Blood Flow and Interstitial Fluid Pressure in the Rat Submandibular Gland during Changes in Perfusion

The submandibular gland is a cell-rich encapsulated organ with high transport of fluid through the interstitial space during salivation. We hypothesized that the gland is a low-compliant tissue, i.e., that a modest increase in fluid volume will produce a rise in interstitial fluid pressure (IFP) counteracting fluid filtration into the interstitium. To test this hypothesis, we measured IFP with micropipettes and glandular blood flow (GBF) with a laser-Doppler flowmeter during changes in perfusion. Clamping of the carotid artery or the jugular vein, or electrical stimulation of the sympathetic or parasympathetic nerve to the gland, induced changes in perfusion. Baseline IFP averaged 3.5 ± 0.5 mm Hg. Clamping of the artery reduced IFP and GBF (−56.5 ± 8.4% and −53.1 ± 6.4%, respectively), whereas clamping of the vein decreased GBF (−21.6 ± 14.3%) and increased IFP (141.2 ± 27.4%). Sympathetic nerve stimulation reduced both parameters (−86.9 ± 16.5% and −74.4 ± 7.0%, respectively). In contrast, stimulation of the parasympathetic nerve elicited an increase in GBF (133.2 ± 5.9%) and in IFP (173.3 ± 41.4%). Thus, changes in vascular volume led to concomitant changes in IFP consistent with low tissue compliance, a phenomenon of importance for fluid volume regulation.

Modulation of Dental Inflammation by the Sympathetic Nervous System

Recent findings have indicated that immune responses are subjected to modulation by the sympathetic nervous system (SNS). Moreover, the findings show that the SNS inhibits the production of pro-inflammatory cytokines, while stimulating the production of anti-inflammatory cytokines. The present review is an attempt to summarize the current results on how the SNS affects inflammation in dental tissues. In dental tissues, it has been found that the SNS is significant for recruitment of inflammatory cells such as CD 43+ granulocytes. Sympathetic nerves appear to have an inhibitory effect on osteoclasts, odontoclasts, and on IL-1α production. The SNS stimulates reparative dentin production, since reparative dentin formation was reduced after sympathectomy. Sprouting of sympathetic nerve fibers occurs in chronically inflamed dental pulp, and neural imbalance caused by unilateral sympathectomy recruits immunoglobulin-producing cells to the dental pulp. In conclusion, this article presents evidence in support of interactions between the sympathetic nervous system and dental inflammation.

Edema in Oral Mucosa after LPS or Cytokine Exposure

Lowering of interstitial fluid pressure (Pif) is an important factor that explains the rapid edema formation in acute inflammation in loose connective tissues. Lipopolysaccharide (LPS) and the pro-inflammatory cytokines interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) are pathogenetic in gingivitis. To test if these substances induce lowering of Pif in rat oral mucosa, we measured Pif with a micropuncture technique. IL-1β and TNF-α caused lowering of Pif, whereas LPS induced an immediate increase in Pif, followed by lowering after 40 min. Measurements of fluid volume distribution showed a significant change in interstitial fluid volume (Vi) 1.5 hr after LPS exposure as Vi changed from 0.41 ± 0.02 to 0.51 ± 0.03 mL/g wet weight ( p < 0.05), confirming edema. These findings show that LPS, IL-1β, and TNF-α induce lowering of Pif in the rat oral mucosa and contribute to edema formation in LPS-induced gingivitis.

Sympathectomy decreases size and invasiveness of tongue cancer in rats

The sympathetic nervous system plays a role in carcinogenesis wherein locally released sympathetic neurotransmitters affect proliferation, angiogenesis, vessel permeability, lymphocyte traffic and cytokine production. The present in vivo study was designed to investigate whether surgical sympathectomy, both unilateral and bilateral, had an effect on tumor growth, interstitial fluid pressure (IFP) and lymphatics in rat tongue cancer. We used 4-nitroquinoline-1-oxide (4-NQO) in drinking water for 19 weeks to induce tongue cancer in 20 Dark Agouti rats. After 11 weeks, one group underwent unilateral sympathectomy and another underwent bilateral sympathectomy, while the third group underwent sham surgery. By 19 weeks, tumors in the bilaterally sympathectomized (BL-SCGx) rats were significantly smaller (P<0.05), more diffuse in appearance and less invasive (P<0.05) compared with the large exophytic tumors in the sham-operated rats. The relative lymphatic area was significantly decreased (P<0.05) in tumors in the BL-SCGx rats compared with the sham group. Interestingly, the tumors in rats that underwent unilateral or bilateral sympathectomy had a significantly lower (P<0.05) IFP than those in sham rats. Lack of tyrosine hydroxylase (TH) immunoreactive nerves and few neuropeptide Y (NPY) positive fibers indicate absence of sympathetic nerve fibers in the bilateral sympathectomized group. The peritumoral lymph vessel area was correlated with the tumor size (P<0.001), depth of invasion (P<0.001), weight of rats (P<0.005) and IFP (P<0.05). In conclusion, the present study presents evidence that deprivation of sympathetic nerves decreases tumor growth in rat tongue, probably caused by decreasing IFP and lymph vessel area.

Immunoglobulin producing cells in the rat dental pulp after unilateral sympathectomy

Recent studies show that sympathetic nerves participate in immunomodulation. We investigated the effects of unilateral sympathectomy on recruitment of cells expressing kappa and lambda (kappa and lambda) light chains in the rat dental pulp. Superior cervical ganglion was removed in experimental rats (n=10) while control rats (n=8) received sham surgery. Following perfusion 18 days later, mandibular jaws were processed for immunohistochemistry and electron microscopy. Sympathectomy results in recruitment of cells expressing kappa and lambda light chains into the dental pulp (P=0.005). Electron microscopy revealed these cells to be mainly plasma cells and Mott cells. We conclude that neural imbalance caused by unilateral sympathectomy recruits immunoglobulin producing cells in the dental pulp. Our results are in agreement with a model of immune regulation in which the sympathetic nervous system exerts a tonic regulatory effect over lymphocyte proliferation and migration.

