Interaction between sympathetic and parasympathetic salivary nerves in anaesthetized dogs

Nizatidine enhances salivary secretion in patients with dry mouth

OBJECTIVE

It was reported that salivary secretion increased in 30 volunteers with administered nizatidine. The aim of the present study was to investigate whether or not nizatidine enhances salivary secretion and improves the function of salivary glands in patients with dry mouth.

METHODS

Both basal and stimulated salivary secretions were measured before and after the administration of nizatidine for a month in 18 healthy adult volunteers and 38 patients with dry mouth. In 6/38 patients, salivary gland scintigraphy was performed.

RESULTS

After the administration of nizatidine for a month, salivary secretions significantly increased in the control and dry mouth patient groups compared to the pretreatment baseline. In addition, 25 of 38 dry mouth patients showed subjective improvements of oral dryness. In 3/4 patients, the function of salivary glands was improved on salivary gland scintigraphy.

CONCLUSION

Nizatidine may reactivate salivary gland cells and be useful in the treatment of patients with dry month.

Oral dryness and peripheral neuropathy in subjects with type 2 diabetes

Two common complaints related to diabetes mellitus are oral dryness (xerostomia) and peripheral neuropathy (PN) and there is some evidence of a relationship between them. Therefore, we formulated a hypothesis that type 2 diabetic subjects with xerostomia in our study also exhibited PN. The study included 102 randomly sampled type 2 diabetic patients from a healthcare district in mid-Sweden. Besides clinical and X-ray examinations, patients were asked whether they experienced oral dryness. PN was defined through thorough foot examination and the use of a modified neuropathy symptom score (NSS) and neuropathy disability score (NDS). Other diabetes-related variables were extracted from medical records. More than half of the individuals (53.5%) reported oral dryness and 23.8% were diagnosed with PN. None of the variables in a stepwise regression analysis could explain the variance in oral dryness, besides "pain in the legs," which contributed with 5% to the explanation. Our hypothesis that type 2 diabetic subjects with xerostomia also were affected with PN could not be verified in this study, but the results must be interpreted with caution as relatively few subjects were affected with both oral dryness and PN (13.8%). Further and larger controlled studies are needed before the hypothesis can be definitely rejected. Despite our incomplete understanding about the relation between oral dryness and PN, professionals in oral health as well as in primary health have to strive for increased knowledge in this field.

Salivary alpha-amylase as a measure of endogenous adrenergic activity

This investigation was designed to evaluate the production rates and concentrations of salivary alpha-amylase as a measure of adrenergic activity under several conditions of stress in human subjects. Saliva and blood samples were simultaneously collected from men at four 15 min intervals both before and after regimens for exercise, a written examination, or a rest period. The regressions of salivary alpha-amylase on plasma norepinephrine (NE) concentrations were significant for both exercise (P < 0.001) and examination (P < 0.01) protocols. Aerobic exercise induced a 3-fold mean increase in alpha-amylase; both NE and epinephrine (EP) increased approximately 5-fold over control levels. Levels of alpha-amylase and NE returned to control levels within 30-45 min after exercise, but EP remained elevated by approximately 2-fold during the remaining hour of observation. During the written examination, alpha-amylase and NE, but not EP, concentrations increased in parallel. In further studies the effects of exercise and exposure to heat and cold on the relationship of salivary alpha-amylase to heart rate and body temperature were investigated. Greater intensities of exercise were associated with greater increases in alpha-amylase concentrations. During heat exposure in a sauna (66 degrees C for 40 min) amylase, heart rate and body temperature all increased progressively. However, during exposure to cold (4 degrees C for 40 min) amylase increased rapidly, though heart rate and body temperature remained unchanged. Salivary cortisol concentrations were unchanged during exposure to heat or cold. We conclude that salivary alpha-amylase concentrations are predictive of plasma catecholamine levels, particularly NE, under a variety of stressful conditions, and may be a more direct and simple end point of catecholamine activity than are changes in heart rate.

