The rat parotid has been considered a salivary gland that produces saliva isotonic to plasma and with high sodium concentrations at all flow rates. We studied the excretion of sodium, potassium and total solute in the unstimulated and pilocarpine stimulated parotid of adult rats. The effects of retrograde injection of ouabain into the duct system of the gland were also investigated. Use of microanalytical methods enabled us to study the composition of the saliva at all flow rates. The saliva was isotonic to plasma at resting flow rates. Minimal increase in flow rate was associated with a precipitous drop in osmolarity to as low as 86 mOsm/l. Further increase in flow rate up to 135 mg/min/gram wet gland tissue, was followed by gradual increase of osmolarity towards isotonicity. The changes in osmolarity were mainly caused by changes in the sodium concentration. The potassium concentration of the saliva was 3-4 times that of plasma and showed little variation with changing flow rates. Retrograde injection of ouabain into the duct system of the gland up to the acini has no effect on the flow rate but partially inhibited the ability of the gland to elaborate hypotonic saliva. These findings demonstrate that, contrary to what has so far been accepted, the rat parotid is similar to the parotid of man and dog in the excretion of water and electrolytes. In addition, this work supports the hypothesis that the parotid saliva is formed by secretion of a plasma-like fluid in the acini-intercalated duct region, which is subsequently modified by active sodium reabsorption in excess of water in another site (or sites) of the duct system of the gland.
|Original language||English (US)|
|Number of pages||9|
|Journal||Pflügers Archiv für die Gesamte Physiologie des Menschen und der Tiere|
|State||Published - Jul 1966|
ASJC Scopus subject areas
- Clinical Biochemistry
- Physiology (medical)