Biomedical subjects

J R Garrett

Publications and source records attributed to J R Garrett.

At least 91 records · Page 5Linked to original sources

PubMed1989

Effects of secretory nerve stimulation on the movement of rat parotid amylase into the circulation.

Stimulation of the nerves to the rat parotid gland demonstrated that increases in serum amylase levels can originate exclusively from this gland. However, whilst parasympathetic nerve stimulation caused a significant movement of parotid amylase into the blood, sympathetic nerve stimulation did not, despite the higher concentration of amylase in the saliva evoked. Experiments in which conscious animals were fed for a short period showed that parotid amylase reaches the blood during normal activity. The mechanisms underlying the movement of parotid amylase into the circulation are still unknown but there appears to be some dependence on the volume of saliva being produced.

Amylases↗

PubMed1989

Depletion of large dense-cored vesicles from parasympathetic nerve terminals in rat parotid glands after prolonged stimulation of the auriculotemporal nerve.

Large dense-cored vesicles (60-100 nm in diameter) have been assessed electron-microscopically in terminal parasympathetic axons at acinar neuro-effector sites in rat parotid glands. Their numbers in control unstimulated glands have been compared with those in the contralateral glands of the same animals after prolonged nerve stimulation. Bilateral postganglionic sympathectomy had been undertaken 4-6 weeks previously to remove adrenergic axons from the glands. Stimulation of the postganglionic parasympathetic nerve to the gland--the auriculotemporal nerve--for 80 min at 40 Hz caused a significant depletion of large dense-cored vesicles from the terminal axons. This depletion corresponded in time and magnitude to the depletion of vasoactive intestinal peptide and substance P from the glands that had been found previously to occur under identical conditions. This adds support to the belief that the neuropeptides are stored in such vesicles and that these vesicles release their contents at neuro-effector sites as a result of propagated impulse formation in the axons.

Animals↗

PubMed1989

Differences in the protein composition of rat parotid salivas evoked by sympathetic and parasympathetic nerve stimulation.

1. Parotid salivas were collected from rats following electrical stimulation of either the sympathetic or parasympathetic nervous supplies. 2. The protein compositions of these salivas were compared using high performance ion-exchange chromatography (FPLC), SDS electrophoresis and biochemical assay. 3. Chromatography and electrophoresis indicated differences between the protein compositions of sympathetic and parasympathetic salivas. 4. Protein secretion derived solely from the exocytosis of parotid acinar cells cannot account for these differences.

Animals↗

PubMed1989

Protein secretion from the cat parotid gland on nerve stimulation.

1. The output and composition of proteins in nerve stimulated saliva samples were compared. 2. Protein output upon parasympathetic stimulation was higher than following sympathetic stimulation and was accompanied by an obvious degranulation of acini with the former but not the latter. These events are the converse of those in the rat parotid gland. 3. Superimposition of sympathetic upon parasympathetic stimulation caused an augmented output of salivary protein. 4. Electrophoresis of salivas revealed differences between individual cats in protein composition but not between differently stimulated salivas.

Animals↗

PubMed1989

Enzyme histochemical discrimination between tryptase and chymase in mast cells of human gut.

We tested four synthetic substances for their histochemical value to demonstrate the catalytic activities of chymase or tryptase in mast cells in sections of human gut. Both Suc-Ala-Ala-Phe-4 methoxy-2-naphthylamide (MNA) and N-acetyl-L-methionine-alpha-naphthyl ester (alpha-N-O-Met) reacted with chymase but not tryptase in mast cells. Conversely, D-Val-Leu-Arg-MNA and Z-Ala-Ala-Lys-MNA were hydrolyzed by mast cell tryptase but not chymase. These results were confirmed by use of two inhibitors of chymotrypsin-like activity, chymostatin and Z-Gly-Leu-Phe-chloromethyl ketone (CK) and two inhibitors of trypsin-like activity, Tos-Lys-CK and D-Val-Leu-Arg-CK. Excellent staining reactions were obtained on cryostat sections of unfixed or aldehyde-fixed tissues and on paraffin sections of Carnoy-fixed tissues. For chymase, however, Suc-Ala-Ala-Phe-MNA is preferred on cryostat sections because it is more specific. On paraffin sections alpha-N-O-Met is preferred because other cells are not then stained. For tryptase, Z-Ala-Ala-Lys-MNA was more selective and more specific and is the preferred general purpose substrate on cryostat sections of aldehyde-fixed tissues and for paraffin sections. D-Val-Leu-Arg-MNA is the preferred substrate for cryostat sections of unfixed tissue. Only a limited number of mast cells showed a reaction for chymase, and these occurred mainly in the submucosa. All mast cells, however, gave a reaction for tryptase, and we recommend the use of either substrate for this enzyme for routine detection of mast cells in human tissues. Double staining for the two main mast cell proteases is most conveniently undertaken on paraffin sections of Carnoy-fixed tissues using MNA substrates for tryptase and alpha-N-O-Met for chymase.

