution, this peptide exhibited an absorption half-life of 21 min, which is similar to the nasal absorption rate of YGGFL.

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