Variations in blood flow on mandibular glandular secretion to autonomic nervous stimulations in anaesthetized dogs

1. Continuous stimulation of the preganglionic parasympathetic nerve (the ramus communicans of the mandibular ganglion) for 1-2 min at supramaximal voltage (5 V) and pulse duration (1 ms) increased salivary gland arterial inflow and this was accompanied by copious salivary secretion. The responses were recorded continuously during the period of stimulation. The frequency for initiating the responses was 0.5 Hz. Maximal responses occurred at 16 Hz. The response coefficient of arterial inflow to stimulus frequency was 0.17 ml min-1g-1 Hz-1 and that of secretion to stimulus frequency was 0.016 ml min-1g-1 Hz-1. 2. The secretory response to low and moderate levels of parasympathetic nerve stimulation (below 8 Hz) was not affected by a reduction or cessation in arterial inflow whereas the response to high level parasympathetic nerve stimulation (above 8 Hz) was significantly alleviated if blood flow to the gland was maintained (via controlled vascular perfusion) at a level less than that of the resting arterial inflow. However, when the gland was already secreting near-maximally (stimulated at 8 Hz), sudden cessation of blood flow for a short period of time (0.5-2 min) had no effect on the salivary flow. 3. Continuous stimulation of the cervical sympathetic nerve for 1-2 min at supramaximal voltage (20 V) and pulse duration (1 ms) decreased arterial inflow and this was accompanied by scanty salivary secretion. The vascular response persisted during the period of stimulation. The secretory response was 15 s late in onset and might continue for 1 min after stimulation. The frequency for initiating the responses was 1-4 Hz. Maximal responses occurred at 16-32 Hz. The response coefficient of arterial inflow to stimulus frequency was -0.04 ml min-1g-1Hz-1 and that of salivary secretion to stimulus frequency was 0.001 ml min-1g-1Hz-1. 4. The secretory response to sympathetic nerve stimulation at different frequencies in glands with blood flow maintained at resting rate (via controlled vascular perfusion) resembled that in glands with spontaneous blood flow. 5. Sympathetic nerve stimulation was found to retard salivary secretion caused by parasympathetic stimulation, irrespective of whether the gland received spontaneous arterial inflow or controlled vascular perfusion at a resting flow rate. 6. The results suggest that the salivary secretion to stimulation of parasympathetic nerve is independent of blood flow over a wide range of stimulus frequencies; however, the response to high frequency stimulation of the parasympathetic nerve may be affected by fluctuations in blood flow.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibitory effects of atropine and adrenergic antagonists on the changes in autonomic receptors and cyclic nucleotides of rat parotid and submandibular glands caused by sympathetic nerve stimulation

The changes in cyclic AMP (cAMP) concentration and density of beta-adrenoceptors caused by electrical stimulation of the sympathetic innervation to parotid and submandibular glands of rat did not occur when the alpha- and beta-adrenergic antagonists, phentolamine, and propranolol were administered 20 min prior to initiation of stimulation. They also did not occur when phentolamine, the beta-adrenergic antagonist, was administered alone prior to nerve stimulation, indicating that beta-adrenoceptors mediate these effects. Simultaneous administration of the alpha- and beta-antagonists also prevented the changes in densities of muscarinic receptors and cGMP concentrations usually induced by sympathetic nerve stimulation. Also, the changes in muscarinic receptors and cGMP did not occur when atropine was administered prior to nerve stimulation, nor did they occur with simultaneous administration of atropine, phentolamine + propranolol; with phentolamine alone, or propranolol alone, the effects were blocked to a large extent. Secretion was inhibited completely when both adrenergic antagonists were present during nerve stimulation, but flow rate was unchanged when atropine was present. The changes in both beta-adrenoceptors and muscarinic receptors reflect a desensitization caused by prolonged exposure to neurotransmitters released when the sympathetic nerve is stimulated. The changes are prevented when either atropine or adrenergic antagonists are present during nerve stimulation.

Structural and functional studies of the effects of sympathetic nerve stimulation on rabbit submandibular salivary glands

Continuous sympathetic stimulation at 8-10 Hz caused intense vasoconstriction in the gland, so stimulation was generally given in an interrupted pattern to minimize this detrimental effect on secretion. Only a small increase in fluid secretion occurred; it became thick and tended to block the cannula; therefore in later experiments the main duct was not cannulated. After sympathetic stimulation there was substantial degranulation of acinar cells. However, as this was accompanied by little movement of water, the secreted mucosubstance distended the ductal lumina. The granular tubule cells were unchanged by sympathetic stimulation. Use of selective blocking agents revealed that the sympathetically-evoked secretion of acinar mucin was mediated mainly via beta-adrenoreceptor activation. As stimulation of the sympathetic nerves alone caused little additional formation of fluid, the effects of superimposing continuous low frequency sympathetic stimulation onto a background of low parasympathetic secretion were compared with similar parasympathetic stimulation alone of the contralateral gland. These double nerve stimulations did not augment the volume of fluid secreted, or cause morphological changes additional to those from parasympathetic stimulation alone. Nevertheless, it is likely that, under natural reflex conditions, sympathetic impulses can increase the amount of acinar mucosubstance secreted.