2-Naphthylamine↗

PubMed1989

Effects of streptozocin-induced diabetes on sympathetic and parasympathetic stimulation of parotid salivary gland function in rats.

Diabetes was induced with streptozocin in male Wistar rats. After 4-6 mo, parotid salivary flow was induced by stimulating bipolar electrodes (3-5 V for 2 ms) on either the auriculotemporal nerve (5 Hz) or the cervical sympathetic trunk (10 Hz). During parasympathetic stimulation, flow rates were 443 +/- 287 microliters/30 min in diabetic animals compared to 657 +/- 134 microliters/30 min in controls (P less than .01). Although parotid flow rates during parasympathetic stimulation were well maintained in controls, they decreased rapidly in most diabetic rats. Parotid secretory response to sympathetic stimulation was also reduced in diabetic compared with control animals (40 +/- 16 microliters/30 min and 82 +/- 50 microliters/30 min, respectively, P less than .01). In contrast to results obtained with direct neural stimulation, no differences in threshold dose or total saliva were observed when cholinergic (methacholine) and peptidergic (physalaemin) agonists were administered intravenously. Response threshold for an adrenergic agonist (epinephrine) was significantly increased in diabetes. Electron microscopy showed axoplasmic abnormalities in nonmyelinated axons in diabetic glands but not in control glands. Although most nerve profiles appeared normal, neuroaxonal abnormalities were found in every diabetic animal. The ultrastructural findings and the similar responses to methacholine and physalaemin suggest that autonomic neuropathy may be a factor in the abnormal response of the parotid gland to parasympathetic nerve stimulation.

Amylases↗

PubMed1988

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.

Animals↗

PubMed1988

Morphological changes in the rabbit submandibular gland after parasympathetic or sympathetic denervation.

Selective denervation was used to obtain further information about the relative roles of the nerves supplying the gland. Parasympathetic denervation soon caused atrophy in both acinar and granular tubule cells, and a substantial reduction in gland wet weight. The secretory cells had several unusual features, and striated duct cells tended to accumulate glycogen. Three to four weeks after pre-ganglionic parasympathectomy, the parenchymal cells were less abnormal but still smaller than in the control, unoperated gland. Thus, parasympathetic impulses are required to maintain normal parenchymal cells. Chronic sympathectomy caused little or no detectable changes in the secretory cells, and there was no significant change in wet weight. Nevertheless, pre-ganglionic sympathetic axotomy reduced the reflex secretion of acinar mucosubstances in response to feeding. Thus, sympathetic impulses normally contribute to the reflex secretion of acinar mucosubstance from these glands.

Animals↗

PubMed1988

Influences of short-term sympathectomy on the composition of proteins in rat parotid saliva.

The protein constituents in parasympathetically evoked saliva from normal and short-term sympathectomized parotid glands were compared. There was a reduction in all proline-rich proteins (PRP) in the saliva following sympathectomy. The decrease was quantified for acidic PRP by high-performance ion-exchange chromatography, which showed an increase in the ratio of amylase to other proteins. These results suggest that sympathetic impulses influence the synthesis of PRP and amylase in opposite directions.

Amylases↗

PubMed1988

"Paralytic' secretion after parasympathectomy of rabbit submandibular glands includes a cholinergic component.

Chronic parasympathetic decentralization of submandibular glands in rabbits has been studied after 3 weeks, in acute experiments under urethane anaesthesia. A "paralytic' secretion occurred from the supersensitive denervated glands and it was not attributable to an increase in the "spontaneous' flow, that is present in normal glands. The "paralytic' secretion was completely inhibited by atropine, after which a "spontaneous' flow, that was similar to the contralateral glands, persisted. The alpha-adrenergic blocker dihydroergotamine, when given before atropine, reduced the "paralytic' secretion by 50-75% but when this drug was given after atropine it had no additional effect. The beta-adrenergic blocker propanolol did not cause a reduction in the "paralytic' secretion. Superior cervical ganglionectomy, in contrast, did not give rise to a significant "paralytic' flow. The results suggest that acetylcholine, released spontaneously from terminals of postganglionic parasympathetic nerves, plays an essential part in the "paralytic' secretion that occurs from rabbit submandibular glands after preganglionic denervation. Circulating catecholamines make a secondary contribution, acting synergistically with the acetylcholine on the supersensitive secretory cells.

