Eump. J. clin. Invest. 2, 398-406 (1972)

Mono- and Divalent Electrolyte Patterns, pC02 and pH in Relation to Flow Rate in Normal Human Parotid Saliva*

W. Kreusser, A. Heidland, H. Hennemann, Department of Internal Medicine, University of Wiirzburg

M. E. Wigand **, Department of Otolaryngology, University of Wiirzburg

and H. Knauf*** Xax-Planck-Institute for Biophysics, Frankfurt a. &I,

Received: March 2, 1972

Abstract. In parotid saliva of normal subjecta the pH, pC0, and concentratione of sodium, potassium, calcium, mqneaium, bicarbonate and inorganic phosphate were deter- mined continuously after stimulation of salivary secretion by pilocarpine. The electrolyte concentrations showed a marked dependence on salivary flow rate. Sodium, calcium and bi- carbonate concentrations and pH increased with increasing flow rate but the concentrations of potaasium, magnesium and inorganic phosphate decreased with increasing flow rate. In general salivary electrolyte concentrations showed a

tendency to approach plasma concentrations with increasing flow rate with the exception of the salivary magnesium con- centration, which fell below its plasma level and bicarbonate which exceeded the plasma concentration. The results will be considered a.s e basis of further investigations on electrolyte excretion patterns in patients with hormonal and metabolic disturbances.

Key wok: Human parotid gland; excretion of the cations sodium, potaasium, calcium and magnesium; excretion of the anions bicarbonate and inorganic phosphate.

Thaysen et al., [20] were the first to assume a two- stage-production of saliva: At the first stage the acinar epithelium produces a precursor fluid in a quantity proportional to the salivary flow rate. At the second stage sodium ions are partly reabsorbed during their passage along the glandular duct system.

The adaptation of micropuncture techniques to the salivary glands of the rat showed the primary secre- tion to be almost plasma-like with regard to osmo- larity and the concentrations of Na+, K+ and C1- in the submaxillary [%I, parotid [13] and sublingual glands [li]. A similar primary secretion was found in sweat glands [18] and pancreas [19]. It was demon- strated that the changes of electrolyte concentration observed in the final saliva occur only during the passage of the fluid along the duct system. I n micro- perfusion experiments (Young et al. [25, 271) it was demonstrated that the epithelium of the submaxillary duct system is capable of reabsorbing Na+ and of secreting Kf and HCO; by means of an active trans- port mechanism.

In micropunction and microperfusion experiments on rat submaxillary glands Young and Martin [la, 281 could show that both sympathomimetic and para- sympathomimetic b g s stimulate the electrolyte secretion of primary saliva. Furthermore both auto- nomic drugs act directly on the duct epithelium to promote secretion of potassium and bicarbonate. * Supported by the Deutsche Forschungsgemeinschaft, Bad

Godesberg. ** Preaent address: Department of Otolaryngology, Univ. of Erlangen-Niirnberg. *** Present address: Department of Internal Medicine, Frei- burg i. Br.

Parasympathomimetics are more effective than sym- pathomimetics at the primary level (acinar epithelium) but a t the ductal level the two drugs have similar actions and, when administered together, the effects are additive.

In the human parotid, submaxillary and sublingual glands, Knauf and Fromter [S] have recently demon- strated and mathematically evaluated the dependence of salivary sodium and potassium excretion on flow rate. The sodium concentration of final saliva of all three glands increases exponentially with increasing flow rate and tends to asymptote to plasma-like levels at infinitely high flow rates.

Salivary Kf concentration, however, declines with increasing flow rate towards almost constant values which are about three times the value of plasma K+ concentration. Thus, salivary K+ excretion increases almost linearly with salivary flow rate [8, 201.

Our knowledge about the excretion of divalent cations and the anions bicarbonate and inorganic phosphate, however, is comparatively poor. The es- cretion pattern of magnesium and calcium has recently been studied in the submandibular gland of the cat by Nielsen and Petersen [15]. I n humans, studies on the excretion pattern of divalent cations led to dif- ferent results. This might be due either to unspecific analytical methods [i, 2, 5, 6, 121 or to differences in the salivary collection methods. Furthermore the flow rate dependence was neglected [5, 61. More reliable information about the divalent cations was published by Dawes [3]. He used a specific analytical method (atomic absorption spectrophotometry), and measured flow rates. The studies, however, were

W. Kreueser et al.: Xono- and Divalent Electrolyte Pattama 399

limited to low rates of flow (up to 1 ml/min). More- over, the studies were aimed primarily at proving the dependence of electrolyte concentration on time a t constant flow rates. The flow dependent changes were not continuously correlated.

