showed that Met-Enk is most stable at pH approximately 5.0. Various mucosae excised from rabbit were mounted on Valia-Chien permeation cells and exposed to isotonic phosphate buffer at physiologic pHs. Mucosal and serosal extracts were collected from the donor and receptor solutions, respectively. The degradation of Met-Enk in the extracts followed first-order kinetics, but no significant difference in
为了评估蛋
氨酸
脑啡肽(Tyr-Gly-Gly-Phe-Met; Met-Enk)经粘膜递送的可行性,重要的是首先研究其理化和酶稳定性。通过高效
液相色谱法在pH 2.01-9.84和37-45℃下测定Met-Enk在
水溶液中的降解动力学。计算一级速率常数(k),log k-pH曲线表明,Met-Enk在pH约5.0时最稳定。将从兔切下的各种粘膜固定在Valia-Chien渗透细胞上,并在生理pH值下暴露于等渗
磷酸盐缓冲液中。分别从供体和受体溶液中收集粘膜和浆膜
提取物。
提取物中Met-Enk的降解遵循一级动力学,但是,无论使用何种粘膜类型,粘膜和浆膜
提取物的降解率均无显着差异。直肠粘膜
提取物中降解最迅速,其次是阴道和鼻粘膜。主要代谢物是Des-Tyr-Met-Enk和
酪氨酸(Tyr),表明
氨基肽酶的酶促
水解。但是,数据还表明,二肽基肽酶和二肽基羧肽酶可能在Met-Enk的降解中起一定作用。通过