Effects of sympathectomy on experimentally induced pulpal inflammation and periapical lesions in rats

The role of sympathetic nerves in bone physiology is largely unknown. Recent studies have shown a correlation between sympathectomy and bone remodeling. The present experiments were aimed to study the effects of unilateral sympathectomy on bilateral experimentally induced pulpitis and periapical lesions in the rat maxilla and mandible. Adult male Sprague-Dawley rats were used. Experimental rats (n=11) had the right superior cervical ganglion surgically removed (SCGx) and control rats (n=5) had sham surgery. Pulpal inflammation and periapical bone lesions in the maxilla and mandible were created 14 days later in both experimental and control rats by exposing the dental pulp in the first and second molars and leaving them open to the oral microflora. The rats were perfused 20 days thereafter and the jaws processed for immunohistochemistry with neuropeptide Y (NPY) and ED1 as primary antibodies. Sympathectomy resulted in an almost complete loss of NPY-immunoreactive (IR) fibers in the right SCGx jaws. In the non-sympathectomized (non-SCGx) left side and in the control rats, sprouting of NPY-IR fiber was observed in the inflamed pulp tissue adjacent to reparative dentin formation and in the apical periodontal ligament of the partially necrotic first molars. Significantly more ED1-IR osteoclasts were found in the resorptive lacunae lining the periphery of the periapical lesions on the SCGx side compared with the non-SCGx side (P<0.04) and the controls (P<0.03). The size of the periapical lesions were larger on the SCGx side compared with the non-SCGx side (P<0.03) in the mandible, but not in the maxilla. We conclude that inflammation causes sprouting of NPY-IR nerve fibers and that unilateral removal of the SCG increases both the area of the periapical lesions and the number of osteoclasts in the inflamed region.

Role of K+ATP channels, endothelin A receptors, and effect of angiotensin II on blood flow in oral tissues

K+(ATP) channels are involved in CGRP-mediated vasodilation and in the vasoconstriction induced by endothelin or angiotensin II. In this study, we examined the effects of a K+(ATP) channel antagonist and an ET(A) receptor antagonist on resting blood flow in the pulp and gingiva, and observed their role in the vasodilation induced by tooth stimulation. We also investigated whether receptors for angiotensin II exist in the pulp and gingiva. Blood flow was measured with laser-Doppler flowmetry. Under control conditions, the K+(ATP) channel antagonist and angiotensin II caused a significant drop in blood flow in both target tissues. Blocking of ET(A) receptor did not change basal blood flow. The vasodilation observed after tooth stimulation remained unchanged following blockade of K+(ATP) channels and ET(A) receptors. Analysis of the data shows that open K+(ATP) channels exist during resting conditions in the pulp and gingiva, but that CGRP seems to induce vasodilation mainly via mechanisms other than K+(ATP) channels. ET(A) and AT(1) receptors are found in the pulp and gingiva, but ET(A) receptors are not involved in modulation of a basal vascular tone in these tissues or in the vasodilation observed after tooth stimulation.

Merkel-like cells in Malassez epithelium in the periodontal ligament of cats: an immunohistochemical, confocal-laser scanning and immuno electron-microscopic investigation

The cellular heterogeneity of Malassez epithelium (ME) residing in the periodontal ligament has recently been reported, and the presence and coexistence of the neuropeptides calcitonin gene-related peptide (CGRP), substance P (SP) and vasoactive intestinal peptide (VIP) in single cells in ME has been shown (1). However, the identity of these neuroendocrine cells has so far not been verified. This study was undertaken in order to elucidate the identity of the neuroendocrine cells in ME by means of transmission electron microscopy, confocal scanning microscopy and immunohistochemistry using antibodies to protein gene product (PGP) 9.5 and cytokeratin 20 (CK). Gingival tissue was included in the study as a positive control for identification of Merkel-like cells in oral epithelium. CK 20 immunopositive cells were present in both Malassez epithelium and in basal cell layers of gingival epithelium showing a distribution consistent with PGP 9.5 labelled cells in both epithelia. The results from PGP 9.5 immuno electron microscopy clearly evidenced the presence of single, intensely labelled cells and some nerve fibres invested between the Malassez epithelial cells. The conformity of the immunopositive cells in Malassez and gingival epithelium verified by double immunolabelling with PGP 9.5 and CK 20, indicates that the labelled neuroendocrine cells are identical in ME and in gingival epithelium. This demonstrates that Malassez epithelium not only exhibits neuroendocrine cells, but additionally that the neuroendocrine cells represent Merkel-like cells.