Nerve interactions in salivary glands

In the salivary reflex, not only secretory cells are activated, but also myo-epithelial cells are contracted to support these cells and promote the flow of saliva, and blood vessels dilate to meet the increased demands of the tissues. The various effector cells often receive nerves from both parts of the autonomic system, and interactions may occur when the nerves act on the same type of effector, or on different types of effectors. While in an experiment electrical stimulation of the sympathetic trunk may decrease a parasympathetic salivary flow by causing marked vasoconstriction, this does not occur in the salivary reflex, since the vasoconstrictors do not take part. On the contrary, the normal sympathetic vasoconstrictor tone of the resting gland is easily overcome by activity in parasympathetic vasodilator nerves when secretion starts. Pronounced synergism can be demonstrated between sympathetic and parasympathetic secretory nerves. In dogs, for instance, in which sympathetic secretion is beta-adrenoceptor-mediated, this is marked in the case of fluid secretion. In rats and rabbits, in which beta-receptors elicit secretion of amylase, the potentiating interaction among the nerves is striking when amylase secretion is considered. Even the random release of acetylcholine from the post-ganglionic parasympathetic axons, by itself insufficient to evoke secretion, can increase the sympathetic effects. Motor nerves interact with secretory nerves by causing myo-epithelial contraction, mechanically promoting secretion. Interactions between the nerves in their long-term regulatory function on the sensitivity of the acinar secretory and myo-epithelial cells can also be demonstrated.

Autonomic correlates of alimentary conditioned and unconditioned reactions in the dog

Analysis of changes in cardiac action and the secretion of saliva during unconditioned alimentary activity in 6 dogs revealed that the beginning of food consumption was accompanied by acceleration of the heart rate (HR) without an increase in salivation. In the course of eating, the heart rate decelerated and salivation increased. Alimentary conditioned stimuli of excitatory (CS+) and inhibitory (CS-) character always produced cardiac acceleration, which in the case of CS+ was accompanied by secretion of saliva. The findings indicate that during food consumption activation of the autonomic system depends upon the contents of motivational processes. In the course of an alimentary act the parasympathetic withdrawal (heart rate acceleration and decrease in salivation) seems to reflect the drive component of the act, while the following parasympathetic activation (heart rate deceleration and increase in salivation) is probably associated with an hedonic component of the consummatory reaction. In our study alimentary conditioned stimuli evoked both drive and hedonic components of alimentary motivation.

Sympathetic stimulation of amylase secretion during a parasympathetic background activity in the rat parotid gland

The amylase secretion in vivo was examined in the rat parotid gland. A comparison was made between individual stimulation of sympathetic and parasympathetic nerves and simultaneous activation of both nerves. When sympathetic stimulation was superimposed on a parasympathetic background activity, amylase secretion was elicited at a frequency far below the threshold for secretion of fluid, and increased in a frequency-dependent way. This augmented amylase secretion, seen when the two nerves were activated at the same time, gave an amylase output which far exceeded the sum obtained at individual nerve stimulation. The sympathetic amylase secretion obtained in a background of parasympathetic activity seemed to be dependent entirely on beta 1-adrenoceptors. When high sympathetic stimulation frequency (3-10 Hz) was used a reduction in salivary flow was seen, which was accompanied by a reduced amylase output. This effect was counteracted by alpha-adrenoceptor blockade. Isoprenaline, injected intravenously during an ongoing parasympathetic activity, was found to evoke an augmented amylase secretion in a similar way as sympathetic nerve stimulation.

Isoprenaline-induced facilitation of the Eustachian tube opening

Isoprenaline was given i.v. to rats and its ability to change the air pressure necessary to open the Eustachian tube (ET) was studied. Air was injected once a minute into the middle ear via a tube glued to a hole in the tympanic bulla. The rate of pressure increase was 0.7 kPa/sec. The air pressure at which the ET opened was in 10 rats 3.4 +/- 0.3 (SE) kPa. Isoprenaline in a dose of 1 microgram/kg decreased this pressure opening level (Pol) by 0.14 +/- 0.03 kPa and with 10 micrograms/kg by 0.22 +/- 0.03 kPa. These effects were reduced by propranolol. Isoprenaline did not act via released adrenaline. A surface tension lowering substance, Tween 20, instilled into the middle ear, decreased Pol by about 0.9 kPa. It is suggested that isoprenaline evokes a decreased Pol via secretion of surface tension lowering substances.

