Submandibular Gland Blood Flow Research Articles

Differences in salivary secretory function between patients with erosive esophagitis and those with nonerosive reflux disease

It has been speculated that impaired salivary flow contributes to abnormal acid clearance in patients with erosive esophagitis (EE). For easy and objective assessment of salivary function, we developed a salivary gland blood flow measurement technique using continuous-wave Doppler sonography. In the present study, we evaluated the salivary secretory function in patients with EE and those with nonerosive reflux disease (NERD) using this method. Doppler waveform analysis was performed on the facial artery to assess blood inflow to the submandibular gland of 30 healthy subjects (HS). Blood flow was compared before and after secretory stimulation with 1mL of lemon juice. Saliva was simultaneously collected and weighed before and after stimulation. Continuous-wave Doppler sonography was also performed in patients with EE and NERD. The size of the submandibular gland was compared in 26 patients with EE, 41 patients with NERD, and 86 HS. The submandibular gland blood flow increased after stimulation in all HS. Both within-day and day-to-day reproducibility were good. There was a significant correlation between the percent increase in the maximum velocity and the percent increase in salivary secretion. Although the size of the submandibular gland was not significantly different among the three groups, the percent increase in the maximum velocity in patients with EE was significantly smaller than that in HS. We have established an easy method of assessing salivary function in daily practice. This study revealed that a decrease in salivary secretory function is involved in the pathology of EE.

Partial agonistic effects of pilocarpine on Ca(2+) responses and salivary secretion in the submandibular glands of live animals.

What is the central question of this study? Pilocarpine stimulates salivary secretion via muscarinic ACh receptors (mAChRs), although the Ca(2+) -mobilizing effect of pilocarpine in salivary gland cells is extremely small. Therefore, we examined the effect of pilocarpine on Ca(2+) responses in submandibular gland cells and on secretion in vitro and in vivo. What is the main finding and its importance? Pilocarpine induces small Ca(2+) responses and reduces the effects of other mAChR agonists on Ca(2+) responses via its partial agonistic effects. These effects of pilocarpine on Ca(2+) responses in the submandibular gland were further established in vivo with a novel Ca(2+) imaging system and a genetically encoded Ca(2+) indicator. Pilocarpine stimulates salivary secretion via muscarinic ACh receptors (mAChRs), although the effect of pilocarpine on Ca(2+) responses in dispersed salivary gland cells is extremely small. Here, we demonstrate the effect of pilocarpine on Ca(2+) responses and salivary secretion in the rat submandibular gland (SMG). In fura-2-loaded SMG cells, the maximal effect of pilocarpine on [Ca(2+) ]i elevation was 16% of that of carbachol, and pilocarpine attenuated carbachol- and bethanechol (Bet)-induced [Ca(2+) ]i increases, indicating that pilocarpine acts as a partial agonist for mAChR-mediated Ca(2+) responses. The partial agonistic effect of pilocarpine on Ca(2+) dynamics in the SMG was also confirmed in live animals using the genetically encoded Ca(2+) indicator, YC-Nano50. Administration of pilocarpine (3mgkg(-1) , i.p.) elicited a small increase in [Ca(2+) ]i in the SMG. Quantitative analyses demonstrated that resting [Ca(2+) ]i was ∼37nm, which was increased by pilocarpine (3mgkg(-1) ) and Bet (10mgkg(-1) ) to 44 and 69nm, respectively. The inhibitory effects of pilocarpine on Bet-induced Ca(2+) responses were also elucidated in vivo. We further examined real-time changes in pilocarpine-induced SMG salivary secretion and showed that pilocarpine induced an extremely weak secretory response and reduced Bet-induced secretion. Unlike Ca(2+) responses, pilocarpine failed to reduce the effect of Bet on SMG blood flow. Our results demonstrate that pilocarpine acts as a partial agonist of mAChRs to induce weak salivary secretion that is correlated with small increases in [Ca(2+) ]i . Furthermore, pilocarpine exhibits an antagonistic effect on mAChR-induced Ca(2+) responses and salivary secretion.

Role of kinin in regulation of rat submandibular gland blood flow.

