Sodium and potassium content in human palatine gland secretion

Archr oral Bwl. Vol. 22. pp 529 10 532. Pcrgamon Press 1977. Printed in Great Britam

SODIUM

AND POTASSIUM CONTENT IN HUMAN PALATINE GLAND SECRETION s. KMBER

Department of Prosthetic Dentistry, Royal Dental College, Aarhus. Denmark

Summary-Secretion samples were collected from the orifices of human palatine glands on discs of filter paper after intermittent mechanical stimulation of the hard palatal surface. After the sample had been weighed on a micro-balance, its content of Na and K was determined by flame photometry. Secretory drops from previously resting glands, with a weight below 500 ccg,showed a trend to an elevated Na content when compared with restimulated secretion, whereas above that level they showed a steady state level of about 85 meq Na/kg Similar steady state concentrations of potassium with a mean value of about 15 meq/kg secretion were found in samples above SoO~g. Below that level, concentration rose steeply to values of about 90meq K/kg in drops weighing less than 250%. Sodium transients between 200-745 meq/kg independent of secretory drop size were observed after repeated stimulation. INTRODUCl-ION The palatine

glands are located in the posterior part of the hard palate, the soft palate and the uvula (Sicher and Bhaskar, 1972) Topographically they are included in the heterogeneous group of minor salivary glands @awes and Wood, 1973a) Structurally, however, they belong to a group of mucous glands with long branched tubulo-alveoli connected to single ducts found in the upper part of the digestive tract, from the posterior roof and base of the oral cavity, through the pharynx and oesophagus to the cardia (Maximow and Bloom, 1952) The palatine glands are of primary importance in the production of mucosubstances (Hensten-Pettersen, 1975). Although they and the other minor salivary glands contribute nearly 10 per cent of the total saliva volume @awes and Wood, 1973a), little is known about the composition of their secretion, due mainly to the lack of sampling methods suitable for quantitation of the sparse secretion. Schneyer (1956) made use of absorbent materials for its collection but suction procedures with use of calibrated microcapillary tubes (Kutscher et al.. 1967), of micropipettes (Dawes and Wood, 1973b) and of small syringes (Hensten-Pettersen, 1975) have been mainly employed These methods have proved useful in providing secretory material from labial glands, although the material must be pooled for analysis The procedures are, however, disadvantageous in quantitative studies. as material from glands at varying secretory stages with consequently differing solute concentrations may be included. In principle, therefore studies on the minor salivary gland secretion should be designed so that the secretion can be collected from the individual orifices. Kaaber (1971a) introduced a microgravimetric method for the determination of oral fluid using absorbent materials and small closed polyethylene containers for analysis. This method proved useful for quantitative studies on the net transport of water and electrolytes across human oral mucosa in uivo (Kaaber, 1974). As this sampling principle has been used previously for analytical studies of different types

of glandular secretion, including sweat (Dole et al.. 1951) and tears (Thaysen and Thorn, 1954). I have adopted it for similar studies on palatine gland secretion. MATERIAL AND METHODS

Collection of secretion Secretory material was obtained from 13 dental students, 6 men and 7 women, aged 19-22 years, none of whom were regular smokers Every subject exhibited a clinically healthy mucosa with a varying number of visible glandular or&es in the posterior part of the hard palate. The study was performed at 21 + 2°C in a room in which the relative humidity was registered continuously with a hygrometer. Sampling occurred in the morning, at least 90 min after previous food intake. Firstly, the mucus was removed carefully from the hard palatal surface with gauze. The exposed mucosal surface was then stimulated gently by rubbing with a chromium-plated instrument with a blunt end. When secretional activity was observed, secretory drops were collected from the single orifices into a standardized 6.3 mm-wide disc of ash-free filter paper. During sampling, material was obtained at all stages in the visible part of the secretional cycle, using the drop size as the criterion. Care was therefore taken to obtain drops as small as possible immediately after the onset of secretion. After lO-15mir1, during which the subject rested with the mouth closed, the glandular area was cleaned again and re-stimulated prior to renewed sampling. A third stimulation was also performed but in about 50 per cent of the trials the glands failed to respond. As a rule, 4-6 samples were obtained from the subject during the experiment and each sample was followed by a corresponding dummy sample being transported to and from the oral cavity without touching the mucosal surface, in order to control the electrolytic contamination during the experimental procedure. Gravimetry and photometry Prior to sampling. the filter-paper discs were cleaned by washing in distilled water and drying 529

