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1. Rats were anaesthetized with chloralose and prepared for electrical stimulation of the cervical sympathetic trunk. The effect of such stimulation was studied on the incorporation of intravenously infused [(3)H]noradrenaline, [(3)H]adrenaline or [(3)H]dopamine by the submaxillary gland.2. A train of 200 stimuli every min for 30 min at 20/sec increased the total incorporation of [(3)H]noradrenaline by 92% over the unstimulated side of the gland, at 50/sec by about 200% and at 3.3/sec by about 30%. The incorporation of [(3)H]adrenaline and of [(3)H]dopamine was also increased by sympathetic stimulation.3. The increases in unaltered [(3)H]noradrenaline and its metabolites were proportional to the increase in total radioactivity.4. Mean venous outflow from the gland was decreased by 15-30% by the sympathetic stimulation.5. After elimination of extraneuronal binding of noradrenaline by ligation of the common excretory ducts, nerve stimulation still increased incorporation.6. Inhibition of normetanephrine production by pyrogallol did not antagonize the nerve impulse-mediated increase of [(3)H]noradrenaline incorporation. alpha-Methyltyrosine was also without effect.7. Desmethylimipramine and bretylium completely abolished the nerve impulse-mediated increase of [(3)H]noradrenaline incorporation in concentrations which did not affect the control uptake or abolish adrenergic transmission.8. Reserpine, guanethidine and phenoxybenzamine antagonized both the control and nerve impulse-mediated incorporations of [(3)H]noradrenaline.9. The results indicate that nerve impulses modulate the incorporation of transmitter amine at the neuronal membrane. Possible mechanisms for this modulation are discussed.

1. The concentration of Ca in the arterial blood plasma perfusing submandibular glands of anaesthetized cats and possums (Trichosurus vulpecula) was altered by constant-rate close arterial injection of isotonic CaCl(2) or EDTA solutions.2. There were no significant changes in the resting potentials of surface acinar cells in either species when the arterial plasma Ca concentration was altered over the range 0-30 mM.3. Secretory potentials in response to parasympathetic stimuli and close arterial injection of ACh were reduced and finally abolished during EDTA injection, but temporarily restored by injection of CaCl(2).4. Secretory potentials in response to 1 Hz parasympathetic stimuli in the cat were enhanced by increasing the gland arterial Ca concentration up to 5 mM; but responses to 10 Hz stimuli or close arterial ACh injection were not affected. There was no such enhancement of secretory potentials in the possum.5. Increase in the gland arterial plasma Ca concentration above 5 mM caused reduction in the amplitudes of the secretory potentials to all stimuli in both species, until they were abolished at 7-10 mM in the possum and 15-20 mM in the cat.6. In both species, increase in the gland arterial plasma Ca concentration caused increase in the gland blood flow and enhancement of the vasodilator effects of parasympathetic stimuli and ACh injection. EDTA injection was sometimes associated with a vasoconstrictor response to parasympathetic stimuli.7. It is concluded that the secretory potentials, but not the resting potentials, of submandibular secretory cells require the presence of Ca in the interstitial fluid. It is suggested that Ca affects both the release of transmitter and at higher concentration the mechanism by which it activates the secretory cells.