In tissues rich in kallikrein, vasodilator kinins, acting as paracrine hormones, may play a role in the local regulation of blood flow. We studied the role of kinins in the regulation of blood flow in the rat submandibular gland using a kinin analogue with antagonistic properties, [DArg0]Hyp3-Thi5-8[DPhe7]bradykinin. When infused into the carotid artery (20 micrograms/min/rat), this antagonist blocked the effect of bradykinin (25-250 ng/kg, intracarotid injection) on glandular blood flow. In nephrectomized rats, the antagonist also blocked the increase in glandular blood flow caused by enalaprilat, a kininase II converting enzyme inhibitor. At a dose of 20 micrograms/min/rat, the antagonist produced no detectable change in basal glandular blood flow; however, at a higher dose (100 micrograms/min/rat), it caused a significant decrease (p less than 0.001). In eight of 10 rats, blood flow decreased by 75% or more; this effect was not blocked by the alpha-adrenergic receptor antagonist phentolamine. After antagonist infusion was stopped, blood flow returned toward normal. Sympathetic nerve stimulation of the gland induced vasoconstriction followed by poststimulatory vasodilatation. In rats displaying severe vasoconstriction after the antagonist, postsympathetic vasodilatation was abolished even when stimulation was performed after the antagonist infusion had been stopped and blood flow returned toward normal. Although a direct vasoconstrictor effect of the kinin antagonist cannot be completely ruled out, these data suggest that, in the rat submandibular gland, kinins may play a role in regulation of basal blood flow and vasodilatation after converting enzyme inhibitor or sympathetic stimulation.

VIP and noncholinergic vasodilatation in rabbit submandibular gland

The effect of parasympathetic nerve activation on rabbit submandibular gland (SMG) blood flow and saliva secretion were studied before and after systemic administration of atropine or hexamethonium. The parasympathetic fibers were stimulated electrically (2 and 15 Hz, 10 V, 1 msec) at the plexus around the submandibular salivary duct or at the chorda lingual nerve. In untreated animals, stimulation of parasympathetic fibers caused a frequency-dependent increase of salivary secretion and blood flow in the SMG. Atropine treatment completely abolished saliva secretion at 2 Hz and 15 Hz and the increase in SMG blood flow during stimulation at 2 Hz. Although atropine significantly reduced the vasodilatory response at 15 Hz, the highest blood flow measured under such circumstances was still about 2.5 times the prestimulation value. After hexamethonium administration no blood flow increase or saliva secretion was seen upon chorda lingual stimulation. The concentration of vasoactive intestinal polypeptide (VIP)-like immunoreactivity in the venous effluent of the SMG increased during nerve stimulation. Atropine significantly reduced, and hexamethonium abolished this VIP-output elicited by parasympathetic nerve stimulation. Local infusion of VIP, peptide histidine isoleucine (PHI) and substance P all caused atropine-resistant vasodilation but no salivation. The present data suggest that VIP and possibly PHI play a role in the atropine-resistant vasodilatation in rabbit submandibular gland elicited by parasympathetic nerve stimulation. The contribution of sensory mediators such as substance P released by stimulation of afferent nerves in the chorda lingual nerve to the salivary and vasodilatory responses seems to be of minor importance in the rabbit submandibular gland.

Effect of sodium restriction and corticosteroids on glandular kallikrein in plasma and in the submandibular gland.

We investigated whether sodium restriction or mineralocorticoid influence the release of submandibular kallikrein into the blood and/or the concentration of kallikrein in glandular tissue. For this we measured submandibular gland blood flow, arterial and submandibular gland venous kallikrein, and kallikrein in glandular homogenates of male Sprague-Dawley rats after one week of either low sodium or deoxycorticosterone acetate (DOCA) treatment. We also studied the effect of dexamethasone on the concentration of kallikrein in gland tissue and peripheral plasma. Kallikrein in plasma and in homogenates was measured by radioimmunoassay. Blood flow was determined by timed collections of venous outflow. Kallikrein release was calculated as the arteriovenous difference in kallikrein times the rate of submandibular gland plasma flow. The concentration of kallikrein in arterial plasma, the basal submandibular kallikrein release into blood, and the concentration of kallikrein in submandibular gland tissue were all higher during low sodium than during normal sodium intake (20.1 +/- 3.6 ng/ml vs 10.7 +/- 0.5, p less than 0.05; 0.40 +/- 0.09 ng/min/100 g bw vs 0.18 +/- 0.02, p less than 0.05, and 81.6 +/- 5.5 micrograms/mg protein vs 65.1 +/- 4.0, p less than 0.05, respectively). In contrast, DOCA treatment did not affect the concentration of kallikrein in arterial plasma, the basal release of kallikrein from the submandibular gland into blood, or the concentration of kallikrein in the gland. Dexamethasone in doses that did not affect the normal growth of the animals had no significant effect on the concentration of kallikrein either in submandibular gland tissue or in peripheral plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the autonomic nervous system in the release of rat submandibular gland kallikrein into the circulation.