Effect of denervation on healing after tooth replantation in the ferret

Studies have shown that the sensory nerves participate in inflammation and immune responses and possess trophic-facilitating wound healing in general. Tooth avulsion represents a pulpal and periodontal injury, and the mechanisms involved in the healing responses subsequent to replantation of teeth are still unclear. The objective of this study was to investigate the healing responses after denervation and replantation of teeth. Unilateral denervation was performed in 15 ferrets by axotomy of the inferior alveolar nerve, 5 days before extraction of the first lower premolars. Six weeks later the mandibles were excised and processed for histological evaluation. Immunohistochemistry was performed using antibodies against the sensory neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP), and measurements of root resorption and ankylosis were performed in four sections from each replanted tooth. After 6 weeks substantial reinnervation was observed in the jaws. Immunoreactivity in the pulp was observed in only two replanted teeth on the denervated side, compared with four on the innervated side. Total pulp necrosis appeared in 10 replanted teeth on the denervated side and in 5 on the innervated, indicating that sensory nerves promote survival of the pulp after replantation. SP-immunoreactive (IR) fibers were more frequently observed in the resorptive lacunae than CGRP-IR fibers. However, resorptive areas lacking IR fibers were frequently found along the root surface. Root resorption averaged 0.062 +/- 0.029 mm2 on the innervated side compared to 0.016 +/- 0.0043 mm2 on the denervated (P< 0.02). Ankylosis was observed in four of the replanted teeth on the innervated side (169.3 +/- 49.7 microm) and in six on the denervated side (332.56 +/- 193.2 microm) (P = 1). It is concluded that the sensory nerves promote root resorption after pulpoperiodontal injuries but have less influence on the osteoblastic activity expressed by ankylosis.

Drainage of plasma proteins from the renal medullary interstitium in rats

1. Lymph vessels are scarce or lacking in the renal inner medulla, raising the question of whether plasma proteins entering the medullary interstitium are removed by diffusion through the interstitium to lymphatics in the outer medulla or cortex, or by convection into the vasa recta. 2. Using micropipettes, we infused 125I-albumin into the papilla of anaesthetized rats and watched its disappearance from the injection site as well as the uptake in the thoracic duct and plasma. 3. Tracer infused into the renal cortex appeared almost immediately in the thoracic duct lymph, and rose to a sevenfold higher concentration than in plasma, whereas tracer infused into the papilla appeared first and increased more sharply in plasma than in the lymph. No spread from the papillary injection site was observed. Tracer injected in renal hilar lymphatics was quantitatively recovered in the thoracic duct. 4. The plasma concentration pattern following papillary infusion was similar to that obtained by intravenous injection, indicating uptake in blood and subsequent distribution to extracellular fluid and lymph from all organs. 5. We conclude that plasma proteins normally diffusing out from the vasa recta are brought back through water flux (1) from the collecting ducts due to the high sodium chloride concentration in the papillary interstitium and (2) from the interstitium into the vasa recta driven by plasma protein osmotic pressure. Accordingly, there is no need for lymph vessels in the inner medulla.

Pulp-dentin biology in restorative dentistry. Part 3: Pulpal inflammation and its sequelae

Physiologic and histopathologic experimental studies over the last 30 to 40 years have demonstrated that the healing of the dental pulp is comparable to that of connective tissue elsewhere, despite its location in the low-compliance pulp chamber. The greatest difficulty from a clinical point of view is to assess cellular changes and vitality of the pulp. If it is vital, the potential for repair is present, especially in young individuals.

Pulp-dentin biology in restorative dentistry. Part 1: normal structure and physiology

Considerable knowledge has accumulated over the years on the structure and function of the dental pulp and dentin. Some of this knowledge has important clinical implications. This review, which is the first of seven articles, will be limited to those parts of the normal structure and physiology of the pulp and dentin that have been shown to result in, or are likely lead to, tissue reactions associated with the clinical treatment of these tissues. Although certain normal structures will be highlighted in some detail, a basic knowledge of pulpal and dentinal development and structure is a prerequisite for an understanding of this text.

The effect of unilateral sympathectomy and cavity preparation on peptidergic nerves and immune cells in rat dental pulp

Recent evidence suggests interactions between primary afferent nociceptors and postganglionic sympathetic efferents in the pathogenesis of inflammation. The effect of unilateral removal of the superior cervical ganglion on the innervation pattern of nerve fibers immunoreactive (IR) to calcitonin gene-related peptide (CGRP), substance P (SP), and neuropeptide Y (NPY), as well as the occurrence of immune cells in the injured and uninjured rat molar pulp, was investigated. Light microscopic immunocytochemistry demonstrated that the molar pulps contralateral to the sympathectomy contained a NPY-IR nerve fiber network more dense and heavily stained than unoperated control rats. The NPY-IR fibers showed, however, no sprouting after deep cavity preparation. There was no compensatory increase in CGRP- and SP-IR nerve fibers in the dental pulp after unilateral sympathectomy, although a significant increase in cells IR to CGRP and SP was found in the ipsilateral trigeminal ganglion. Unilateral sympathectomy induced a significant increase in immune cell density both in the inflamed and in the uninflamed dental pulp bilaterally. Our results demonstrate, for the first time, a trophic effect of the sympathetic nerves on immune cells in the dental pulp, indicating that an imbalance of sympathetic nerves may induce inflammation and pain in teeth.

Effect of the sensory neuropeptide antagonists h-CGRP((8-37)) and SR 140.33 on pulpal and gingival blood flow in ferrets