As in the case of magnesium and calcium, there exist only a little reliable data about the salivary excretion of inorganic pk ipha te [23]. Usually the flow rate was not regarded as a parameter. However, it seems generally accepted that for the main human salivary glands, an increase in flow rate from the resting level is accompanied by a decrease in the concentration of inorganic phosphate in each of the separate secretions [2].

The data for the parotid bicarbonate excretion were obtained either in normal subjects with low flow rates only [l, 41 or in hypertensive individuals

The present paper deals with the flow dependent excretion patterns of the main electrolytes of the human parotid gland. Special attention is paid to the divalent cations and the anions bicarbonate and in- organic phosphate.

Methods The experiments were performed in 20 fasting

students (20 to 27 years old) between 8 and 10 a.m. under standardized conditions : The healthy volunteers received the same food from a students mess, contain- ing on average 160-200 mEq sodium and 60-80 mEq potassium per day. The saliva was sampled with the students resting in supine position from' 30 minutes before the first sample to the end of the experiment. For the collection of saliva a thin polyethylene ca- theter w- inserted 20-30mm into Stensen's duct with two spindle shaped pads tightening the relatively narrow duct-opening. Thus any risk of dislodgement of the catheter could be avoided. An exchangeable polyethylene vessel of calibrated volume (300 4) was connected to the collecting tube, and the salivary flow rate was determined by measuring the time required to obtain a 300p.l sample. The production of saliva was stimulated by a subcutaneous injection of pilocarpine (0.06mg/kg body weight) and, if necessary, by additional adminiRtration of lemon juice on the tongue. Thus, under optimal circum- stances up to 50 samples could be obtained within 1 hour.

Sodium and potassium were determined simul- taneously using flame photometry (Eppendorf); mag- nesium and calcium concentration were measured by atomic absorption spectrophotometry (Beckman) ac- cording to the analytical procedure of Gow [7]. Strontium chloride (10 P.c.) was used for the dilution of the stock-solutions. The standard solutions were stored in polyethylene vessels.

For the samples in which pH and pC0, were measured the saliva was collected in separate capillary tubes and closed with kneading gum to avoid gas ex-

[201-

change. In control studies it could be shown that knead- ing gum is suitable to prevent a measurable loss of CO, within the time of analysis. The calculation of bicarbonate concentration was performed using the Henderson- Hasselbalch equation :

The actual salivary pH and pC0, were measured directly using the glasa electrodes of a micro-Astrup device (according to K. Harnoucourt). The absorption coefficient of carbon dioxide a (measured as ml gas which is soluble in 1 ml solution a t a partial pressure of 760 mm Hg and a temperature of 38 "C) is 0.5087 in plasma and 0.5439 in water (quoted by Uhlich et al. [21]). Expressed in milliequivalent CO, per litre and mm Rg the value is 0.0302 for plasma and 0.0322 for water.

The pK' value was assumed to be constant at 6.187 thus :

pK' was calculated by the formula pK'=pK-Afi. The constant A is given in the literature (quoted by Uhlich et al. [21]) as 0.522 in aqueous solutions and as 0.502 in plasma. The ionic strength (p) was cal- culated using the formula= 1/2 E c c i . z : where ci re- presents the concentration of the ion in a solution and zi is its valency. According to our results the ionic strength varies in the saliva from 30mM at a flow rate of 0.1 ml/min. to 104 mM at 3 ml/min. The pK' value changes from 6.213 (flow rate 0.1 ml/min.) to 6.162 (flow rate 3.0ml/min.). These changes, of at most five hundredths of a unit of p K , would not affect the bicarbonate concentration appreciably.

