STUDIES ON MECHANISM OF SALIVARY SECRETION

抄録

In order to clarify the secretory mechanism of water through the salivary gland, experiments were carried out, in association with electronmicroscopic observations, on the secretion of human parotid glands and the dog's submaxillary glands with pilocarpine or electrical stimulation of the chorda tympani. Results obtained are as follows:
1. Electron microscopic observations were made with the dog's submaxillary gland before and after pilocarpine injection. After pilocarpine, the myoepithelium, presented a shape indicating its contraction wide clear spaces of dilated intercellular canaliculi were recognized between the myoepithelium and gland cell, as well as between the neighboring two gland cells, which are usually tightly attached at rest.
2. The secretion pressure showed a sharp rise to a height of about 150 mmHg immediately after stimulation and fluctuated rhythmically at this level in the range of about 5 mmHg. The count of salivary drops increased parallel with the increase of secretion pressure.
3. The salivogram was composed of two kinds of waves; i. e., a large negative wave which appeared immediately after the beginning of secretion, and small, rhythmical fluctuations with frequency of 17-20/min. The large negative potential, corresponding to the sharp rise of secretion pressure, is the so-called secretion potential, while the small waves of salivogram corresponding to small fiuctuations of secretion pressure, may be the myograp of the myoepithellup around the gland acinus.
4. The small waves of salivogram increase their frequency and amplitude after the oxytocin administration, probably due to acceleration of myoepithelium contration.
5. From the results of the present experiments together with those reported in the previous paper, the following hypothesis on the mechanism of salivary secretion was presented:
The anion pump is located at the basement membrane of the salivary gland, and it is activated by pilocarpine or nervous stimulation, thus initiating a large negative secretion potential. The transport of anion is necessarily accompanied with cation transport and with osmosis of water in tissue fluid, thus producing the precursor saliva underneath the basement membrane. This precursor saliva, of which the salt composition resembles much tissue fluid, may be compressed by rhythmical contractions of the myoepithelium and forced out through intercellular spaces of gland cells into the acinus lumen and hence into the duct.A part of intracellular water which contains amylase and K in high concentrations is also forced out by this compression and is mixed with the extracellular fluid passed through intercellular space.
6. By analysing the curves of amylase activity and K concentration in relation to the rate of salivary flow, the ratio of the amount of water passing through the intracellular compartment to that of the total saliva was calculated, under the postulation that saliva is composed of salt solutions originated from the intracellular and extracellular fluids in acinus, and it was found that the minimum ratio is about 19% and the maximum is 45% which corresponds to the rate of the intracellular water secreted at the minimum rate of salivary flow. Consequently, over half the amount of salivary water is produced by passing through the intercellular space.
7. The precursor saliva produced in the terminal portion of the gland is subjected to the reabsorption of some part of salts and the secretion of bicarbonate, by passing through the striated part of the duct, thus forming the final saliva which is hypotonic and slightly alkaline. The authors wish to express their sincere gratitude to Dr. M. VISSCHER, chairman of the Travelling Mission of International Union of Physiological Sciences for his valuable suggestion.