In a previous study, it was concluded that the neuropeptides calcitonin gene-related peptide (CGRP) and substance P are released during resting conditions in the (exposed) ferret dental pulp, contributing to a basal vasodilator tone in the pulpal vessels. In order to exclude the possibility that the method used elicited axon reflexes, which might be responsible for neuropeptide release, the present study was designed without pulp exposure. Non-invasive laser-Doppler flowmetry was used to measure the effects of intra-arterial infusions of the antagonists h-CGRP((8-37)) and SR 140.33 (neurokinin 1-receptor antagonist) on pulpal and gingival blood flow before, during and after electrical tooth stimulation. Infusions of h-CGRP((8-37)) reduced the basal blood flow in the pulp by 31.4+/-5.2% (p<0.001) and in the gingiva by 22.6+/-4.8% (p<0.05). A further significant decrease in basal blood flow was measured in both pulp and gingiva following SR 140.33 administration. The reduction in blood flow was 16.9+/-1.9% (p<0.005) in the pulp and 19. 3+/-5.6% (p<0.05) in the gingiva. The systemic arterial pressure remained unchanged both during and after the periods of infusion. Tooth stimulation before the antagonist infusion significantly increased the pulpal blood flow by 71.9+/-15.3% (p<0.005). Infusion of h-CGRP((8-37)) greatly reduced this electrically induced vasodilatation, indicating that CGRP is the principal factor responsible for the vasodilatation observed after tooth stimulation. This study confirms the previous finding that a resting vasodilator tone due to the release of CGRP and SP exists in the ferret dental pulp. It is concluded that spontaneous, basal release of the neuropeptides CGRP and substance P exists both in dental pulp and gingiva in the ferret.

Neuroendocrine cells in Malassez epithelium and gingiva of the cat

Malassez epithelium has been designated as epithelial cell rests, the biological significance of which is still under debate. This study was designed to analyze Malassez epithelium for the presence of neuroendocrine cells. Gingival tissue was included as a positive control. Using immunohistochemistry, confocal and light microscopy, Malassez epithelium and gingival epithelium from mature cats (n = 5) were examined for cells containing the neuropeptides calcitonin gene-related peptide (CGRP), substance P (SP), and vasoactive intestinal peptide (VIP). Both Malassez epithelium and the basal epithelial cell layers in gingival rete pegs regularly displayed cells immunoreactive to CGRP, SP, and VIP. The immunopositive cells were most frequently present in the epithelial cell clusters and strands of Malassez located in the cervical half of thc periodontal ligament. Double immunolabeling revealed cellular co-expression of CGRP or SP with VIP, and the neuropeptides were co-localized in the cellular compartments. Labeled cells in both epithelia were occasionally supported by immunoreactive nerve fibers. This study shows that cells immunoreactive to CGRP, SP, and VIP arc located within the cat Malassez epithelium. The localization of neuroendocrine cells verifies the diversity of this epithelium and confirms that Malassez epithelium is composed of different cell types, in common with epithelia from other locations. The presence of neuroendocrine cells in Malassez epithelium strongly suggests biological functions of this tissue, and the neuropeptide content may thus indicate endocrine functions of the cells.

Interstitial fluid pressure in normal and inflamed pulp

Tissue pressure is the hydrostatic pressure in the interstitial fluid which surrounds the pulpal cells. This pressure outside the vessels is normally considerably lower than the blood pressure inside the vessels. The dental pulp has a relatively low interstitial compliance due to its enclosure between rigid dentin walls. Accordingly, even a modest increase in pulpal fluid volume will raise the tissue pressure, which may compress blood vessels, leading to ischemia and necrosis. Inflammation may lead to an increase in both interstitial fluid volume and blood volume in the low-compliant pulp and thereby increase the tissue pressure. However, the increased tissue pressure may, in turn, initiate increased lymph flow and absorption of fluid into capillaries in nearby non-inflamed tissue. Both of these latter factors will transport fluid out of the affected area and subsequently out of the tooth and consequently lower the tissue pressure. Increased tissue pressure, whether caused by increased blood volume or increased capillary filtration, will promote outward flow of fluid through exposed dentin tubules and thereby help to protect the pulp against entry of harmful substances. It seems physiologically beneficial, therefore, for the pulp to have a high tissue pressure, which promptly increases when blood flow increases due to its low compliance.

The role of sensory neuropeptides and nitric oxide on pulpal blood flow and tissue pressure in the ferret

A study was designed to investigate the effects of close intra-arterial infusion of antagonists to the sensory neuropeptides calcitonin gene-related peptide and substance P, as well as the effect of the nitric oxide synthesis inhibitor L-NAME on pulpal blood flow and interstitial fluid pressure during resting conditions and after electrical tooth stimulation. The micropuncture technique was used to measure tissue pressure and laser-Doppler flowmetry for blood flow recordings in ferret canine teeth. Close intra-arterial infusion of antagonists to calcitonin gene-related peptide and substance P significantly reduced resting blood flow (p < 0.05) and interstitial fluid pressure (p < 0.005) by unchanged systemic arterial pressure, while L-NAME administration caused a significant rise in interstitial fluid pressure (p < 0.05) and systemic arterial pressure (p < 0.005), with a concomitant fall in resting blood flow (p < 0.005). Tooth stimulation after calcitonin gene-related peptide antagonist infusion gave no significant change in blood flow or interstitial fluid pressure, whereas substance P antagonist infusion only partly eliminated the vasodilator response. L-NAME had no effect on the vasodilation induced by tooth stimulation. It is concluded that a resting vasodilator tone due to release of calcitonin gene-related peptide, substance P, and nitric oxide exists in the ferret dental pulp. The sensory neuropeptides exert their effect predominantly on pre-capillary vessels, and nitric oxide predominantly on post-capillary vessels. The sensory neuropeptide calcitonin gene-related peptide seems to be mainly responsible for the increase in blood flow and interstitial fluid pressure during tooth stimulation, whereas there was no evidence that nitric oxide participates in the vasodilation induced by tooth stimulation.

