Ionic, histological and vascular factors in the reaction of the sheep's parotid to high and low mineralocorticoid status

An investigation of the vascular organisation of the canine submandibular gland

It is known that parasympathetic nerve stimulation elevates venous pressure in the dog submandibular gland, and that the venous pressure wave is transformed to that of the arterial pulse. The vascular arrangements and histological characteristics of the dog submandibular gland were therefore examined to establish which anatomical structures are responsible for the change in venous pressure during salivation induced by parasympathetic stimulation. The acinar and ductal circulations were found to be arranged in parallel and arteriovenous anastomoses were identified in both. Microsphere injection studies demonstrated the opening of arteriovenous anastomoses in actively secreting glands. Smooth muscle cells were rarely found in venous blood vessels but venous valves were abundant in both circulations. Dense connective tissue was observed to enclose the ductal system and its accompanying structures (blood vessels, lymphatic vessels and nerves); it was most abundant in the hilum and diminished aborally. The mechanism responsible for elevating venous pressure during parasympathetic salivation is thus probably related to opening of the arteriovenous anastomoses; the increase in the amount of surrounding dense connective tissue in a central direction may facilitate the preservation of the transmitted arterial pressure and pulse in the venous system.

Preparation and characterization of basolateral plasma-membrane vesicles from sheep parotid glands. Mechanisms of phosphate and D-glucose transport

A procedure is described for the preparation of basolateral membrane vesicles from the acinar cells of the sheep parotid gland. The ouabain-sensitive K(+)-activated phosphatase activity was enriched 30-fold over the tissue homogenate; 45% of this activity was recovered in the final membrane fraction. The presence of membranes from other organelles was negligible. Evidence is presented for the location of Na(+)-dependent symporters for phosphate and D-glucose on the basolateral membrane.

The pathogenesis of chronic recurrent parotitis in infants: a study of 93 cases including an analysis of the vascular and glandular changes before and after parasympathectomy

Ninety-three cases of infantile chronic recurrent parotitis are recorded. Fifty-three cases were treated with parasympathectomy which was carried out at 2 levels. Good results were achieved in 79.1% of patients. The paper describes the use of the Doppler examination to study the effects of operation on the physiology of the parotid.

A micropuncture investigation of electrolyte transport in the parotid glands of sodium-replete and sodium-depleted sheep

1. Parotid secretion has been studied by micropuncture in sodium-replete and sodium-deficient sheep. 2. The osmolality of unstimulated primary saliva was slightly higher than in plasma and fell following cholinergic nerve stimulation. In sodium-depleted animals the osmolality of final saliva was hypotonic and exhibited flow dependency, where as in sodium-replete animals it was always isotonic. 3. In sodium-replete sheep, the primary fluid sodium concentration was about 120-130 mmol l-1 but in final saliva it was about 167 mmol l-1 and showed little or no flow-dependency. In sodium-depleted sheep, the primary sodium concentration averaged only 82.2 mmol l-1 and it was concluded that sodium-depleted primary fluid contained some other unidentified solute that allowed it to remain approximately isotonic; in final saliva the unstimulated sodium concentration was about 40 mmol l-1 and it rose with increasing flow rate to a maximum of 114.9 mmol l-1. 4. The primary fluid potassium concentration in sodium-replete animals did not differ significantly from that seen in sodium-depleted animals and the values were uninfluenced by stimulation; the over-all mean value was 11.2 mmol l-1. In final saliva, in sodium-replete sheep, the potassium concentrations averaged 7.8 mmol l-1 but in sodium-depleted sheep the concentrations were between 5 and 10 times greater than in primary fluid. 5. It was calculated from the equilibrium pH that the primary bicarbonate concentration would have been about 35 mmol l-1. In final saliva, where bicarbonate was measured directly, the concentrations were much greater and increased with stimulation to about 115 mmol l-1. 6. The primary fluid phosphate and chloride concentrations were the same in both sodium-replete and sodium-depleted animals and were unchanged by stimulation; the mean concentration of phosphate was 1.30 mmol l-1 and of chloride, 53.0 mmol l-1. In final saliva the phosphate concentrations were little changed but the chloride concentrations fell to an average value of 20.0 mmol l-1. In final saliva it was found that the summed sodium and potassium concentrations exceeded the summed chloride, bicarbonate and phosphate (in mequiv l-1) concentrations, on average by 13.9 mequiv l-1, regardless of sodium status or flow rate. 7. The results indicate that secretion by the sheep parotid can be accounted for in terms of the standard two-state model. Phosphate seems to enter the saliva only in the primary fluid and potassium and bicarbonate appear to enter at both primary and secondary sites; sodium and chloride enter at the primary level and can be reabsorbed in the ducts. Salt depletion causes the primary fluid concentrations of sodium and chloride to fall and the content of an unidentified solute to rise markedly while, at the ductal level, it causes normally quiescent sodium and potassium transport processes to become activated.