S. Kaaber

530

(Kaaber, 1971b) and stored in closed nolvethvlene containers. Thirty minutes before the experiments, the container was weighed on a micro-balance (Mettler MS) with a reading accuracy of 2pg. Jmmediately after sampling, the disc was transferred to its container, which was reweighed about 60 mm later. Correction for evaporative loss during the transport was assessed according to theoretical values, and calculated on the basis of room temperature, relative humidity and length of the transfer period (Kaaber, 1971a). After the second weight determination, 6OOfl 15 mm01 LiCl were ad&d to the container. After about 20 h elution, the content of Na and K was determined with a flame photometer (IL model 143), using lithium chloride as internal standard (Bofing, 1964) The instrument was adjusted to a standard containing IOmmol Na and K/We, diluted 1:200, and the reading range was increased fourfold The sodium and potassium concentrations of the sample were calculated according to the following formula: (R - BI) x 0.25 x 3OOO/(W+ Ev) = concentration of cations in meq/kg where R is the reading value for either Na+ or K+, W the sample weight change. El the reading value for the corresponding blind sample, and Eo the calculated evaporative water loss during sampling. The accuracy of the determinations was checked as follows: Six serum samples with Na and K coatents of 132-Wmeq/litre and 4.0-8.7meq/litre, respectively, were transferred to the filter-paper discs in aliquots of 400 or 500nl with a micro-syringe (Hamilton type 7001) and thereafter treated like the secretory samples. The mean recovery value in three series of 10 containers at each concentration level was 110 -+ 3 per cent for Na and 90.6 f 6.1 per cent for K. RESUL’IS The amount of Na and K, which together with their anions represent more than 90 per cent of the

osmotically active substances in gastro-intestinal mucous (Gamble, 1954), exhibited a broad range in the pafatal secretion. The great majority of samples were hypotonic compared with the plasma value of 0.300 osmol/litre. However, hypertonic samples were observed after each stimulation, being more frequent in some subjects and after repeated stimulation (Table 1). The ionic concentrations of the latter samples in Table 2 implied that hypertoaicity following initial stimulation was mainly due to a high potassium concentration in samples at a low secretory level, whereas after repeated stimulation it was caused by elevated sodium concentrations, being apparently independent of the secretory stage. Steady state concentrations

Table 1. Tonicity in human palatine secretion after continued

Subjects

of sodium

md potassium

The relationship between Na concentration and the secretory drop size during the first and the subsequent stimulations was studied after excluding the samples in Table 2 with a grossly elevated Na content. A clear trend to a linear relationship was observed in the 500-1250 N area where the mean concentration was 84.3 f 25.4meq Na/kg stimulated secretion and 85.9 f 22.8 meq Na/kg m-stimulated secretion (Pig. 1A) The trend towards a lower Na coatent in re-stimulated samples weighing less than 750~ was significant in the 250-500 erg area (p < 0.10) but not in the 5W750~ area (p < 0.40) The corresponding relationship between the K coatent and drop size in Fig 1B included the elevated values in Table 2. Potassium concentration was in& pendent of drop size when its weight exceeded 500 c1& where it showed a mean value of 14.5 f 4.8 meq K/kg for stimulated secretion and 15.9 f 3.8 for restimulated secretion. Below 500% the K concentration rose, 6rst slightly and then steeply, to a level of about 90 meq/kg secretion for drops weighing below 200 m The three samples with an extremely low electrolyte content (13-15 meq Na and l-3 meq K/kg in a drop weighing between loo0 and 2000~) which were found in one subject among samples with an elevated stimulation

Second stimulation Third stimulation First stimulation Number of Hypotonic Hyper- Number of Hypotonic Hyper- Number of Hypotoaic Hypersamples /isotonic tonic tonic samples /isotonic tonic samples /isotonic

HCd* MHS’ PPcI MGd JW

5 8 7 ; 6

5 8 2 6 5

TMs J-CQ Gf-Q GS’-, HNP JPV L-f-9 GJQ Total %

2 : 2 2 12 4 2 55 100.0

: 2 2 1 12 2 2 ;;7

* Sampling during two experiments.

1

7 6 2 2 5

6 6

2 2 ;

2 2 2 1 6

1 6

1

4 3

4

2 2 2

1

2 2 2 2

3 8.3

15 100.0

10 66.7

3

1 : 5

2

2 4 7.3

36 loo.0

33 91.7

5 33.3

Sodium and potassium in palatine gland secretion Table 2. Ionic concentrations

in hypertonic palatine gland secretion Sample size (S)

