Biochemical composition and electrolyte balance of "unstimulated" whole human saliva

The biochemical composition of "unstimulated" whole saliva was determined i n healthy adult subjects. Based on their relative concentration, salivary a nalytes could be classified into three arbitrary categories: concentration lower than in serum (saliva/serum ratio < 0.5; 12 analytes), similar to ser um (ratio = 0.5-1.5; five analytes), and higher than in serum (ratio > 1.5; five analytes). Consistent with local production, an elevated lactate dehy drogenase (LDH) activity in the saliva was associated with a non-serum like LDH isoenzyme pattern: LDH5 much greater than LDH4 > LDH3 much greater tha n LDH2 > LDH1. Compared with serum, the concentrations of hydrogen (as refl ected in the pH), potassium and inorganic phosphorus were much higher (sali va/serum ratio greater than or equal to 3), whereas that of sodium, total m agnesium, chloride, and total carbon dioxide were lower (saliva/serum ratio less than or equal to 0.3). The concentration of ionized calcium was simil ar in saliva and serum (saliva/serum ratio = 0.8), while ionized magnesium was unmeasurable in saliva. The salivary ionized calcium fraction was highe r (0.76) than previously suggested (0.51). The difference between the main salivary cations (potassium, sodium), and anions (phosphate, chloride) was similar to serum (anion gap: 4 vs. 11 meq/l). Highly significant (p less th an or equal to 0.012) correlations occured among salivary pH, dihydrophosph ate, total calcium, and potassium. Our data suggest that calcium, potassium , chloride and phosphates are the major salivary complex-forming ions. The major compositional differences between serum and saliva show that saliva i s not a passive "ultrafiltrate" of serum and salivary constituents may play a distinct physiological role.