Ionic, histological and vascular factors in the reaction of the sheep's parotid to high and low mineralocorticoid status.

1. The blood capillaries from the alveolar areas of the sheep's parotid gland drain into a sinusoidal portal venous system which is in close relation to the striated intralobular ducts.2. The alveoli of the gland are surrounded by a mesh of muscular processes of myoepithelial cells: there are no myoepithelial structures in relation to the ducts.3. In close relation to the alveoli are nerve fibres, some containing noradrenaline and some with cholinesterase at their cellular contact area. Stimulation of the cervical sympathetic trunk for 1-2 min (or intra-arterial injection of noradrenaline) causes expulsion from each gland of a regular amount of saliva without changing the long term appearance rate of saliva. Stimulation of the secretomotor nerve (or acetylcholine I.A.) causes an increase in saliva production.4. It is proposed that the saliva which appears due to sympathetic stimulation is expelled from the alveoli by contraction of the myoepithelial network and is little changed during its rapid transit through the duct system.5. The results indicate that the alveolar cells react to increasing aldosterone status by increasing concentration of K(+) in alveolar fluid with inverse change of Na(+) in alveolar secretion over a wide range of flow rates.6. No histological evidence of innervation of the intralobular striated ducts by sympathetic or secretomotor nerves was obtained.7. The secretory ducts appear to be the site of exchange of HCO(3) (-) and phosphate, Na(+) and K(+), and for enrichment of SCN(-) and I(-) in the alveolar fluid.8. During stimulation of the secretomotor nerve supply, the gland, whether in adrenally insufficient or in hyperaldosterone status, shows the initial transient of discharge of K(+) into saliva and blood and then maintains K(+) intake from plasma as near to output in saliva as does the gland in the replete animal with basal aldosterone status.