Persons

100 First stimulation

L-T I-IN IL FP HC ZZI

Second stimulation

Sl? 1990 450 690 1760 430 440 1490 2270 2810

I-IN I-IN MH MH

Third stimulation

531

‘Na’ (m&g) 118 123 180 156 135 244 170 316 171 762 367 292

cK+ (mesflrs) 89 48 17 7 29 29 22 47 14 20 12 12

electrolyte content indicated the existence of individual aberrant trends

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DISCUSSlON

Secretory activity of palatine glands is stimulated by both tactile and gustatory impulses ((dstlund, 1954; Butcher and Mitchell, 1967; Hensten-Pettersen, 1975). Whether the secretion also takes place under resting conditions has not been completely established, although the glands are capable of secreting spontaneously under in-vitro conditions (0stlund 1954). After gradual elimination of stimulation, Schneyer (1956) found that the secretions of major salivary glands fully accounted for the total volume and that the minor glands secreted only in response to m&.x stimtdation. Dawes and Wood (1973a) found, however, that the minor salivary glands contributed about 6-10 per cent of both resting and stimulated saliva, but their method did not permit any evaluation of the relative contribution of palatine secretion. In my study, no signs of a resting secretion were observed, and the glands seemed to secrete only in response to the tactile stimulation mechanism used. When a previously resting glandular area was stimulated, droplet formation usually occurred very fast, rising in less than 10s up to ~OOOB, thereby indicating a high secretion pressure and a consequent initially high flow rate. Then the flow seemed to slow down, judging from the increase in the droplet size; as the secretory cycle in most instances lasted only about one minute, it was not possible to make a proper estimate of the flow rate. Thus, the samples represented secretory material from different flow-rate levels, and a more thorough analysis of the interrclationship between electrolyte content and flow rate could not be accomplished The great range in their Na content seemed, however, to indicate a positive correlation between the Na concentration of the secretion and the flow rate, as in the large salivary glands (Burgen and Emmelin, 1961; Dawes, 1974). The palatine gland secretion differed, however, by having a far higher mean Na content, the steady state vaiue of about 85 me-q Na/kg secretion being 2-4 times higher than the stimulated values for the large salivary glands (Chauncey et nl., 1966; Dawes, 1969. 1974) and about twice the values observed in lip gland secretion @awes and Wood, 1973b). The potassium

+i-+++&_._____~___~ ._,.,_,......_._._.....................,,..,..... ?..........*......I . SECRETION

AFTER PRIMARY

0 SECRETION

AFTER SUSSEWENT

STIMULATION STIMULATION

.O

N:l

3 3

N : 7 - 17

Fig. 1. Ionic concentration in secretion from human palatine glands A. Relation between the secretory drop size and its sodium concentration in samples obtained after initial and repeated mechanical stimulation. B. Corresponding relation for the potassium concentration of the samples Observed (-) and anticipated (------) course of the ionic concentration values compared with the corresponding plasma value (..........).

532

S. Kaaber

content in the palatine secretion, which exhibited a steady state level of about 15 meq K/kg secretion (Fig. IB), was in the same range as in the other types of salivary gland secretion. The material exhibited distinct signs of transient increases in both Na and K content of the samples. Potassium transients were found only in samples representing the initial stage of the stimulated secretion (Fig. 1B) and were thus in accord with the transients described by Burgen and Emmelin (1961) for various types of animal saliva and recently also for human submandibular saliva (Wiesmann et al.. 1969; Dawes 1974) and parotid saliva (Shannon et al., 1974). This phenomenon has been discussed in detail by Petersen (1972). Evidence for a similar positive sodium transient seemed to be present in the initial part of the previously resting secretion (Fig. 1A) where a significant increase was found. This finding may imply that the sodium re-absorption mechanism of the palatine glands is activated with some delay, as suggested by Petersen and Paulsen (1967) for the cat submandibular gland A more unexpected observation was the presence of several samples with an anomalous high sodium content, occurring after repeated stimulation (Table 2 and Fig 1A). As the K content of these samples was within the normal range of the material (Table 2). it seems unlikely that the transients represent artifacts due to evaporation prior to sampling Their restricted occurrence after repeated stimulation rather implies that they are real and indicative of a Na secretion mechanism of the gland Quantitatively this mechanism was comparable with that located on the stromal side of cornea1 epithelium. where similar transients of 400-f3OOmeq Na/ litre have been reported (Green. 1970). At any rate, these observations may support the idea of a Na pump located at the luminal membrane of the acinar cell, as proposed from electrophysiological studies of the submandibular gland (Petersen, 1972b; Imai, 1976). The sparse knowledge of the structure and secretory function of the palatine glands and problems of obtaining samples of secretory material at de&red flow rates for quantitation at present prevent a more detailed discussion of the results The observations show, however, that the secretion, due to its high tonicity compared with the other types of salivary glands, forms an intermediate link with the mucous glands of the gastrointestinal tract in which an isotonic secretion is produced maysen, 1960) REFERENCES

Boling E. A. 1964. A !lame photometer with simultaneous digital read-out for sodium and potassium J. L.ab. cfin. Med. 63, 501-510. Bumen A. S. V. and Emmelin N. G. 1961. Physiology of _ -_ t& Saliwry Glands. Arnold London. Butcher E. 0. and Mitchell 0. G. 1967. Structure and secretory mechanism of rodent and primate palatine glands J. dent. Res. 46, 672-674.

Chauncey H. H., Feller R. P. and Henriques B. L. 1966. Comparative electrolyte composition of parotid submandibular and sublingual secretion. J. dent. Res. 45, 1230. Dawes C. 1969. The effect of flow rate and duration of stimulation on the concentration of protein and the main electrolytes in human parotid saliva. Archs oral Biol. 14. 277-294.

Dawes C. 1974. The e&t of flow rate and duration of stimulation on the concentrations of protein and the main electrolytes in human submandibular saliva. Archs oral Biol. 19, 887-985.

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