Animals↗

PubMed1988

Advantages of burst stimulation for inducing sympathetic salivary secretion in rats.

Electrical stimulation of the cervical sympathetic nerve trunk delivered at 50 Hz in bursts of 1 s every 10 s, evoked a more copious, uniform and reproducible flow of saliva than when delivered at 10 Hz continuously. This advantage of burst stimulation occurred with parotid secretion and was especially evident with secretion from submandibular glands, where the oedema, commonly seen after stimulating the sympathetic nerve continuously, was avoided. Therefore stimulation in bursts is recommended for obtaining sympathetic salivary responses in rats.

Animals↗

PubMed1988

Submandibular responses to stimulation of the sympathetic innervation following parasympathetic denervation in cats.

1. The effects of continuous stimulation of the ascending cervical sympathetic nerve were compared with those of intermittent stimulation in bursts, so arranged as to deliver the same total number of impulses, in cats under chloralose anaesthesia 3 weeks after excision of the chorda tympani. 2. Parasympathetic denervation of the gland in this way enhanced the vasodilator component of the vascular response during sympathetic stimulation in bursts. During continuous stimulation this was manifested as a reduced rise in submandibular vascular resistance (SVR). It also produced a profound increase in the secretory response to sympathetic stimulation at low intensity (2 Hz continuously). 3. Enhancement of the salivary secretory responses by stimulating intermittently at relatively high frequencies resembled that which developed following parasympathetic denervation in that there was no change in the secretory capacity during maximal or supramaximal stimulation. 4. Pre-treatment with atropine substantially reduced the flow of saliva in response to sympathetic stimulation at low frequencies (2 and 5 Hz continuously) and combined pre-treatment with atropine and propranolol effectively reversed the increase in secretory sensitivity due to parasympathetic denervation indicating that beta-adrenergic and muscarinic responses are involved. Additional pre-treatment with dihydroergotamine effectively abolished the secretory response to sympathetic stimulation. 5. Stimulation in bursts was found to have a significantly greater vasodilator effect than continuous stimulation at the corresponding frequency after parasympathetic denervation. 6. Neither pre-treatment with atropine nor combined pre-treatment with atropine and propranolol had any significant effect on the changes in mean SVR at any frequency tested during or after either pattern of stimulation. Additional pretreatment with dihydroergotamine effectively abolished the vascular responses to sympathetic stimulation both continuous (5 Hz) and in bursts (50 Hz), leaving a small vasoconstrictor response that may be due to release of neuropeptide Y (NPY). 7. These results suggest that cholinergic beta-adrenergic and NPY supersensitivities are not involved in the submandibular vascular changes that result from parasympathetic denervation, but that alpha-mediated secondary vasodilator mechanisms are thereby enhanced.

Animals↗

PubMed1988

The effects of atropine and chronic sympathectomy on maximal parasympathetic stimulation of parotid saliva in rats.

1. The effects of stimulating the postganglionic parasympathetic nerve to the parotid gland, the auriculo-temporal nerve, continuously at 40 Hz for 80 min have been assessed on the flow of saliva and its amylase content during each 10 min period and on the glandular morphology at the end of the stimulation, in female Sprague-Dawley rats under chloralose anaesthesia. Adrenergic responses were blocked by prior administration of dihydroergotamine (1 mg/kg I.P.) and propranolol (1 mg/kg I.P.). The contralateral unstimulated parotid gland from each animal was used for morphological control purposes. 2. In normal animals there was a copious flow of saliva reaching 3 ml or more in 80 min. It was well maintained after a gradual small decline and the flow in the last 10 min period was still 60% of that in the initial period. Amylase output was relatively high in the initial period but then declined more rapidly than the flow. The acini were densely packed with granules on the control side and showed a moderate amount of degranulation on the parasympathetically stimulated side. 3. After atropine (2 mg/kg I.V.), normal animals initially showed a moderate flow of saliva, being 41% of the non-atropinized animals, but there was a rapid decline and the total flow over 80 min was only 15% of that in the non-atropinized animals. The amylase secreted was also high initially and showed a rapid decline; the total amount secreted was similar to that in non-atropinized animals. The morphology was similar to that in non-atropinized animals and showed a similar loss of acinar granules on the stimulated side. 4. Chronic bilateral postganglionic sympathectomy (4-6 weeks duration) caused a drastic reduction in the capacity of the gland to secrete saliva in response to parasympathetic stimulation, reaching only one-third of that from normal animals. The initial output of amylase was greater than in normal animals but the total output was similar. The control unstimulated sympathectomized glands appeared similar morphologically to normal resting glands. However, on the parasympathetically stimulated side, besides the usual amount of acinar degranulation, there was also a conspicuous development of acinar vacuolation, not seen in the other groups of animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Amylases↗

