[Structural features of linear and cyclic analogs of angiotensin, affecting secretion of histamine from rat mast...

Linear and cyclic analogues of angiotensin were studied to clarify the structural properties of peptides possessing a histamine-releasing action. It was shown that an increase in the angiotensin basicity or its cyclization leads to the appearance of the histamine-releasing activity which is not characteristic of the natural hormone. This increase in the basicity of the angiotensin cyclic analogs results in highly active compounds with the EC50 exceeding by 2 to 3 orders of magnitude that of polymyxin B or substance 48/80. The data obtained confirm the hypothesis postulating a high degree of amphiphilicity for histamine-releasing peptides. As a result of cyclization of angiotensin analogues, a block of positively charged amino acids with an oppositely located hydrophobic region is formed. This finding can be of importance for the effective interaction of peptides with cellular structures as well as for the stimulation of secretory processes.