Gap junctions on myoepithelial cells

In the submandibular gland of the male mouse, myoepithelial cells are found not only located to the endpieces and intercalated ducts, but also around the striated (or granulated) ducts. Irrespective of their location in the gland, the myoepithelial cells and their processes were found to be connected by gap junctions. It is suggested that these gap junctions play a key role in the synchronization of the contractile function of the myoepithelial cells.

The effect of carbonic anhydrase inhibitors on the anionic composition of sheep's parotid saliva. With an appendix on uncatalysed carbon dioxide-water kinetics by P. T. McTigue

1. The effects of the carbonic anhydrase inhibitors, acetazolamide, ethoxzolamide and benzolamide on the ionic composition of parotid saliva were studied in anaesthetized sheep with access to the parotid blood vessels. 2. The inhibitors were infused directly into the arterial blood supply to the gland to give blood concentrations in the range 10(-5) to 10(-2) M. 3. Mean anionic concentrations at basal flow rate before inhibitor infusion were, bicarbonate 98 m-mole/l., phosphate 15 m-mole/l. and chloride 26 m-mole/l. In the presence of inhibitors, bicarbonate concentration fell by 11 m-mole/ml. and phosphate and chloride concentrations rose. Secreto-motor nerve stimulation increased bicarbonate concentration by 13 m-mole/l. before infusion of inhibitors and the concentrations of the other anions fell. The bicarbonate rise was abolished by the inhibitors and the fall in phosphate concentration was balanced by a rise in chloride concentration. 4. These effects show that only a small component of the bicarbonate ion transfer system in the sheep parotid gland is sensitive to these inhibitors. 5. The relationship of these findings to a new enzyme with carbonic anhydrase action isolated from the sheep's parotid gland is discussed.

The metabolic effects of sodium depletion in calves on salt appetite assessed by operant methods

1. Sodium deficiency was induced in calves by unilateral exteriorization of the parotid duct, the continual loss of alkaline saliva from the body to the environment causing negative sodium balance. 2. The metabolic effect of negative sodium balance was seen in statistically significant reduction in plasma sodium and blood bicarbonate, together with marked acidosis and reduced plasma osmolality. 3. The homoeostatic response to sodium depletion was associated with a reversal of sodium/potassium ratio in parotid saliva and a reduction of the rate of secretion. Appetite diminished. The extracellular fluid was halved as marked diuresis developed with considerable weight loss. Urinary and faecal sodium was reduced to zero. 4. On restoration of sodium balance by allowing the calves to drink sodium bicarbonate solutions the metabolic deviations were eliminated. 5. During sodium depletion the parotid gland was able to respond to transient reflex stimulation by increasing flow rate and the sodium concentration of the saliva. 6. When sodium depleted, the calves became restless and agitated and would run from the home pen to the operant procedure stand. The sodium depleted animals readily pressed a panel for sodium bicarbonate rewards in direct proportion to the degree of sodium imbalance. When the balance was restored the motivation to work for sodium bicarbonate disappeared. 7. The motivation which developed during sodium depletion was directed specifically towards the sodium ion. Lithium was an exception to this rule and sodium carbonate was aversive. 8. It is possible that in sodium depletion the glottal sodium taste receptors develop an enhanced threshold for sodium ions because of the reduced sodium content of the saliva. This effect would be abolished when the content of sodium was restored in saliva. 9. The correlation of operant reactions and sodium depletion suggests that the consequential metabolic effects activate changes in the central nervous system. 10. The metabolic changes which develop in parallel with the severity of the sodium deficit appear to be able to evoke behavioural changes with increase in salt appetite directed towards restoration of sodium balance.