Adrenergic nerves to the rat parotid gland originating in the contralateral sympathetic chain

The parotid gland of the rat seems to receive some adrenergic nerves from the sympathetic chain of the opposite side. This is suggested by the following evidence: after unilateral removal of the superior cervical ganglion, parotid tissue from the contralateral gland shows degeneration secretion of amylase in vitro similar to, but much smaller than that known to occur ipsilaterally. When parotid secretion is evoked parasympathetically in the anesthetized rat, superimposed stimulation of the contralateral cervical sympathetic trunk can be shown to increase the secretion of amylase into this parasympathetic saliva; as it does, much more, ipsilaterally. It may also cause an evanescent decrease of the salivary flow, suggesting that not only secretory, but also vasoconstrictor nerves had been activated. After removal of one sympathetic ganglion, some undergenerated adrenergic nerves remain ipsilaterally, as earlier demonstrated; but no such fibers can be detected when the ganglion has been removed on both sides.

Effects of some alpha-adrenoceptor stimulating and blocking agents on the salivary amylase secretion in the rabbit

In rabbits under urethane anaesthesia parotid secretion of fluid and amylase in response to electrical stimulation of the sympathetic and parasympathetic nerves was measured before and after injections of various agents acting on alpha-adrenoceptors. Amylase secretion in response to sympathetic nerve stimulation at 0.5 and 1 Hz was markedly reduced by clonidine, 0.5-30 micrograms/kg, in a dose related manner. The effect was not due to an altered responsiveness of the gland, since isoprenaline still caused a large release of amylase. Phenylephrine, 10 micrograms/kg, and prazosine, 300 micrograms/kg, had no effect on the sympathetically evoked amylase secretion. Yohimbine in a dose of 0.5 mg/kg increased the amylase output in response to sympathetic nerve stimulation at 0.5 Hz by 70%, while the response at 1 Hz, which is close to maximum for the gland, was not significantly increased. The fluid and amylase secretion produced by parasympathetic nerve stimulation at 1.5, 5.0 and 10 Hz remained unchanged after clonidine, 1.0-30 micrograms/kg, or yohimbine 0.5 mg/kg. In rabbits provided with chronic parotid fistulae fluid and amylase secretion were studied after injections of clonidine, 30 micrograms/kg, and yohimbine, 1 mg/kg. In the conscious animal clonidine reduced not only amylase but also fluid secretion, by around 50 and 30%, respectively, indicating an effect on the activity in both the sympathetic and parasympathetic secretory nerves. Yohimbine increased the output of amylase during feeding, seen as an increased mean output of amylase due to an increased concentration of amylase in the saliva, while fluid secretion remained unchanged. The various experiments suggest that amylase secretion in response to sympathetic activation may be influenced by prejunctional control of transmitter release via alpha-2-adrenoceptors, and that this control may be of physiological significance. Parasympathetically evoked secretion does not seem to be under the influence of a similar control.

Blood flow and secretion in the submaxillary gland of the rabbit during stimulation of the autonomic nerves

The excitation of the chorda-tympani nerve caused a marked increase in the blood flow through the gland and in secretion of saliva; both phenomena had a threshold frequency of around 0.3 Hz and reached a maximum at around 20 Hz, where a 6-fold increase in the blood flow and a salivary secretion of at the most 300 microliters/min were seen. Sympathetic excitation severely retarded the blood flow, which almost ceased at frequencies as low as 3-5 Hz; mostly single shocks of sympathetic stimulation reduced the blood flow through the gland. An on-going parasympathetic activation did not alter the effects of sympathetic stimulation on the blood flow and the parasympathetically produced salivary secretion almost stopped. The experiments support previous results, which have suggested electrical excitation of the sympathetic trunk at or above 2 Hz to cause a vasoconstriction which adversely affects the fluid secretion in the rabbit salivary glands.

Complementary role of vasoactive intestinal polypeptide (VIP) and acetylcholine for cat submandibular gland blood flow and secretion

The effects of local intraarterial infusions of VIP, acetylcholine (ACh), substance P, isoprenaline and bradykinin on submandibular gland blood flow and salivary secretion were studied in cats. It was found that VIP (10(-14) to 10(-10) mol/min) caused an atropine resistant vasodilation but no salivary secretion. Several hundred fold higher doses of exogenous VIP had to be infused than the amounts of VIP seen in the venous outflow during maximal nerve stimulation at a similar vasodilatory response. ACh infusions (5 X 10(-12) to 5 X 10(-8) mol/min) caused both a muscarinic vasodilation and salivary secretion. ACh was about 100 times less potent than VIP as a vasodilating agent. Both ACh and VIP induced in high doses a vasodilatory response similar to that seen during parasympathetic nerve stimulation at 15 Hz. ACh by itself did in the present doses, however, only induce about 50-60% of the maximal secretory response. Combined infusions of ACh and VIP, had mostly an additive effect on vasodilation. The salivatory volume response to ACh was potentiated by VIP and to a smaller extent also by isoprenaline. This potentiating effect may be due to a direct effect on secretory elements as well as partly to the additional increase in blood flow. Bradykinin was about 1 000 times less potent than VIP as a vasodilating agent. Substance P (10(-9) mol/min) only caused a weak vasodilation. Since there is evidence that ACh and VIP coexist within the same neurons and are both released upon parasympathetic nervous activation, the present findings suggest that the secretory and vasodilatory responses may be caused by an interaction between these two agents.