The determination of inorganic phosphate was performed by a modification of Raabe's method [17] using Mercko-Test reagents. The pH dependent forms of mono- and dihydrogen phosphate were calculated using the Henderson-Hasselbalch equation

Since the salivary pH varies between 5.6-8.0, the second dissociation constant of phosphoric acid pK,=7.165 was used and pK; was assumed to be constant at 6.80 as explained above for carbonic acid.

Chloride was not measured in our studies. How- ever, its concentration was estimated as the difference between the sum of the cations (Na+, K+, Ca, Mg) and the sum of the anions bicarbonate and inorganic phosphate, because other ions do not contribute appreciably to the osmolarity of saliva.

The above mentioned saliva electrolytes were memured in the plasma of the volunteers. The pro- tein-bound and protein-free fraction of calcium and magnesium were determined by ultrafiltration of the serum through 8/32 inch Visking tubings a t 38 "C according to Petersen [16].

The amount of sodium, which is actively reabsorbed by the total glandular duct system was calculated as follows :

400 W. Kreusser et al.: Mono- and Divalent Electrolyte Patterns Europ. J . din. Invest.

N o r m a l S u b j e c t

I

I . o a 16 2.4 32 LO ~8 56

Time after stimulationlminl

Fig. 1. Time course of flow rate and electrolyte concentrations of parotid saliva in a normal subject before and after stimula- tion with pilocarpine. The delay of the maxima or minima of electrolyte concentratiom, compared with the flow rate maximum, is illustrated by the broken vertical lines. Thia is caused by the dead space of the glandular duct system

According to Eq. (14a) in ref. [8] the Naf concen- tration in final saliva (c) is:

~ J: e-p. .!. . P* J .

where JZ (mEq/min.) represents the maximum amount of sodium which can be actively reabsorbed by the total glandular duct system per minute. P* re- presents the passive leak permeability of the epi- thelium for Na+ (mlimin.). I'* is proportional to the passive back flux of Na+ from the interstitium to the lumen. When salivary flow rate (4,) becomes infinite c obviously becomes

J:, ( C ) J * - = C" = -p* .

As shown by Knauf and Frijmter [S j C, equals plasma Na+ concentration as postulated by the mathematical model. For the determination of the parameters JZ, P* and C,, the logarithm of Na-+ concentration of collected saliva is plotted against the reciprocal of flow rate. As can be derived from the above equation P* is the slope of the exponential regression line and C, is the salivary Na+ concentration extrapolated to infinite flow rates. Finally JZ = c,, x P*. (For details see P I . )

The samples obtained during the increasing se- cretion phase were not taken into account, because contamination of unstimulated with stimulated saliva in the duct system must be expected. This would hamper a true correlation between ion concentration and flow rate (for details see Knauf and FrBmter [Sl).

Results and Discussion In our investigations on salivary electrolyte pat-

tern in 20 normal adults only the data obtained from individuals with flow rates of more than 1 ml/min. were used. This was the case in 13 students. Two of them revealed an abnormal electrolyte pattern and will be discussed in the last section. In 7 students the salivary flow rate was less than 1 ml/min. Their data were excluded from our graphical and mathe- matical processing because our interest was centered on high flow rates (more than 1 ml/min.). Further-

Table 1 . Salivary electrolyte concentration and the standard deviation (S.D.) at defined flow rates in normal subjects: Flow rate 0.1-1.0 d/min (n = ll), 2 ml/min (n = 8), 3 ml/min (n = 5)

Salivary electrolytes (m-Em 0.1 0.5 1.0 2.0 3.0

Salivrq flow rate (ml/min)

Sodium Potmaium Calcium Magnesium Total cationa (mean values)

2.5 hO.45 19.4h2.12 18.5 h l . 2 2 16.3k1.74 1.8 10.21 2.3 h0.32 0.22k0.05 O.lO&O.O3

23.02 38.10

Bicarbonate Inorganic phosphate k t of anions

4.6 10 .96 19.6 k3.91 7.8 +0.92 7.2 rfrO.81

11 11

41.4f4.40 74.6h5.10 83 .91 7.38 13.311.29 13.010.87 12.8k0.83 2.6 10 .31 2.8 k0.34 3.0 hO.50 0.07 f0.03 0.06 k0.02 0.06 & 0.01

57.37 90.46 99.76

34.0 k4.43 51.0 17 .57 59.0 h5.71 6.5 1 0 . 9 0 5.9 50.83 5.8 kO.77

17 34 35

Vol. 2, No. 6, 1972 W. Kreusser et al. : Mono- and Divalent Electrolyte Patterns 401

Cat ions n = 5

Monova I e n t Divalent

* .