The organization of the salivary gland microcirculation

1. The microvasculature of the rabbit submandibular salivary gland has been investigated employing in vivo microscopy, blood flow measurements, latex casts, microsphere injections and examination of fixed sections of the gland.2. Two principal microcirculations were distinguished in the living gland, one supplying the acini and the other the intralobular ducts. Parasympathetic nerve stimulation (2, 5 or 10 sec(-1)) elicited different responses in each of the two microcirculations. Flow in the capillaries around the acini slowed initially before increasing. In contrast, flow in the intralobular duct capillaries increased soon after beginning stimulation.3. In some experiments both whole gland flow and microvascular flow were monitored simultaneously. Whole gland flow increased at the same time as flow in the acinar capillaries was decreasing and as flow in the intralobular duct capillaries increased. Flow in acinar capillaries increased about 5 sec after glandular flow started to increase.4. These observations could be explained if either the vascular beds of the acini and the intralobular ducts were arranged in parallel or if arteriovenous anastomoses were to shunt the acinar circulation. No such anastomoses were found in latex casts made of the gland vasculature, and microspheres injected into the artery supplying the gland were not found in the venous effluent.5. The intraglandular distribution of microspheres was measured in histological sections of the injected glands to give an estimate of the distribution of blood flow between the duct and acinar microcirculations. At rest and during maintained stimulation about 55% of the blood flow passed through the intralobular duct microcirculations, whilst during this initial 15 sec of stimulation this proportion was increased to over 70%. This finding is consistent with a parallel arrangement of the two microcirculations.6. The conclusions drawn from these observations are that the duct and acinar microcirculations are arranged in parallel, that there are differences in the way the vasodilatation is mediated in these circulations, and that arterio-venous anastomoses play no significant role in this gland.

The ultrastructure of the sheep parotid gland

The sheep parotid is a compound tubular gland; its ultrastructure reflects the function of this gland to secrete large amounts of fluid with very little protein. The cells of the secretory tubules possess extensively folded lateral plasma membranes and a fairly large number of mitochondria. Rapid equilibration of water across the epithelium is assured by the close proximity over large areas of intercellular spaces and the wide secretion canaliculi. Numerous long microvilli extend into the latter. Although secretion granules may be quite numerous, there is evidence that many of these granules are not discharged but undergo degradation by lysosomal enzymes. The intercalated ducts are often dilated but excessive distension is probably prevented by bundles of microfilaments in their epithelial cells.

Mineralocorticoid receptors in sheep kidney and parotid: studies in Na+ replete and Na+ deplete states

1. As an adrenalectomized sheep becomes progressively more Na+ deplete, its salivary electrolyte secretion becomes increasingly sensitive to exogenous aldosterone administration. 2. Alteration in mineralocorticoid receptor affinity or concentration is a possible mechanism whereby this sensitivity could be expressed at a molecular level. 3. Bonding sites with a high affinity for aldosterone (Kd 37 degrees C approximately 5 x 10(-10) M) have been demonstrated in sheep kidney and parotid. 4. Renal binding sites were examined in detail, and shown to have affinity characteristics appropriate for mineralocorticoid receptors (aldosterone greater than deoxycorticosterone greater than dexamethasone greater than cortisol greater than progesterone greater than oestradiol greater than dihydrotestosterone). 5. No difference in mineralocoticoid receptor affinity or concentration could be shown between Na+ replete and Na+ deplete sheep, in either kidney or parotid gland. 6. Accordingly, the molecular mechanisms whereby parotid sensitivity is mediated remain as yet undefined.