Amylase secretion in response to activation of different autonomic receptors in the rabbit parotid gland

The contribution by different autonomic receptors to the amylase secretion from the parotid gland of the anaesthetized rabbit was studied as the response to various parasympathomimetic and sympathomimetic drugs. Amylase secretion by infusions of pilocarpine and parasympathetic nerve stimulation was low, but regularly higher in response to pilocarpine than to parasympathetic nerve stimulation. These effects were reduced to the same level by beta-adrenoceptor block indicating the presence and for pilocarpine also the release of catecholamines, probably from the adrenals. Isoprenaline injections produced a high amylase secretion, that was blocked by atenolol, indicating that predominantly beta 1-adrenoceptors were activated. Phenylephrine was without amylase secretory effects. By accepting isoprenaline maximum as maximum for sympathetically produced amylase secretion, a theoretical frequency-response relationship for amylase secretion by sympathetic nerve stimulation could be calculated: ED50 was 0.9 Hz. The results indicate that under experimental conditions in vivo there are certain differences between the rat and the rabbit parotid glands in the autonomic control not only of fluid, but particularly of amylase secretion.

A morphometric analysis of the autonomic innervation of cat tracheal glands

Quantitative methods have been used to examine the distribution of adrenergic and cholinergic axon varicosities to serous and mucous cells of cat tracheal glands. Cats were injected with 5-hydroxydopamine (5-OHDA) prior to removal of the trachea in order to fill adrenergic vesicles with intensely osmiophilic material. This facilitated the identification of adrenergic varicosities and provided a means by which they could be easily discriminated from cholinergic varicosities. Of all varicosities identified within 10 micrometer of the glands, 90% were cholinergic and 10% were adrenergic. Most of these varicosities were present in interstitial bundles located between acini. A small number of cholinergic varicosities, however, were located within 20 nm of acinar cells, forming close contact junctions. No differential innervation of serous and mucous cells was observed.

Augmented amylase release from rat parotid gland slices, in vitro

Using a continuous amylase assay the effect of a simultaneous stimulation of adrenergic and cholinergic receptors on amylase release by perfused rat parotid slices was investigated. Superimposing adrenergic stimulation (isoprenaline) on continual submaximal cholinergic stimulation (acetyl-beta-methylcholine) resulted in an augmented amylase release compared with the sum of the two separate effects. This could also be shown with continual adrenergic stimulation with cholinergic stimulation superimposed on this. Possible explanations of this effect are discussed with particular respect to the role of Ca++.

Amylase secretion from rat parotid glands as dependent on co-operation between sympathetic and parasympathetic nerves

A slow, long-lasting 'degeneration secretion' from the parotid gland was brought about in anaesthetized rats by section of the auriculo-temporal nerve 16--19 h in advance. This parasympathetic background activity greatly increased the secretion of amylase elicited by sympathetic nerve stimulation.

Effects of sympathetic nerve stimulation in the presence of a slow parasympathetic secretion in the parotid and submaxillary glands of the rabbit

Sympathetic secretory responses from the parotid and the submaxillary glands of the rabbit were studied; sympathetic excitation occurred either alone or during a slow parasympathetic background secretion, imitating the resting secretion normally present. The fairly rapid sympathetically evoked flow of saliva from the parotid gland was, in the background secretion, further increased and obtained at low frequencies, which at sympathetic stimulation alone were subthreshold. The effects, which could be repeated with sympathomimetic drugs in a pilocarpine induced secretion, were abolished by alpha and beta-adrenoceptor blockade in combination. The submaxillary gland gave a very scanty secretion on sympathetic excitation, the effects being mediated via beta-adrenoceptors. The responses were not increased in a background secretion but the main effect of sympathetic activation was to retard the salivary flow. The retardation was attributed to vasoconstriction accompanying sympathetic excitation. Eliminating the vasoconstrictor responses, while retaining the sympathetic secretory effects, did not reveal any increase of the sympathetic salivary responses in the submaxillary gland.