,o{ I [ Naf] : . . . . . ." . . . _ _ I I . . . 601 I . . :. . :. . . . . .

" I I . r r 7 r - . ,- 0 1.0 2.0 *3.0

Flow rate [ml /rnin]

6.0 r- \

= o E

0.4

0.2

0

W

U

0 1.0 2.0 3.0 Flow rate[ml/min]

Fig. 2. Flow-concentration-relationship of the mono- and divalent cations after stimulation with pilocarpine in 5 healthy subjects. The values before zero flow rate represent the electrolyte concentrations of the resting state. With increasing flow rate

the concentration of sodium, and--to 8 smaller extent-of calcium rises, whereas the concentration of potassium and magnesium decreases

more a flow rate of more than 0.7 ml/min. is a prere- quisite to the calculation of JZ [8].

I n Fig. 1 the time course of the salivary flow rate and the concomitant changes in the electrolyte con- centrations of one individual are given. The flow rate reached its maximum 8-10 min. after stimulation and then sloped asymptotically back to the starting values within 40-60 min. The curve of Na+, Ca and HCOj concentration paralleled that of the flow rate and showed maximal values 10-12 min. after stimulation. At the same time the concentration of K+, Mg and inorganic phosphate minimalized. The delay of the maximal or minimal electrolyte concentrations in comparison to the flow rate maximum is due to the dead space of the duct system.

The flow rate dependence of electrolyte concen- trations of the 11 subjects studied are given in Table 1. I n Fig. 2 , 4 , 5 and 6 the values of 5 volunteers whose salivary flow rates reached more than 2.5 ml/ min. are given.

Salivary Cations sodium

The Na+ concentration was found to be 2.5f 0.45mEq/l a t low flow rates (0.1 ml/min.) and 83.9 & 7.38 mEq/l a t high flow rates (3.0 ml/min.).

I n Fig. 2 the flow rate dependence of the mono- and divalent cations of 5 individuals with flow rates higher than 2.5 ml/min. is demonstrated. I n these cases the electrolyte concentration is plotted against the flow rate. According to earlier results [a, 8, 201

the curve of Na+ concentration in the final saliva increases with increasing flow rate in an almost exponential slope.

In Fig. 3 the Na+ concentration of a typical example is plotted in a logarithmic scale against the reciprocal flow rate. This graphic diagram allows extrapolation of the salivary Na+ concentration to infinitely high flow rates (c,,) and thereby calculation of the amount of Na+ actively reabsorbed by the duct system (JZ). For the 11 students JZ was calculated to be 17lfl2pEqlmin. per gland. P* was deter- mined to be 1.25 f 0.07 mllmin. These data represent mean values f S.D. Our data agree well with those reported by Knauf and Frtimter [8]. They are about three times higher than those reported by Thaysen et al. [20].

Potassium The K+ concentration in the final parotid saliva

a t the lowest flow rates was measured and found to be 18.5 f 1.22 mEq/l (Table 1). With increasing flow rates the concentration decreased, but always re- mained at levels about three times the plasma values. With flow rates exceeding 1.0 mllmin. I<+ concentra- tion remained practically constant a t about 13 mEq/l (see Fig. 2). Therefore the potassium excretion in- creases linearly with increasing flow rate. Similar findings were published by others [8, 201.

Calcium Salivary Ca concentration was found to be 1.8f

0.21 mEq/l a t low rates of flow (0.1 mljmin.) (Table 1).

