ABSTRACT
Peptides are major players in a variety of physiological processes in mammals and microorganisms. Being neurotransmitters in the nervous system, the neuropeptides constitute a large and signicant group of peptides, which often coexist with other neurotransmitters in the neurons (Hökfelt et al. 2000; Hökfelt, Bartfai, and Bloom 2003). As a result of their effect on living organisms, biologically active peptides are interesting starting points in drug discovery. Although peptides can serve as valuable research tools in the rst phase of drug discovery projects and for the initial study of biological mechanisms of various diseases, they are not suitable as pharmaceuticals intended for oral administration. This is due to the inherent drawbacks of the peptide structure, which is associated with rapid degradation by proteolytic enzymes and low bioavailability.