Nerve fibers immunoreactive to calcitonin gene-related peptide, substance P, neuropeptide Y, and dopamine beta-hydroxylase in innervated and denervated oral tissues in ferrets

The effect of sensory and sympathetic denervation on the localization and distribution of nerve fibers immunoreactive (IR) to calcitonin gene-related peptide (CGRP), substance P (SP), neuropeptide Y (NPY), and dopamine beta-hydroxylase (DBH) was studied in the dental pulp, periodontal ligament (PDL), and gingiva in ferrets. Unilateral axotomy was performed by resection of the inferior alveolar nerve (IAN) 10 days before the experiment (Group 1); sympathectomy, by unilateral removal of the cervical ganglion 5 days before the experiments (Group 2). Immunohistochemistry was performed on free-floating sections by the avidin-biotin-peroxidase technique. A considerably higher density of sensory fibers IR to CGRP and SP was found in the dental pulp than in PDL and gingiva. The majority of pulpal fibers were located in the walls of blood vessels. A subodontoblastic network of fibers IR to CGRP and SP was lacking in incisors and canines and was found only in the coronal pulp in premolars and molars. Sympathetic fibers were sparsely distributed in the pulp, and they were mainly confined to large vessels running centrally in the root pulp as well as the larger vessels in apical PDL and alveolar bone. Gingiva was well supplied with CGRP- and SP-IR nerves, and some NPY and DBH fibers were located in association with larger vessels. Round cell-like structures within the basal part of the epithelium were CGRP-IR. Axotomy induced a complete loss of CGRP- and SP-IR fibers in the anterior part of the jaws, whereas sympathectomy caused a reduction, but not a total loss, of NPY- and DBH-IR nerves. It is concluded that, except for some distributional differences, the oral tissues in the ferret have an abundant sensory innervation similar to that found in other species.

Micropuncture measurements of interstitial fluid pressure in rat nasal mucosa during early inflammatory reactions

Interstitial fluid pressure (Pif) has been studied in rat nasal mucosa during early inflammatory reactions induced by dextran anaphylaxis and local application of histamine. Pif was measured by using sharpened micropipettes connected to a servo-controlled counterpressure system. Access to the nasal mucosa was obtained from the facial side of the head through a small cavity drilled in the nasal bone. During dextran anaphylaxis, Pif increased significantly from control values of 2.2 +/- 0.4 to 3.8 +/- 0.21 mmHg (P < 0.05) within 1 h. Corresponding Pif values for histamine were 1.6 +/- 0.9 and 2.9 +/- 0.9 mmHg (P < 0.05), respectively. These measurements support the hypothesis that a major driving force for the rapid exudation across inflamed respiratory mucosa is a hydrostatic pressure gradient created by increased mucosa Pif. When the transvascular fluid shifts accompanying the inflammatory reactions are prevented by circulatory arrest, Pif decreased significantly to subatmospheric values, -0.8 +/- 0.8 and -3.3 +/- 1.2 mmHg in the dextran and histamine group, respectively (P < 0.05). The decrease in Pif in the nasal mucosa after inflammatory stimuli, during circulatory arrest, provides further evidence for "active" modulation of Pif through changes in mechanical properties of the interstitial matrix. The decrease in Pif seen under these circumstances reveals a possible mechanism participating in the rapid and initial edema formation after inflammatory provocations.

Effect of intermittent long-lasting electrical tooth stimulation on pulpal blood flow and immunocompetent cells: a hemodynamic and immunohistochemical study in young rat molars

Release of sensory neuropeptides after stimulation of afferent nerve fibers has previously been shown to induce vasodilation and increased vascular permeability in the dental pulp, a condition recognized as neurogenic inflammation. In the present study a possible role for the sensory neuropeptides in transendothelial migration of immunocompetent cells was investigated. The dental pulp is an isolated tissue densely innervated with sensory fibers containing neuropeptides, and following electrical stimulation of the crown, the effect on pulpal blood flow and immunocompetent cells can be studied in a noninvasive model. A laser Doppler flowmeter was used to measure relative changes in pulpal blood flow during long-lasting intermittent stimulation of innervated and denervated rat first molars. In the innervated teeth, stimulation promptly increased pulpal blood flow by on average 45% at the start of the experiment, whereas almost no blood flow increase was recorded after 4 to 5 h stimulation. Surgical sectioning of the inferior alveolar nerve abolished blood flow increase upon stimulation. After stimulation, a quantitative analysis of CD43+, CD4+, CD11+, and I-A antigen-expressing cells was performed, and the effect of stimulation on calcitonin gene-related peptide (CGRP)-immunoreactive and substance P (SP)-immunoreactive (IR) nerve fibers was studied. Immunohistochemistry was performed by the avidin-biotin peroxidase method. Stimulation resulted in an almost complete depletion of CGRP- and SP-IR nerve fibers in the first molar pulp, whereas nerve fibers in the gingiva and neighboring teeth were unaffected. A significant increase in the number of CD43+ cells was found in the innervated tooth after stimulation compared to the stimulated denervated (P < 0.01) and unstimulated control (P < 0.05) first molars. For I-A antigen-expressing cells a significant increase (P < 0.05) was found between the innervated stimulated and unstimulated control, but not between the innervated and denervated stimulated first molars. Hence, from the present experiment it is concluded that the pulpal nerves participate in and facilitate transendothelial migration of CD43+ cells during acute neurogenic inflammation.