402 W. Kreusaer et al. : Mono- and Divalent Electrolyte Pattern9 Europ. J . din. Invest

Normal S u b j e c t

R. A. d 27 Y.

Na' 1 J & = 166(@q/minI P * 1.20 (ml/min) CO = 138(mEq/i)

(mEq/l)

200

1 o o h

2oj lo \. .- . 2 I \ 1' 0 1 2 3 L 5 6

l/Flow rate [min/ml] Fig. 3. Salivary sodium concentration (in a logarithmic scale) plotted against the reciprocal of flow rate (according to Knauf and Friimter [S]). At flow rates above 0.7 ml/min. the pointa form a straight line, which at endlesa flow ratea cub the ordinate in the height of the corresponding plasma con- centration (C$J..J:, represents the total amount of sodium, actively reabsorbed by the duct system. P* corresponds to its

leak permeability

A t a flow rate of 3.0ml/'min. the Ca concentration was 3.0 f 0.50 mEq/l (see Fig. 2). Hence, calcium showed a similar flow-concentration relationship to sodium. It should be emphasized, however, that the calcium concentration was almost maximal a t a flow rate of 1.0 ml/min., while a further increase did not give a significant rise. A t flow rates above 1.0 ml/min. the Ca concentration sometimes surpassed the concen- tration of the ionized plasma calcium, which normally ranges from 2.5 to 3.0mEq/l. According to Vogel, Naujoks, and Brudevold [23] the ionized Ca concen- tration in the final saliva of the human parotid gland is only one half of the total calcium concentration. Therefore, if in the primary acinar secretion the ionized Ca concentration is identical with the corre- sponding plasma value, then we have to assume a net reabsorption of calcium by the duct epithelium. Micropuncture studies on ionized Ca concentration in the primary saliva, however, are still lacking.

In our studies the total calcium concentration a t defined flow rates was higher than that reported by Dawes [3]. In contrast to our analysis Dawes used lanthanum chloride instead of strontium chloride to dilute the samples. LaCl,, however, is known to con- tain a certain amount of calcium, which may have influenced his blank readings.

I n the submaxillary gland of the cat, however, the salivary calcium excretion pattern is different from that in human parotid. The calcium concentra-

tion of the cat submaxillary saliva decreases with increasing flow rate (Nielsen and Petersen [15]). We do not know whether this different Ca excretion is due to differences in the gland types or in the species.

Magnesium Salivary magnesium concentration showed a nega-

tive correlation to the flow rate (Fig. 2). At low rates of flow (0.1 ml/min.) the average concentration was 0.22 f 0.05 mEq/l (Table 1). This concentration de- clined with increasing salivary flow rate, and reached nearly constant values of 0.07-0.06 mEq/l between 1.0-3.0 ml/min. I n the low flow rate area lower concentrations have been published by Dawes using the atomic absorption spectrophotometry [3]. How- ever, much higher concentrations were found in magnesium determinations with colorimetric methods [6]. Compared to the plasma level of ultrafiltrable magnesium, which was determined to be 1.22& 0.25 mE41 in our laboratory, the salivary magnesium level was considerably lower a t all flow rates. For this finding two explanations are possible: If we assume the concentration of magnesium in the primary saliva of the acini t o be identical with the ultra- filtrable plasma Mg concentration, a reabsorption of magnesium by the parotid duct system might occur against both a concentration difference and an electrical potential difference [gal. The low ma- gnesium levels in final saliva a t high flow rates must then be interpreted as an increased reabsorption with increasing flow rates. This speculation implies that the magnesium reabsorbing process is stimulated proportionally to the flow rate.

The following explanation seems to be more probable. If the acinar epithelium is poorly permeable to magnesium ions, as is, for instance, the frog skin [22], then magnesium might enter into the saliva through the epithelium of the duct system. From the similarity between magnesium and potassium concen- trations as functions of flow rates it might be inferred that magnesium is secreted by the glandular duct epithelium as it is the case for K+ ions. We may stress, however, that similarities in concentration- flow-rate-pattern per se do not allow conclusions about the underlying transport mechanisms.

Salivary pH and pC0, At the resting state the salivary pH values aver-

aged 5.8. After stimulation a rapid increase was observed, which a t higher rates leveled off to a pH of 7.80 (Fig.4). Similar values were published by Dawes [2, 41.

