In vivo secretory responses of submandibular glands in streptozotocin-diabetic rats to sympathetic and parasympathetic nerve stimulation

Submandibular gland responses to sympathetic and parasympathetic nerve stimulation were studied in streptozotocin-diabetic rats. Morphologically, the acinar cells in control glands were relatively uniform in size and contained electron-lucent granules. The granular ducts were distinguished by the presence of electron-dense granules. With the exception of intracellular lipid droplets and the presence of a few autophagosomes in diabetic glands, no consistent differences in acinar cell structure were observed. In contrast, the diameter of the granular ducts and the granule content of their cells were less in diabetic glands. At 3 weeks sympathetic flow rate, salivary protein concentration, and total protein output were unaffected by diabetes. Sympathetic flow rate was greater at 3 months, and the concentration of protein in the saliva was lower. In 6-month diabetic rats flow rate remained increased, but protein concentration and total protein output were reduced. The decrease in salivary protein concentration at 3 and 6 months was accompanied by a reduction in secretory granule release from acinar and granular duct cells. No consistent differences in flow rate, protein concentration, protein output, or secretory granule release were observed following parasympathetic stimulation. We conclude that the effects of diabetes on nerve-stimulated flow rate and protein release depend on the duration of diabetes and the type of stimulation, and are independent of one another.     

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.     

Secretory responses in granular ducts and acini of submandibular glands in vivo to parasympathetic or sympathetic nerve stimulation in rats

Summary The roles of sympathetic and parasympathetic nerves in the secretion of saliva from submandibular glands of rats have been tested by electrical stimulation of either nerve for 1 h unilaterally in separate animals. The flows of saliva thereby induced and their protein content were monitored. Structural changes in each gland were assessed by light- and electron microscopy and compared with the unstimulated contralateral control gland, and the extent of the changes was determined morphometrically. Sympathetic nerve stimulation induced a relatively low flow of saliva that was rich in protein and was accompanied by extensive degranulation from both acinar and granular duct cells. In contrast parasympathetic nerve stimulation induced a considerable flow of saliva that had a low protein content and no detectable degranulation occurred from the secretory cells. It is possible, therefore, that some protein in parasympathetic saliva may have arisen from a non-granular pathway.     

Changes in parotid acinar cells accompanying salivary secretion in rats on sympathetic or parasympathetic nerve stimulation

Morphological and secretory effects of stimulating autonomic nerves have been studied in parotid glands of rats. Sympathetic stimulation evoked a slow flow of saliva which had a high concentration of amylase. After long term sympathetic stimulation secretory granules were heavily depleted from the parotid acinar cells. Parasympathetic stimulation evoked a copious flow of saliva with a low concentration of amylase. However, at high frequency stimulation the total amount of amylase secreted on parasympathetic stimulation was as great or even greater than on symphatetic stimulation, nevertheless, any loss of secretory granules from the acinar cells was very small. It is concluded that secretion of parotid acinar granules in the rat is prinicipally a sympathetic function. Secretion of fluid is more effectively produced by parasympathetic stimulation and much of the amylase in such saliva appears to have arisen from sources other than the secretory granules.     

Glycoproteins of submaxillary saliva of the cat: differences in composition produced by sympathetic and parasympathetic nerve stimulation

Abstract— Saliva samples were obtained from the cannulated submaxillary ducts of the cat during stimulation of the peripheral cut end(s) of (1) the cervical sympathetic nerve, (2) the chordalingual (parasympathetic) nerve and (3) both nerves at the same time. In nine experiments the ratios of neuraminic acid to fucose and to hexosamine were consistently 2·5–4 times higher in saliva evoked by sympathetic nerve stimulation than in that produced by parasympathetic stimulation. This was not attributable to differences in the rate of synthesis of the carbohydrate of the glycoproteins or in salivary flow rate. The presence of glycolipids and blood glycoproteins was excluded. Saliva produced by stimulation of the sympathetic and parasympathetic nerves each showed a single, but different, peak after ultracentrifugation in 0·1 m -NaCl with 0·01 m -phosphate buffer (pH 7·4). The S_{20, w} of the former was 6·5 and of the latter, 39. Both peaks were demonstrable in saliva produced when both nerves were stimulated at the same time.     

Responses of the uterine circulation to sympathetic nerve stimulation

Pregnant and non-pregnant sheep uteri were perfused in situ with arterial blood at a constant flow rate. Unilateral stimulation (1-2 ma, u ms pulse) of the distal end of the severed sympathetic chain (L3-L4) at frequencies between 5 and 25 Hz produced a graded increase in uterine artery pressure in both horns. At 25 Hz, pressure in the horn ipsilateral to the stimulated sympathetic chain increased by 28 +/ 2% in four pregnant animals and 32 +/ 5% in six non-pregnant ewes. The response of the contralateral horn was significantly smaller than that of the ipsilateral horn (P less than or equal to 0.05). The response was alpha-mediated since it was abolished by local injection of dibenzyline into the middle uterine artery. The responses of the pregnant and non-pregnant animals were similar, indicating that pregnancy did not alter the alpha-adrenergic responses of the uterine vasculature.     

