Inflammation and Related Phenomena 113 



for a hundred years, but the study of the effect of peptides on 

 capillaries really dates from some observations of Menkin (1956). 

 Menkin showed that albumin partially digested with trypsin in- 

 creased capillary permeability and that the property was likely to 

 reside in the peptide fraction. Later work demonstrated that large 

 numbers of different peptides from various sources were able to 

 increase capillary permeability and that the most likely requisite 

 for this property was a molecule containing eight to twelve amino 

 acids. In addition, pharmacologists began to describe a variety of 

 individual peptides which they found in urine, blood and tissue 

 extracts and that increased capillary permeability (see Spector, 

 1958). These observations culminated recently in the purification 

 of one of the most important members of the group, bradykin, a 

 peptide derived by proteolysis from plasma globulin. In conformity 

 with the earlier analyses, this substance was found to contain eight 

 amino acids in its molecule. All peptides that affect capillary per- 

 meability have certain common properties. They stimulate plain 

 muscle, e.g. of uterus and intestine, behave as chemical bases on 

 electrophoresis, tend to be hypotensive in dogs and cats, to cause 

 pain on application to a blister base and to be inactivated by 

 chymotrypsin. Those derived from blood plasma usually originate 

 in the or globulin fraction. It is now customary to refer to peptides 

 of this type as kinins. 



It is thus obvious that peptides are capable of the role of 

 chemical mediator of altered capillary permeability after injury. 

 Unfortunately, it has proved difficult to demonstrate their pres- 

 ence at the time and place needed to establish their causative role. 

 One possible exception is provided by stimulation of the nerve 

 supplying salivary gland tissue. Such stimulation leads to inflam- 

 matory-like changes in the vessels of the gland and also to the 

 appearance of kinins in the effluent from the gland (Hilton and 

 Lewis, 1955) . It is very possible that much of the difficulty hither- 

 to experienced is due to rapid destruction of the peptides by 

 peptidases in blood and tissues. It is known that kinins activated 

 in plasma, e.g. by contact with glass, are destroyed in a few minutes 

 by such enzymes, and it seems likely that peptides activated by 

 tissue injury would enjoy an equally transient existence. More- 