Pulp interstitial fluid pressure and blood flow after denervation and electrical tooth stimulation in the ferret

The effects of sensory and sympathetic denervation on simultaneously measured interstitial fluid pressure and blood flow in the canine pulp before, during and after electrical tooth stimulation were investigated in 25 ferrets. The micropuncture technique was used to measure interstitial fluid pressure and laser-Doppler flowmetry was used to record pulpal blood flow. Animals with an intact innervation (group 1) served as controls. Sensory denervation was by axotomy of the left inferior alveolar nerve 10 days before the experiment (group 2) and sympathectomy by removal of the left cervical ganglion 5 days before the experiments (group 3). The study was designed to verify whether denervation affected basal pulp blood flow and interstitial fluid pressures during control conditions and/or after tooth stimulation. During control conditions the interstitial fluid pressure averaged 1.32 +/- 0.07 kPa in group 1, whereas the mean was only 0.51 +/- 0.13 kPa in the axotomized animals (group 2). The difference was highly significant, indicating decreased blood or interstitial fluid volume in the pulp after inferior alveolar nerve axotomy. In the sympathectomized group neither the interstitial fluid pressure nor the pulp blood flow was significantly different from those of group 1. Electrical tooth stimulation caused an almost simultaneous increase in interstitial fluid pressure and pulp blood flow in groups 1 and 3, whereas stimulation did not significantly change either variable in the axotomized animals (group 2). It is concluded that a resting nervous vasodilator tone of sensory origin exists in the ferret dental pulp, and that the sensory nerves are responsible for the increased interstitial fluid pressure and pulp blood flow during tooth stimulation.

Neuropeptide Y expression in the trigeminal ganglion and mandibular division of the trigeminal nerve after inferior alveolar nerve axotomy in young rats

Neuropeptide Y (NPY) is a 36-amino-acid peptide residing in sympathetic nerve terminals, originating from the superior cervical ganglion in oral tissues. NPY exerts vasoconstrictor action together with noradrenalin and has been found to inhibit the release of neurotransmitters from primary afferent fibers. During regeneration of the axotomized inferior alveolar nerve (IAN), NPY-immunoreactive (IR) nerve fibers have been shown in the odontoblast layer and dentin, an area normally innervated by afferent nerve fibers. The dynamic shift in neuropeptide expression in the trigeminal ganglion and in the dental pulp was studied by immunohistochemistry 1, 2, 3, and 8 weeks after IAN axotomy. In the ipsilateral first mandibular molar a temporal loss of pulpal sensory nerves lasting for approximately 1 week was found after axotomy. An upregulation of NPY was shown in neurons located in the mandibular area of the trigeminal ganglion, concomitant to a reduction in number of neurons expressing substance P (SP). To study an alternate and possible trigeminal origin of some of the peripheral nerve fibers IR to NPY in the dental pulp, double immunofluorescence labeling was performed for NPY and calcitonin gene-related peptide (CGRP). Coexistence of NPY and CGRP was shown in neurons located in the trigeminal ganglion and in nerve fibers in the tooth pulp during IAN regeneration. Furthermore, retrograde tracing with Fluorogold revealed NPY-IR neurons projecting to the first molar pulp 3 weeks after axotomy. Hence, we conclude that after IAN axotomy NPY is produced in trigeminal ganglion neurons and transported in afferent regenerating fibers to the dental pulp. These results add further evidence for a plasticity in peptide transcription in sensory neurons after nerve injury and indicate a trigeminal origin of at least some of the pulpal NPY-IR fibers during nerve regeneration.

Effect of capsaicin treatment or inferior alveolar nerve resection on dentine formation and calcitonin gene-related peptide- and substance P-immunoreactive nerve fibres in rat molar pulp

The aim of this study was to investigate whether decreased sensory innervation induced by capsaicin treatment or axotomy of the inferior alveolar nerve has an effect upon dentine formation in the rat first molar. Dentine formation was visualized by intravital injection of Procion brilliant Red H8BS and denervation was verified immunohistochemically for the neuropeptides calcitonin gene-related peptide (CGRP) and substance P. The observation times were 6 weeks for the capsaicin-treated group and 11 days for the axotomized group. Capsaicin injections caused a consistent reduction in numbers of CGRP- and substance P-immunoreactive fibres in the pulps and a somewhat smaller reduction in the periodontal tissues. Unilateral axotomy of the inferior alveolar nerve induced an almost complete loss of immunoreactive fibres in the pulp and in the mesial gingiva of the first molar. Dentine formation at the mesial pulp horn and at the central pulp floor was significantly reduced in both groups compared to controls. The results suggest that sensory neuropeptides such as CGRP and substance P may play a part in dentine formation.

Effect of inferior alveolar nerve axotomy on immune cells and nerve fibres in young rat molars

Denervation has been a useful approach to the investigation of interactions between nerve fibres and the pulp-dentine complex. Information on the immunological implications of axotomy is still lacking. The effect of axotomy on CD43+, CD4+, CD11b+ and I-A antigen-expressing cells in both the distal segment of the cut inferior alveolar nerve and in the first molar pulp of young rats was evaluated. Nerve fibres immunoreactive to protein gene product (PGP) 9.5, the neuropeptides substance P and calcitonin gene-related peptide (CGRP), and neuropeptide Y were visualized also by use of the avidin-biotin peroxidase complex method. Recruitment of macrophages was found in the distal segment of the sectioned inferior alveolar nerve 2 days after axotomy, with a further increase in number during the 6-day observation period. However, in the dental pulp, the number of CD43+, CD4+, CD11b+ and I-A antigen-expressing cells was almost unaffected. An almost complete sensory denervation of the first mandibular molar pulp was obtained 2 days after axotomy. After 6 days, the mesial part of the coronal pulp still remained denervated, while regenerated nerve fibres had reached both the root pulp and the distal part of the coronal pulp. Nerve fibres immunoreactive to neuropeptide Y were slightly reduced in density 2 days after axotomy, and after 6 days the localization of neuropeptide Y-immunoreactive fibres was changed compared to the control, with fibres also distributed in the odontoblast layer close to dentine. Hence, following axotomy in young rats, an almost complete sensory denervation is achieved in the first molar, whereas nerve fibres immunoreactive to neuropeptide Y change their distribution pattern, with fibres located close to the dentine after 6 days. Due to the almost unchanged number and distribution of immunocompetent cells in the pulp after axotomy, the young rat molar pulp may represent a suitable and useful experimental model to study neuro-immune interactions.