We have previously demonstrated that the rat submandibular gland releases immunoreactive kallikrein into the circulation. To study the role of the autonomic nervous system in this release, submandibular gland blood flow and kallikrein concentration in peripheral arterial and venous blood from the gland were measured and secretion rates calculated before and after parasympathetic and sympathetic nerve stimulation (8V, 2 msec, 10 Hz) for 1 minute. Immunoreactive kallikrein in plasma was measured by radioimmunoassay, and timed collections of venous outflow were used to measure blood flow. During basal conditions, the unstimulated submandibular gland of the rat released immunoreactive kallikrein into blood at the rate of 0.92 +/- 0.07 ng/min. Parasympathetic stimulation increased blood flow 4-fold (before, 68.5 +/- 8.3 microliters/min; after, 253.5 +/- 76.2; P less than 0.05) without significantly changing immunoreactive kallikrein secretion rate. Sympathetic stimulation produced an 11-fold increase in blood flow (before, 64.9 +/- 9.3 microliters/min; after, 709.6 +/- 97.5; P less than 0.05) and a 57-fold increase in immunoreactive kallikrein secretion rate from the gland (before, 1.05 +/- 0.25 ng/min; after, 59.8 +/- 18.6; P less than 0.05). Sympathetic stimulation also produced a 4-fold increase in the concentration of immunoreactive glandular kallikrein in arterial plasma (before, 15.2 +/- 1.1 ng/ml; after, 56.2 +/- 12.9; P less than 0.05). Pretreatment with phentolamine (1 mg/kg) or prazosin (0.2 mg/kg) blocked the increase in kallikrein secretion rate produced by sympathetic stimulation. These results indicate that the sympathetic nervous system, through activation of alpha 1-adrenoreceptors, controls kallikrein secretion from the submandibular gland into the circulation. Released kallikrein may be responsible for the reactive vasodilation observed in the rat submandibular gland after sympathetic stimulation.

Kallikrein-kinin system in regulation of submandibular gland blood flow.

Kallikrein-kinin system in regulation of submandibular gland blood flow.

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.

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

The effects of parasympathetic and sympathetic nerve stimulation on VIP release in relation to blood flow and secretion were studied in the cat submandibular salivary gland. Parasympathetic nerve stimulation caused a marked VIP overflow (over thousand fold increase in VIP output) into the venous effluent from the gland which was simultaneous with profuse salivation and an about 10-15 fold increase in blood flow. The VIP output was dependent on the stimulation frequency, the duration of the stimulation period as well as the glandular blood flow. At 15 Hz maximal VIP output (about 4 fmol per impulse) was obtained after about 5 min of stimulation simultaneously with the maximum of the maintained phase of vasodilation. About 50 pmol VIP was recovered in the venous effluent from the gland during 1 h of maximal nerve stimulation. The VIP output after 1 h, was only about 20% of maximal, however, suggesting that the storage reserves and/or resupply of VIP might be running out. Under physiological conditions (frequencies less than or equal to 6 Hz) it was estimated that the axonal transport mechanism should be sufficient for replacement of VIP. At lower frequencies (2 and 6 Hz) the VIP output was parallel to vasodilation and secretion, while at a high frequency (15 Hz) a much more pronounced VIP output was seen. The increased overflow at 15 Hz may either be due to an actual increase in release or to a saturation of local VIP inactivating mechanisms. When stimulated simultaneously, the parasympathetic vasodilator mechanism seemed much more potent than sympathetic vasoconstriction. Since VIP may be present in cholinergic neurons, data from the literature concerning acetylcholine release are discussed in relation to the observed VIP output.

Complementary role of vasoactive intestinal polypeptide (VIP) and acetylcholine for cat submandibular gland blood flow and secretion. II. Effects of cholinergic antagonists and VIP antiserum.

The effects of atropine and hexamethonium on submandibular vasodilation, secretion and VIP release in response to parasympathetic nerve stimulation were studied in cats. It was found that salivary secretion was completely atropine sensitive at all frequencies. The vasodilatory response was characterized by an initial phase (most marked at lower frequencies) followed by a maintained phase (most pronounced at high frequencies). Atropine reduced the initial phase at all frequencies while the maintained phase was reduced only at low stimulation frequencies. At 15 Hz the maintained blood flow response was paradoxically increased after atropine, particularly with regard to the duration. The increase in blood flow after atropine was accompanied by an about eight fold increase in VIP output as compared to control stimulations at 15 Hz. This may suggest that the acetylcholine levels regulate the VIP release in a feed-back system via muscarinic autoreceptors. No increase in VIP output by atropine was, however, observed at 2 Hz while a small but significant increase was found at 6 Hz. Treatment with VIP antiserum reduced both phases of the vasodilation as well as the secretion in response to stimulation at 2 Hz. Thus, VIP and acetylcholine seem to be important for both phases of vasodilation as well as for salivary secretion. The relative contributions of VIP and acetylcholine are, however, hard to evaluate since atropine appears to increase VIP release. This fact complicates the characterization of cholinergic and noncholinergic vasodilator mechanisms by the use of atropine. Hexamethonium treatment abolished both the vasodilation, the secretion and the VIP release seen during parasympathetic nerve stimulation implying that it was preganglionic and that the preganglionic transmitter is acetylcholine which activates postganglionic transmitter is acetylcholine which activates postganglionic neurons via nicotinic receptors. Somatostatin had no blocking effect on parasympathetic mechanisms in the cat submandibular gland.