Abstract
Summary
Calcium concentration of saliva, when electrical stimulation of the parasympathetic postganglionic fibers to rat parotid is used to evoke secretion, increases with increases in flow rate, but both calcium concentration and flow rate reach maximal levels at frequencies of 16 Hz. The concentration of calcium at highest flow rate is three times that of serum. Amylase activity of the saliva remains consistently low at all flow rates. Therefore, these data show that while calcium and amylase are secreted together, some calcium may be secreted without amylase. By inference it is also possible to suggest that the concentrating mechanism for calcium is at the acinar level, and that as the precursor fluid, rich in calcium, flows through the duct system, very little absorption of calcium by ductal cells occurs at high flow rates, but as contact time is increased with decreasing flow rate, more calcium is reabsorbed, resulting in a final saliva low in calcium. It is not likely that the increased calcium concentration is the result of reabsorption of water by ductal cells since in perfused main submaxillary duct at least, the duct cells are relatively impermeable to water. The present data suggest this interpretation, but micropuncture analysis of calcium concentration of the precursor fluid is required to establish this as a fact. Flow rate differences found with different kinds of autonomic stimulation cannot be used to assess relationships between calcium concentration and flow rate of saliva, and only when the flow rate and calcium concentration are compared with a particular kind of autonomic stimulation are such comparisons meaningful.
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