The pC0, varied between 35 f 2 mm Hg a t low rates of flow and 39 f 3 mm Hg a t a maximal salivary secretion rate (Fig. 4). Our salivary pC0, values figured within the range of the pC0, in the capillary blood, which averaged 36 f 3 mm Hg in our study. The low salivary pC0, may be partly due to a loss

VoE. 2, No. 6, 1972 W. Kreuaser et al.: Mono- and Divalent Electrolyte Pattern 403

of CO, via the catheter opening during prolonged collection time a t low flow rate. In no instance did we observe a pC0, of more than 50 mm Hg as men- tioned by Dawes [4] in single subjects.

Salivary Anions Bicarbonate

The calculated RC06 concentration (Fig. 4) was extremely low in the resting state (< 1 meq/l) and a t low flow rates after stimulation. With increasing flow rates (up to 1.5ml/min.) an almost linear rise of bicarbonate was observed. At higher flow rates the slope of the curve flattened. With a maximal flow rate (3 ml/min.) the concentration of HCO; reached a level of 59 f 6 mEq/l, thus exceeding the plasma level by more than twice.

Thaysen et al. [20] found higher E C O i levels a t low flow rates than we did. We cannot decide whether this difference is due to the method of examination, or to the selection of the individuals. The data of Thaysen et al. [20] were based on findings in hyper- tensive patients, who could have an increased sym- pathetic tonus, which may influence the salivary electrolyte concentrations [14, 281.

The finding of a HCO, concentration difference between lumen and interstitium a t high salivary flow rates and the electrical potential difference (negativity of the lumen as compared to the interstitium [gal) support the assumption that ductal HC06 transport is an uphill secretion by the duct epithelium. An active HCO; secretion by the duct epithelium has already been shown in rat submaxillary glands by means of microperfusion experiments [27].

From previous studies we know (Knauf and From- ter [gal) that the electrical potential difference is about 40mV (lumen negative) a t the resting state. Obviously, bicarbonate is in electrochemical equili- brium in the resting state of the gland as can be inferred from the N e m t equation when inserting salivary and plasma HCO; concentration (- 40 mV = R T - log $). We know already from microperfusion F studies in rat submaxillary glands (Martin and Young, 1971 [14, 281) that sympathomimetic and parasym- pathomimetic drugs stimulate HCOi secretion on the ductal level. From our findings we may awume that HCO; is actively secreted by human parotid duct epithelium, too, and that in the absence of stimulants (resting state) HCOg is passively distributed across the duct epithelium.

Inorganic Phosphate The salivary concentration of inorganic phosphate

(mM) is plotted against flow rate in Fig. 5. The total concentration showed highest values of 10 mM in the resting state ; after stimulation the phosphate concen- tration was reduced with increasing flow rates. At flow rates exceeding 0.75 ml/min. the concentration

..-

P co, ................ ........ ....* 1' . . .

:* .... ..::.:.: . . . .......... . . . . . . ::: - :. - . .......

* * . * . .

. . ...... t. . . . . . . . .

0 1.0 2.0 3.0 Flow rate [mI/min]

Fig. 4. Dependence of pH, pC0, and the concentration of HCO; on the salivary flow rate in 5 normal subjects (salivary stimulation with pilocarpine). The HCO; concentration was calculated by the equation of Henderson-Haaselbalch. With increasing flow rates there is a rapid rise of pH and HCO; concentration and a tendency of pC0, to increase. "he values obtained during the resting state are given before zero flow rate

was about 3 mM and seemed to be relatively in- dependent of flow rate. This observation is in good agreement with the findings of Dawes and Jen-

At the salivary range of pH between 5.6-7.8 the total concentration of inorganic phosphate is formed by mono- and dihydrogen phosphate. The calculated values of these two forms showed a different pattern: In the resting state the concentration of &hydrogen phosphate averaged 7.8 mM, whereas monohydrogen phosphate averaged 1 mM. Salivary stimulation induc- ed a rapid decrease of dihydrogen phosphate, and a simultaneous increase of monohydrogen phosphate as a consequence of the rise of the salivary pH. At

kins [Z].

404 W. Kreiwer et ul.: Mono- and Divalent Electrolyte Patterns Europ. J. din. Invest.

CmMl 10

6

2

r

I

0 1.0 2.0 3.0 Flow rate [ml/min]

Fig. 5. Flow rate dependence of total inorganic phosphate and the different fonns of inorganic phosphate at the corresponding pH-values after stimulation with pilocarpine in 5 healthy subjects. The concentrations of mono- and dihydrogenphoa- phate are calculated according to the Henderson-Hctaeelbalch equation. The values before zero flow rate were obtained in

the resting state

80

60

40

20

0

I I ... !