PubMed1988

Immunohistochemical localization of Na+,K+-ATPase in rodent and human salivary and lacrimal glands.

The enzyme Na+,K+-ATPase was localized immunohistochemically in major salivary glands of mouse, rat, and human and in exorbital lacrimal glands of the rodents. Immunoreactive Na+,K+-ATPase was abundant in the basolateral membranes of all epithelial cells lining striated and intra- and interlobular ducts of all glands. Reactivity of intercalated ducts varied among gland type and species. Cells lining granular ducts in rodent submandibular gland showed a heterogeneous staining pattern in rat but stained homogeneously in mouse. Secretory cells varied greatly in their content of immunoreactive Na+,K+-ATPase. As with all duct cells, staining was present only at the basolateral surface and was never observed at the luminal surface of reactive secretory cells. Mucous cells failed to show any reactivity in any gland examined. Serous cells showed a gradient of immunostaining intensity ranging from strongly positive in demilunes of human sublingual gland to negative in rat submandibular gland and lacrimal glands of rats and mice. The presence of basolaterally localized Na+,K+-ATPase in most serous cells but not in mucous cells suggests that the enzyme contributes to the ion and water content of copious, low-protein serous secretions. The intense immunostaining of cells in most if not all segments of the duct system supports the idea that the ducts are involved with modification of the primary saliva, and extends this concept to include all segments of the duct system.

Animals↗

PubMed1987

Electron microscopy of watery vacuole formation in rat parotid acinar cells during reflex stimulation.

Reflex stimulation from eating hard chow caused variable degrees of watery vacuolation, most conspicuously in animals that had eaten the most food; this was accentuated by eating in the cold. Some vacuolation occurred in the absence of sympathetic impulses but there was much more in glands receiving both parasympathetic and sympathetic impulses. Vacuole formation was often associated with, but not dependent upon, a degree of acinar degranulation. The vacuoles appeared to originate either from the inner side of the Golgi apparatus, near condensing vacuoles, or from ballooning within the rough endoplasmic reticulum; some vacuoles appeared to arise close to secretory granules. Certain cellular components, including secretory granules, entered the contents of vacuoles, which also often had connections with lumina. Many basally-located vacuoles were large and bounded only by a tenuous layer of cytoplasm which was contained by the basal lamina. Vacuole formation may be related to strong stimulation of susceptible cells, which occurs to a variable extent during natural reflex secretion, as well as during artificial stimulation. Thus, under normal conditions, certain macromolecular components might enter saliva via this route and not solely by exocytosis. Leakages from acinar vacuoles could also occur into the glandular interstices, accounting for some of the parotid amylase found in peripheral blood.

Animals↗

PubMed1987

Factors affecting the secretion of submandibular salivary kallikrein in cats.

Glandular kallikrein has been assessed in submandibular saliva, homogenates and plasma by the fluorimetric substrate D-Val-Leu-Arg-7-amino-4-trifluoromethylcoumarin (AFC) and histochemically in tissue sections by the 4-methoxy-2-naphthylamide (MNA) analogue. Nerve stimulation was used to produce salivary secretion. Parasympathetic saliva contained low concentrations of kallikrein, independently of any circulating catecholamines from the adrenals. Sympathetic saliva contained very high concentrations of kallikrein; the amounts in individual drops rapidly reached a peak then declined gradually. Adrenergic blocking drugs during mixed parasympathetic and sympathetic stimulation showed that beta-adrenergic effects normally increase the secretion of kallikrein in response to the alpha-adrenergic influence from sympathetic nerve impulses. Small amounts of a glandular kallikrein-like activity are present in the plasma. Effluent blood from the submandibular gland before, during and after stimulation of either nerve gave no indication that submandibular kallikrein passes from the glandular compartment to the blood under conditions of unobstructed salivary flow. Excision of the chorda tympani indicated that parasympathetic nerve impulses are required for the normal resynthesis of submandibular kallikrein. The secretion of salivary kallikrein is essentially an exocrine function but its role in the saliva remains obscure. The results suggest that sudden mobilization of kallikrein may occur at times into the saliva and that a separate population of adrenergic axons, under separate central control, may pass to the striated ducts specially for this purpose.

