Noradrenaline and dopamine-beta-hydroxylase levels in rat salivary glands after preganglionic nerve stimulation: evidence for re-use of amine storage granules in transmitter release.

Abstract

The levels of endogenous noradrenaline (NA) in rat salivary glands were reduced to about 40 per cent after 1 hour of preganglionic stimulation at 4 Hz. Following 2 to 3 hours of rest the NA values had recovered to normal and remained normal for 6 hours after the stimulation. The recovered NA could be depleted by renewed nerve stimulation. After treatment with reserpine the NA disappeared almost completely. The recovered NA is discussed to be mainly present in amine storage granules that are re-used for storage and transmitter release. The axonal down-transport of new granules to the nerve terminals appears to be too small, as based on earlier results, for being of any quantitative importance in the experimental situation. The dopamine-beta-hydroxylase (DBH) level in the glands did not significantly change after the period of stimulation. The DBH content remained mainly unchanged following either post-stimulation recovery, repeated stimulation, or reserpine treatment. First when the glands were stimulated for 4 hours, there was a small decrease of the DBH levels. The mainly unchanged levels of DBH after stimulation does not appear to be explained by "trapping" in the tissue of released DBH, or recovery of the DBH by a marked axonal down-transport of new granules, as based on earlier results. The results of the DBH estimations support the view that the granules are not consumed to any marked extent at nerve activity, but can be re-used for nerve transmission. Furthermore, the results are in agreement with lack of correlation between released NA and released DBH.