60

A n i o n s n=5

Pinorg.

I 1 I . 0 10 20 30

Flow rate [ ml /min] -

Fig. 6. Flow-concentration-relationship of the anions bicarbo- nate, inorganic phosphate and the fraction of the remaining anions (Cl-) after salivary stimulation with pilocarpine in 5 healthy subjects. The remaining anions are calculated from the difference between the sum of cations and the sum of the anions bicarbonate and inorganic phosphate. The phosphate concentration aa mEq/l represents the loadings. With in- creasing flow rate the concentration of HCO;;, and-to a smaller extent-af GI- increases, w h e w the concentration of

inorganic phosphate decreases

Dawes [4] this increase is limited to a low flow rate (< 0.75 ml/min.).

I n Fig. 6 the inorganic phosphate concentration as mEq/l is given, as calculated by the mono- and di- hydrogen phosphate. The flow dependent decrease is less pronounced than in Fig. 5, where inorganic phos- phate is expressed as mM. This is caused by the fact, that at a low pH (and a low flow rate) the total

flow rates above 0.75 milmin. and a pH above 7.5 the concentrations of both forms of phosphate were nearly constant.

In the studies of Vogel, Naujoks, and Brudevold [23] the salivary excretion pattern of monohydrogen phosphate showed a tendency to increase with higher flow rates. According t o our results and those of

V O l . 2, No. 6 , 1972 W. Kreusser et al. : Mono- and Divalent Electrolyte Patterns 405

concentration exists mainly in the monovalent form and only to a small part in the divalent form, by which the number of loadings is relatively reduced.

At any given flow rate the total salivary phosphate concentration exceeded the corresponding plasma con- centration considerably. This finding, as well as a similar flow rate dependence to that of potassium, suggests a secretion of phosphate by the salivary duct epithelium. The underlying mechanism is so far unknown.

Since a t high flow rates the phosphate concen- tration in final saliva is much lower than the HCO; concentration the buffer system of mono- and di- hydrogen phosphate is less important. The phosphate buffer may, however, play a role in the resting state of the gland and a t low flow rates, when phosphate concentration exceeds that of HCO;.

Chloride The CI- concentration was calculated as the fraction

of the remaining anions. A t a flow rate of 0.1 ml/min. we calculated the concentration to be 11 mEq/l, a t a flow rate of 3 ml/min. the concentration averaged 35 mEq/l (Fig. 6, Table 1). Thus the concentration of the remaining anions showed a flow dependent in- crease, which resembles the data of Thaysen et al. [20], and Dawes [4] for parotid C1- concentration.

So far the handling of chloride by the duct system was only studied in the rat submaxillary duct using microperfusion techniques (Young [as]). In this organ chloride was found to be passively distributed. As for the human parotid duct a passive handling of chloride is probable, but further studies combining analytical and electrical measurements are needed.

In our numerical and graphical evaluations the results of two normotensive students, who exhibited marked vegetative symptoms (hyperhydrosis, tachy- cardia, dermographism) were disregarded. Both per- sons showed extremely low sodium concentrations of maximal 25-30 mEq/l in spite of high salivary flow rates of about 2 ml/min. Similarly, their bicarbonate concentration was reduced. Potassium, inorganic phosphate, calcium and magnesium showed normal values. An aldosteronism which is known to increase salivary sodium reabsorption [lo] could be ruled out insofar as in both persons neither the applications of spironolactone (150 mg Aldactone@SO at each of 3 days) nor salt load (10 g NaCl a t each of 4 days) influenced their electrolyte patterns. The reason for this abnormal secretion pattern is unknown. Similar observations are not published in the current literature.

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parotid gland secretion: Flow rate and interrelationships of pH and inorganic components. Proc. SOC. exp. Biol. (N.Y.) 97,539-542 (1958).

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Prof. Dr. A. Heidiand Mediziiche Universitiitsklinik D-8700 Wiirzburg Federal Republic of Germany