Proceedings: Osmoreception and thirst in the dog

Images

Membrane potential measurement in parotid acinar cells

1. Intracellular recording of membrane potential was made from acinar cells of the isolated mouse parotid gland superfused with physiological salt solutions.2. The mean acinar resting membrane potential was - 68.5 mV during superfusion with Krebs-Henseleit solution. Shift of the superfusion solution to one containing ACh or adrenaline (10(-5)M) always caused a transient hyperpolarization (about 10-15 mV).3. The membrane potential was mainly dependent on the extracellular K concentration ([K](o)). Increasing [K](o) tenfold decreased the membrane potential by 50 mV. This depolarization was not mediated by ACh release from depolarized nerve endings, since it was seen in the presence of atropine (1.4 x 10(-6)M) and not caused by the accompanying reduction in [Na](o) to 40 mM caused only a small depolarization (less than 10 mV).4. When the superfusion solution was shifted, during intracellular recording, from a normal Krebs-Henseleit solution ([K] = 4.7 mM) to a K-free solution, a hyperpolarization of about 8 mV was measured. Reintroduction of the normal K-containing solution after a longer period of K deprivation (30-70 min) resulted in a short-lasting pronounced hyperpolarization (about 20 mV) which could be blocked by Strophanthin-G (10(-3)M).5. In contrast to previous reports, the present findings indicate that the membrane potential of salivary acinar cells is similar, with respect to magnitude and K-dependence, to that of cells of more thoroughly investigated tissues, such as muscle and nerve, and that the membrane Na-K pump is electrogenic, at least when the cells have been loaded with Na.

Transport of calcium in the perfused submandibular gland of the cat

1. In the perfused cat submandibular gland efflux and influx of (45)Ca, and concentrations of K, (40)Ca and Mg in the effluent from the gland were measured under different experimental conditions.2. When the standard perfusion fluid was shifted to a high Mg (5 mM) or a low Ca (0.25 mM) solution the efflux of (45)Ca from the pre-labelled gland declined. The magnitude and the duration of the effect of the high Mg concentration was more marked at a low external Ca concentration and was abolished by Mersalyl (1 mM). When the standard perfusion fluid was shifted to a Mg-free solution the efflux of (45)Ca from the pre-labelled gland increased.3. After shift of (45)Ca containing perfusion fluid from normal to a high Mg (5 mM) solution the influx of (45)Ca to the gland increased rapidly.4. Both acetylcholine (ACh) and adrenaline caused a marked increase in the efflux of (45)Ca from the pre-labelled gland. This increase in efflux was also seen under conditions where the gland was unable to secrete, i.e. during perfusion with Ca-free and Na-free tetraethylammonium Locke solutions.5. Stimulation with ACh failed to reveal any rapidly occurring increase in influx of (45)Ca.6. Stimulation with ACh evoked a small temporary increase in the concentration of (40)Ca. and Mg in the effluent.7. It is suggested that Ca uptake by intracellular Ca-accumulating systems of the submandibular gland depends on the external Mg concentration and that ACh and adrenaline cause a release of Ca bound intracellularly.

Formation of saliva and potassium transport in the perfused cat submandibular gland

1. In the cat submandibular gland perfused with modified Locke solutions, salivary secretion during acetylcholine (ACh) infusion and K uptake from the perfusion fluid after the ACh-induced K loss were measured.2. Strophanthin G (10(-5)M) abolished K uptake, whereas salivary secretion was unaffected.3. Ethacrynic acid (10(-4)-2 x 10(-4)M) hardly affected K uptake whereas salivary secretion was severely inhibited.4. During perfusion with Ca-free solution K uptake was unaffected, whereas salivary secretion was severely reduced.5. The presence or absence of CO(2)/HCO(3) in the perfusion fluid was of no importance for the secretory process and the K uptake. Acetazolamide (2 x 10(-4)-10(-3)M) did not inhibit these transport processes.6. It is suggested that two kinds of Na transport occur in the acinar cells of the salivary glands: a Na extrusion coupled with K uptake, responsible for the maintenance of the concentration gradients across the cell membrane; and a Na transport coupled with Cl transport into the acinar lumen, responsible for the formation of the primary secretion.