Selective pharmacological blockade of synaptic transmission in parasympathetic pathways to the heart in rats

The blocking effects of newly synthesized compounds N-decyltropine bromide (IEM-1556) and its derivatives N-methyltropine iodide (IEM-1893) and N-hexyltropine iodide (IEM-1848), possessing aliphatic radicals of different length, on the vagus-induced reduction of the heart rate were studied in acute experiments on rats. The effects produced by these compounds on the level of arterial blood pressure and synaptic transmission in the superior cervical ganglion (SCG) of the rat were studied and compared with those produced by classical ganglion-blocking agents (hexamethonium and trimetaphan) and muscle relaxants (pancuronium and decamethonium). IEM-1556 much more effectively blocked the vagus-induced reduction of the heart rate than other tested blocking agents, and, in contrast to the classical ganglion-blocking agents and decamethonium, did not reduce the arterial blood pressure. In addition, IEM-1556 was less effective than hexamethonium in blocking synaptic transmission through the SCG. IEM-1893 and IEM-1848 demonstrated lower efficacy in blocking SCG transmission, if compared with that of IEM-1556. The results suggest that IEM-1556 is a highly selective blocking agent for parasympathetic versus sympathetic pathways, and its selectivity is determined by the presence of a decyl aliphatic radical in its molecule.Neirofiziologiya/Neurophysiology, Vol. 27, No. 5/6, pp. 323–330, September–December, 1995.     

Factors involved in the stimulation of parasympathetic nerve outgrowth.

Nerve growth from the mouse parasympathetic submandibular ganglion is stimulated by the developing target epithelium. To investigate the nature of this trophic influence, homogenates of salivary glands, gland-conditioned medium, and formalin-fixed glands were assayed for ability to elicit parasympathetic axon extension in tissue culture. Neither homogenates nor conditioned medium stimulated axon outgrowth from submandibular ganglia. However, when ganglia were added to glands in which protein synthesis and cell movement had been halted by formalin fixation, stimulation of outgrowth into the tissue was observed. Stimulation of axonal growth occurred after hyaluronidase and collagenase treatment of the glands, but not after treatment with proteases or with heat. Moreover, prolonged formalin fixation destroyed the glandular ability to elicit axon elongation. Intact ganglia cultured with whole live submandibular glands in the presence of low levels of hyaluronidase or collagenase showed extensive axon outgrowth despite disruption of the normal morphogenetic pattern of both epithelium and axons. Our results suggest that stimulation of axon outgrowth does not directly depend on the concomitant metabolic or morphogenetic activity of the epithelium, but is caused by some epithelial product, probably a protein.     

Cardiovascular and sympathetic response to exercise after long-term beta-adrenergic blockade.

The response to dynamic exercise was investigated in 21 patients receiving long-term treatment with beta-adrenoceptor antagonists and 22 controls. An electrocardiogram (ECG) and blood pressure were recorded before and after treadmill exercise, and plasma dopamine-beta-hydroxylase (DBH) activity was measured as an index of changes in sympathetic activity. Heart rate and blood pressure were lower at rest and throughout exercise in treated patients, although the pressor effect of exercise was not reduced. The ECG P-R interval was lengthened, and in addition the Q-T interval was prolonged. After exercise, plasma DBH activity was significantly increased in controls but not in treated patients. We conclude that long-term administration of beta-adrenergic blockers increases myocardial repolarisation time and reduces sympathetic nervous activity. These actions may contribute to the antiarrhythmic and hypotensive effects of long-term beta-blockade.     

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.     

Two-component responses to sympathetic nerve stimulation in the rat tail artery

Membrane potential and tension were recorded simultaneously from the smooth muscle of the rat tail artery. A single stimulus to the perivascular nerves caused a tension transient. The tension transient had two components, one due to a muscle action potential and one due to alpha-adrenoceptor activation. During trains of stimuli most of the tension was due to alpha-receptor activation, even when every stimulus caused a smooth muscle action potential.     

Conditioning of inhibition of sympathetic nerve discharge to stimulation of A- and C-fibres in the aortic nerve

Stimulation of either A- or C-fibres in the aortic nerve inhibits sympathetic nerve discharge (SND) recorded from the renal nerve in rabbits anaesthetized with urethane. When the test inhibition of SND to stimulation of A-fibres is preceded by conditioning stimulation of the same afferents, the test response is depressed at shorter and facilitated at longer testing intervals. Facilitation of the inhibition of SND reaches 120% of control at a testing interval of 10 s. The recovery curve of inhibition of SND to activation of A-fibres has a time course of 17 s. Following conditioning activation only depression of the test inhibition of SND to stimulation of C-fibres is seen. It reaches 46% of control at an interval of 2 s and the recovery curve of inhibition of SND to stimulation of C-fibres has a time course of about 30 s. In other series of experiments the duration of the conditioning stimulation was varied while the testing intervals were fixed. At a testing interval of 2 s the reductions of the test responses are deeper and the durations of conditioning at which plateaus of depression are reached are longer with stimulation of C- than of A-fibres. Taken together with a longer recovery curve these findings suggest a more effective control of the test inhibition of SND by C-fibres. Opposite changes in the patterns of inhibition of SND to activation of either A- or C-fibres are explained by frequency-dependent post-tetanic effects of the conditioning stimulation.     

Effect of sympathetic nerve stimulation on myocardial reactive hyperemia

It has been established in experiments on 25 dogs that the peak of reactive hyperemia (RH) of the myocardium cannot be regarded as an absolute criterion of the coronary dilatory reserves. Stimulation of the stellate ganglion under the conditions of arterial blood pressure stabilization increased the peak of RH. After-effect of the sympathetic nerve stimulation also led to a rise in the peak of RH as compared with control.