Recruitment of immunocompetent cells after dentinal injuries in innervated and denervated young rat molars: an immunohistochemical study

The dental pulp represents a peripheral end-organ deprived of a collateral nerve supply. After inferior alveolar nerve (IAN) axotomy, rat molar pulp is denervated over a period of at least 6 days. Therefore, rat molar pulp was used as an experimental model to study the effect of sensory nerve fibers on influx of immunocompetent cells after dentinal injury. In the present study we performed a quantitative analysis of CD43+, CD4+, CD11b+, and I-A antigen-expressing cells subjacent to dentinal cavities in denervated and innervated first mandibular molars. For visualization of nerve fibers, antibodies to protein gene product (PGP) 9.5, the sensory neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP), and the sympathetic neuropeptide Y (NPY) were used. Immunohistochemistry was performed by the avidin-biotin-peroxidase method. In the innervated teeth, a correlation between increased sensory nerve density and influx of immunocompetent cells was found. Compared to the contralateral innervated molars, a significant reduction in recruitment of immunocompetent cells was found in the denervated pulp tissue subjacent to the dentinal cavities. The rat molar represents a unique model to illustrate the influence of sensory nerves and neuropeptides on inflammation and recruitment of immunocompetent cells.

Effect of venous stasis and hypoproteinemia in gingival fluid formation in rats

Experiments were performed to provide information on the mechanisms of the formation of gingival fluid in rats and on the determinants of its flow and composition. For this purpose we studied the effect of increasing net capillary filtration by venous stasis induced by multiple ligations of the jugular vein or by hypoproteinemia induced through puromycine nephrosis. A 1 microliter glass capillary was placed in the sulcus of the first maxillary molar for collection of gingival fluid (GF). Colloid osmotic pressure (COP) was determined in GF, in wick fluid from attached gingiva and buccal mucosa, and in plasma. Interstitial fluid hydrostatic pressure (Pi) was measured by micropuncture technique and the fractional removal rate of radio-labelled human serum albumin (kAlb) was recorded in attached gingiva and buccal mucosa. During venous stasis the gingival fluid flow increased from 1.7 microliters/h to 3.8 microliters/h, whereas COPGF fell from 14.1 mmHg to 8.8 mmHg. COP in wick fluid from gingiva was reduced from 10.3 to 4.3 mmHg. Pi increased from 6.8 to 13.1 mmHg, and kAlb in sham-operated controls increased from 0.068 to 0.189 h-1. In buccal mucosa COPi was significantly decreased to 7.1 mmHg in rats with venous stasis, whereas Pi and kAlb remained unchanged compared to the sham-operated controls. In hypoproteinemic rats COPGF was 5.0 mmHg and COPp was reduced from 18.9 to 8.0 mmHg. COPi declined from 8.9 mmHg to 2.4 mmHg in gingiva and from 8.1 mmHg to 2.7 mmHg in buccal mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in blood circulation in teeth and supporting tissues incident to experimental tooth movement

Fluorescent microspheres (FM) were used to semi-quantify the effect of orthodontic forces on blood flow in oral tissues in young rats. Forty-five animals had an orthodontic appliance inserted on the first maxillary molar on one side exerting a mesial force of approximately 50 g. Ten animals served as unoperated controls. On days 1, 3, 7, 14, and 21 after the start of the experiment, FM were injected into the left ventricle through an abdominal approach in the experimental and control animals. FM were counted in serial sections from the jaws in the periodontal ligament, pulp, and alveolar bone in a fluorescent microscope. The number of FM per tissue volume and/or tissue weight was taken as a measure of blood flow. The experimental side had significantly lower numbers of FM/mm3 in the periodontal ligament of the first and the second molar on the first day, compared with the contralateral side. However, a steady, significant increase in the number of FM/mm3 in the periodontal and pulpal tissues, and FM/mg in the alveolar bone could be observed on the third and seventh days on the experimental side of the first, second, and third molars compared with the contralateral side, while in the later stages the values of the two sides approached each other. The results of this study indicate that a localized experimental tooth movement initiates a more generalized blood flow response in the periodontal ligament, dental pulp and alveolar bone.

Nerve fibres and cells immunoreactive to neurochemical markers in developing rat molars and supporting tissues

The distribution of nerve fibres immunoreactive to calcitonin gene-related peptide (CGRP), substance P (SP) and neuropeptide Y (NPY) was compared to the general neurochemical markers for nerves and neuroendocrine cells protein gene product 9.5 (PGP 9.5) and neurone-specific enolase (NSE), by use of the avidin-biotin peroxidase complex method in developing dental structures in rats aged 13 to 27 days. A substantially greater part of the nerve fibres was immunoreactive to CGRP and SP than to NPY. In the bell stage, nerve fibres immunoreactive to PGP 9.5, CGRP and SP were found in the dental follicle but not in the dental papilla and stellate reticulum. In the advanced bell stage, after initiation of dentine and enamel formation, PGP 9.5, CGRP- and SP-immunoreactive fibres were found in the dental papilla, while the first NPY-immunoreactive fibres were observed in the papilla when root formation started. Concomitant with the beginning of root development, a subodontoblastic nerve plexus was gradually formed and PGP 9.5-, CGRP- and SP-immunoreactive fibres were found within the dentinal tubules. From the start of root formation, CGRP-, SP- and NPY-immunoreactive nerves were shown in the developing periodontal ligament, although a mature distribution pattern was not observed until root formation was nearly completed. Ameloblasts, odontoblasts and cell-like structures in the outer enamel epithelium and within the dental lamina were PGP 9.5-immunoreactive at the bell stage. As the tooth matured, the immunolabelling gradually decreased, but was still present in some odontoblasts after tooth eruption. NSE-immunoreactive, cell-like structures were found in the periphery of the dental follicle, and persisted close to alveolar bone in the periodontal ligament when the tooth reached occlusion. Hence, it may be concluded that sensory nerves containing SP and CGRP are present in the pulp in advance of sympathetic nerves immunoreactive to NPY.

