Leon H. Schneyer

REGULATION OF SALIVARY GLAND AMYLASE ACTIVITY

Secretory activity by digestive glands is characteristically periodic. This periodicity is distinguishable even in such glands as rat pancreas and human submaxillary and parotid, which exhibit a tendency toward continuous basal secretion. During periods of activity several of the digestive glands discharge relatively large quantities of hydrolytic enzymes into carrier secretory fluid and, perhaps, into the blood. In such cases a relationship between secretory discharge and ensuing reconstitution of secretory protein stores in the gland has frequently been assumed; the clearest exposition of this has been that of Langstroth et a1.I Langstroth and his co-workers selected the pancreas as their biological experimental system. Here, initial secretion in response to an appropriate stimulating agent involves depletion of preformed gland stores of secretable protein, for example, hydrolytic enzymes and enzyme precursors. Cessation of stimulation leads eventually to replenishment of gland protein stores as a result of synthesis of new protein by the pancreas cells. This replenishment process is unaffected by blockage of parasympathetic influences. Langstroth and his co-workers postulated that intermediate reactions in the synthesis process are reversible. Adherence to the law of mass action would then link synthesis rate to degree of depletion. The assumptions are simple and, in the light of newer work on amino acid activation and incorporation, they are also plausible. Additional information concerning actual synthesis rates a t various stages of the secretion cycle is, however, urgently needed. In contrast to the sequence of events described for the pancreas and characteristic also of the parotid gland-that is, stimulation, depletion and then synthesis-the pattern of active enzyme accumulation in the submaxillarysublingual gland of the rat is wholly different. Stimulation of this gland, instead of depleting the tissue of amylase, a secretory enzyme, leads to a rapid, progressive, and appreciable rise in gland amylase level. This rise is dependent on continuing parasympathomimetic influence. Evidence indicates that amylase accumulation in the submaxillary-sublingual gland of the rat is the result, as in the pancreas, of synthesis of new enzyme. In the case of the submaxillarysublingual gland, however, this synthesis is subject to relatively direct regulation by the parasympathetic branch of the autonomic nervous system.

Neural Regulation of Calcium and Amylase of Rat Parotid Saliva

Summary The course of amylase and calcium secretion into saliva is described under diverse conditions of autonomic stimulation of parotid. Of special importance is the fact that for the first time calcium levels of saliva were measured under conditions of nerve stimulation. Initial levels of calcium with stimulation of the parasympathetic innervation were as high as those evoked by stimulation of the sympathetic innervation. While calcium and amylase levels were characteristically high with adrenergic stimulation (either following drug administration or nerve stimulation), amylase levels following stimulation of the parasympathetic nerve were characteristically low. In fact, a parallelism between secretion of calcium and amylase was not observed under conditions of cholinergic nerve stimulation, but was observed with adrenergic nerve stimulation. It is suggested that with cholinergic nerve stimulation mediation of calcium and amylase secretion may differ from that observed with adrenergic stimulation.

Total Salivary Calcium and Amylase Output of Rat Parotid with Electrical Stimulation of Autonomic Innervation

Summary Calcium levels of rat parotid saliva evoked by stimulation of the auriculotemporal nerve are high (11 mEq/1) and in fact, higher than those evoked by stimulation of the sympathetic innervation. Total calcium output in the cholinergically-evoked saliva is also very high but the depletion of gland levels is insignificant 20 or even 60 min after the initiation of stimulation. With sympathetic stimulation, there is a closer correlation between gland depletion and total output of calcium in the saliva. These findings suggest that the uptake mechanism for calcium with cholinergic stimulation is more rapid than that found with adrenergic stimulation. The high levels of calcium in the cholinergically evoked saliva are also not due to acetylcho-line-induced release of catecholamines since calcium levels of cholinergically-evoked saliva are the same whether or not adrenergic blocking agents are present. The total output of amylase in the saliva when sympathetic stimulation is employed is about five times greater than that found with cholinergic stimulation, and the reduction in gland amylase under these two conditions of stimulation reflect these same relations. The data also show that there is a parallelism between depletion of gland amylase and calcium and concentration and total output of these two moieties in the saliva when adrenergic stimulation is used but that no parallelism between secretion of these substances is seen with cholinergic stimulation. It is suggested that with adrenergic stimulation all of the amylase is packaged together with calcium and the two are secreted together; however, with cholinergic stimulation, only a fraction of the total calcium is packaged with the amylase, and the remainder is transferred from blood through the gland to the saliva. Thus, two separate routes for secretion of calcium exist with cholinergic stimulation, and the pathways with the two kinds of nerve stimulation are different.

Coagulation of Salivary Mucoid by Freezing and Thawing of Saliva.

Summary 1. Freezing of chemically untreated mucoid-containing salivary secretions results in the formation of a persisting clot when the secretion is thawed. This clot resembles in appearance the mucin clot formed in response to the addition of acid. 2. Evidence from viscosity measurements, response to addition of weak acid, and “sialic acid” analyses indicates that the coagulum formed after freezing and thawing is derived from the salivary mucoid. 3. It is suggested that this effect be taken into account if storage of saliva samples in a frozen state is considered.

ELECTROLYTE SECRETION BY RAT SALIVARY GLANDS IN VIVO AND IN VITRO.

ABSTRACT Salivary secretion has been investigated, in the rat, in vivo and in incubated gland slices, with the ultimate objective of delineating mechanisms of transport of fluid and electrolytes. As an initial phase of the work, electrolyte composition was investigated in the major salivary secretions and in the salivary glands themselves. In glands, composition was determined for the whole organ and, by means of “space” studies, for the salivary gland cells. Following this phase, transport mechanisms were investigated in vitro , using slices of submaxillary gland. With slices, cells could be loaded with sodium and depleted of potassium during aerobic or, to appreciably greater extent, during anaerobic incubation. Reaccumulation of cell potassium and extrusion of sodium were consistently observed when oxygen was readmitted after anaerobic incubation. It was noted that these exchanges occurred against chemical and electrical potential gradients. Chloride was accumulated by cells during anaerobic incubation but was not extruded when oxygen was readmitted. Active transport of sodium and potassium, but not of chloride, were, thus, established for rat submaxillary gland cells. Preliminary data suggested that stimulation by pilocarpine reduced the net efflux of sodium and the net influx of potassium during aerobic incubation following anaerobiosis, that is, in a situation where these net fluxes involve active transport of sodium and potassium. Preliminary investigation of one-way movements of ions during this period suggested that pilocarpine increased sodium influx and did not affect sodium efflux or potassium influx. These and other observations are examined in relation to current hypotheses on the mode of formation of a secretory fluid.

Inhibition of salivary amylase by uranium

Abstract Uranium nitrate, an inhibitor which appears to affect selected enzyme systems by a reversible combination at electronegative groups, inhibits salivary amylase activity completely in a concentration of 10 −3 M . The inhibition is not affected by doubling enzyme concentration but is reduced by increasing substrate concentration or by the introduction of organic α-OH dicarboxylic acids.