180 Organic Constituents of Saliva 



(Hoerman, Englander and Shklair, 1956) and can be separated 

 electrophoretically because it behaves as a cation at the usual pH 

 employed for electrophoresis (Kinersley and Hogberg, 1955). The 

 contribution of lysozyme to the antibacterial properties of saliva 

 is still under debate (Thompson, 1940; Salton, 1957). 



KALLIKREIN AND FACTORS CONCERNED IN BLOOD 

 COAGULATION 



Injection of saliva intravenously produces a short-lived fall of 

 blood pressure (Seeker, 1934; Feldberg and Guimarais, 1935). 

 This effect was analysed in detail by Werle (Frey, Kraut and 

 Werle, 1950; Werle, 1955) who showed that an enzyme in saliva 

 and other body fluids and tissues acted on a plasma protein setting 

 free a vasodilator polypeptide. The enzyme is called kallikrein and 

 the polypeptide kallidin. Kallidin appears to be identical with 

 bradykinin and the common name of plasma kinin has been 

 adopted for this peptide. Kallikrein is found in both submaxillary 

 and parotid secretion in man, cat, dog and cow, but not in the 

 horse. The enzyme has also been detected in the perfusate from 

 Ringer perfused salivary glands (Werle and Roden, 1939). Hilton 

 and Lewis (1957) have proposed that kallikrein release is respon- 

 sible for the functional vasodilatation in the salivary gland during 

 activity (see page 131) and have also shown the presence of a 

 kinin-destroying enzyme in saliva. Presumably both kinin produc- 

 tion and destruction are due to the presence of proteolytic enzymes 

 in saliva, but these must be quite specific in their action since 

 they are unable to hydrolyse serum albumin, casein, or benzoyl 

 arginamide. The mechanism of vasodilatation in horse salivary 

 glands should be studied in view of the apparent lack of kallikrein 

 in these glands. 



Albrechtsen and Thaysen (1955) have examined human saliva 

 for components of the fibrinolytic system and have found large 

 amounts of proactivator, traces of activator, but no plasminogen. 

 Resting saliva contained more proactivator than did stimulated 

 saliva. Nour-Eldin and Wilkinson (1957) examined saliva for 

 blood-clotting factors and found activity comparable to that clas- 

 sified in plasma as Christmas factor, antihaemophilic globulin and 

 platelet factor, but no trace of factors V or VII. Saliva can replace 

 platelets in the thrombin generation test but not in thromboplastin 

 generation. Glazko and Greenberg (1939) had found a thrombo- 