Animals↗

PubMed1987

Effects of stimulating the sympathetic innervation in bursts on submandibular vascular and secretory function in cats.

1. The effects of continuous stimulation of the peripheral end of the ascending cervical sympathetic nerve were compared with those of intermittent stimulation, so arranged as to deliver the same total number of impulses, in cats under chloralose anaesthesia. 2. Continuous stimulation caused a flow of saliva at 5-10 Hz, but not at 2 Hz. In contrast, the same total number of impulses delivered intermittently in bursts elicited a prompt secretion at a frequency as low as 20 Hz for 1 s at 10 s intervals (corresponding to 2 Hz continuously) and a significantly higher rate of secretion at 50 Hz in bursts than that obtained in response to 5 Hz continuously. 3. Continuous stimulation also caused a rise in submandibular vascular resistance (s.v.r.), which persisted throughout the period of stimulation, and was followed immediately thereafter by an intense but transient fall in s.v.r. During stimulation in 1 s bursts, each burst was followed first by a brief rise in s.v.r. and shortly after by a fall. The balance between these two components varied widely between individual animals but often led to an overall fall in s.v.r. during stimulation i.e. complete reversal of the mean vascular effect. A further fall in s.v.r. was then recorded when the stimulus was discontinued. 4. Propranolol (1.0 mg/kg) reduced but failed to abolish the secretory response. It also altered the balance between the two phases of the vascular response slightly in favour of a rise in s.v.r. during stimulation, without apparently affecting the size of the after-dilatation. 5. Pre-treatment with dihydroergotamine (1.0 mg/kg) invariably blocked secretion and revealed a small vasodilator response during sympathetic stimulation with either pattern of stimulation; it also blocked the after-dilatation. 6. Following combined pre-treatment with propranolol and dihydroergotamine, to produce total adrenergic blockade, there was a small residual vasoconstrictor component which amounted to an increase in mean s.v.r. of about 20% during stimulation at 10 Hz continuously. This may have been due to release of neuropeptide Y (NPY). 7. Small but significantly greater amounts of NPY were released into the effluent blood during stimulation of the ascending cervical sympathetic nerve at 70 Hz in bursts than during continuous stimulation. No significant release of vasoactive intestinal peptide (VIP), somatostatin, bombesin, substance P or calcitonin gene-related peptide (CGRP) was observed during stimulation at any frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

The proper role of nerves in salivary secretion: a review.

Consideration of the history of this subject has created a perspective which helps one to appreciate how errors in thinking have occurred and why some have persisted, despite subsequent improvements in information. The most enduring misconception has been that the drying of the mouth under stress is due to sympathetic inhibitory fibers, a view that must be eradicated, for such fibers do not exist. The inhibition is due to central influences from higher centers acting on the salivary centers and thereby suppressing reflex activity. Wide variations exist in the neuro-effector arrangements and in the cellular responses in different glands from different species. Myoepithelial cells are usually contracted by both parasympathetic and sympathetic nerves. The blood vessels also receive a dual innervation, but parasympathetic impulses cause vasodilatation as part of secretion, whereas the sympathetic vasoconstrictor fibers are part of a more generalized vascular control system and not a direct part of the reflex secretory sympathetic pathway. Parasympathetic drive usually provides the main stimulus for fluid formation by parenchymal cells, whereas sympathetic nerves tend to increase the output of pre-formed components from certain cells. Absence of nerve impulses causes variable atrophic and other metabolic effects on the parenchymal cells. Evidence is beginning to accrue that certain nerve impulses may influence resynthetic activities. Vacuolation, often found experimentally after strong stimulation, also occurs to a variable extent in certain cells as a normal part of reflex secretion and may therefore have an effect on the components entering the saliva. If rupture of vacuoles occurs, then this may contribute to the salivary amylase that is present in the blood. Recent evidence points to the possibility that, even in a monomorphic gland, not all of the components necessarily enter nerve-induced saliva in "parallel" proportions. Consideration of current information has enabled some provisional generalizations about the roles of the secretory nerves to be suggested in the summary, but they must not be considered immutable.

Animals↗