Arginine metabolism in the salivary glands of protein-deficient rats and its potential association with the oral microflora.

Salivary glands and their secretions play key roles in the prevention of dental diseases. The antibacterial and physicochemical properties of saliva are compromised in chronic malnutrition. The present study has examined the possibility that some malnutrition-induced changes in salivary gland function are potentially capable of promoting growth and metabolic activities of pathogenic oral microorganisms. Compared to well-fed controls, rats fed a 3% protein diet for 18 days showed a significant reduction (p < 0.001) in the submandibular gland arginase (L-arginine amidinohydrolase, EC 3.5.3.1) activity. Associated with the latter finding was a marked increase (+85%) in the glandular level of free arginine, this basic amino acid accounting for 12.2% of the total essential amino acids as compared with a figure of only 4.6% for the controls. The total free amino acid pool in whole saliva was relatively unaffected by malnutrition, but the levels of the basic amino acids arginine and histidine were marginally increased. Many oral bacterial species, some of which are dominant plaque microorganisms, utilize the arginine deiminase (EC 3.5.3.6) pathway. Thus, increased availability of free arginine from salivary glands offers a plausible explanation for the frequently reported observation of differential overgrowth of several potentially pathogenic microorganisms including some mutants streptococci in protein-deficient laboratory animals and may well apply to similar findings in malnourished populations in Third World countries.