Effect of electrical tooth stimulation on blood flow, interstitial fluid pressure and substance P and CGRP-immunoreactive nerve fibers in the low compliant cat dental pulp

The effect of vasodilation on simultaneously measured interstitial fluid pressure (IFP, micropuncture) and blood flow (laser-Doppler) in the low compliant pulpal connective tissue was investigated in 10 cats. Vasodilation was induced by electrical stimulation of the tooth after pretreatment with the sympathetic blocker guanethidine. Visualization of the sensory neuropeptides calcitonin gene-related peptide (CGRP) and substance P (SP) was performed using immunocytochemistry. The study was designed to answer the following questions. (1) Does vasodilation promptly increase IFP in low compliant tissues? (2) Does an increase in IFP counteract the blood flow increase? (3) Does repeated electrical stimulation cause reduced staining of CGRP- and SP-immunoreactive nerve fibers in the dental pulp? Electrical stimulation resulted consistently in a nearly synchronous increase in both blood flow and IFP. IFP was nearly doubled, from 6.3 +/- 0.18 mm Hg in control to 11.7 +/- 0.44 mm Hg, whereas blood flow increased by 28%. However, despite continued vasodilation the IFP fell to control level, or even lower, within 1-5 min. The results indicate that the increased IFP will promote fluid absorption into the blood, counteracting a further IFP increase in low compliant tissues during vasodilation. Accordingly, transmural pressure is only transitorily reduced and compression of vessels does not take place. There was considerably less CGRP- and SP-immunoreactive fibers in the stimulated teeth than in the contralateral controls, suggesting that the vasodilation was caused by liberation of these sensory neuropeptides.

Neurogenic inflammation in rat trachea is accompanied by increased negativity of interstitial fluid pressure

The present experiments were performed to investigate whether neurogenic inflammation in rat trachea (with edema formation and protein extravasation when the circulation is intact) induced by electrical field stimulation of neuropeptide-containing C fibers in the vagal nerve is accompanied by increased negativity of interstitial fluid pressure (P(if)). Increased negativity of P(if) in the trachea occurs in dextran anaphylaxis and mast cell degranulation and facilitates edema formation under these circumstances. Experiments were performed after circulatory arrest had been induced in pentobarbital anesthesia to prevent edema formation, which will raise P(if) and potentially cause underestimation of an increased negativity of P(if). After induction of circulatory arrest, the vagal nerve was isolated and placed in a stimulating electrode. The trachea was then exposed and covered with mineral oil, and measurement of P(if) was started as soon as possible thereafter. P(if) was measured with sharpened glass capillaries (tip diameter, 3 to 7 microns) connected to a servocontrolled counterpressure system. P(if) in the control group (n = 12) did not change throughout the observation period. Electrical stimulation of the left vagal nerve caused P(if) to fall in all experiments, from -1.1 +/- 1.1 mm Hg in the control condition to an average of -10.6 +/- 3.4 mm Hg (n = 9, P < .01). In some experiments, a continuous recording of P(if) was obtained, showing that the reduction of P(if) started within 30 seconds after onset of stimulation to reach and later remain at a stable level within a few minutes. The experimental protocol was repeated after the C fibers had been nearly depleted of neuropeptides with capsaicin.(ABSTRACT TRUNCATED AT 250 WORDS)

Nerve fibers immunoreactive to protein gene product 9.5, calcitonin gene-related peptide, substance P, and neuropeptide Y in the dental pulp, periodontal ligament, and gingiva in cats

The distribution patterns of nerve fibers immunoreactive (IR) to calcitonin gene-related peptide (CGRP), substance P (SP), and neuropeptide Y (NPY) in the dental pulp, periodontal ligament (PDL), and gingiva were studied and compared with the complete innervation visualized by antibody to protein gene product (PGP) 9.5 in adult cats. The pulp showed considerably denser nerve supply for PGP 9.5, CGRP, and SP than the periodontal tissues. Most of the pulpal fibers were CGRP-IR, and approximately three to four times more IR fibers were labeled with CGRP than SP. Most fibers in the odontoblast area penetrating into the dentin tubules were CGRP-IR. NPY-IR nerves were mainly observed in connection with the larger blood vessels in pulp and PDL. In the PDL most nerves were localized in the apical third in connection with blood vessels, but CGRP-IR fibers extending close to root cementum were often observed. Immunoreactivity to PGP 9.5 and CGRP was frequently found in cell-like structures in connection with Malassez epithelium in the PDL and in some round epithelial-like cells located in the base of gingival rete pegs.

Increased pressure in venous sinusoids during decongestion of rat nasal mucosa induced by adrenergic agonists

The haemodynamic effects of sympathetic agonists causing decongestion of the nasal mucosa have been investigated in rats. Access to mucosa was obtained from the dorsal side through a small cavity drilled in the nasal bone. The pressures in the venous sinusoids and in the interstitial fluid of nasal mucosa were recorded by micropuncture technique. The local red cell flux (LDF) was monitored by laser Doppler flowmetry, and the blood volume in the mucosa was measured by radio-labelled erythrocytes and albumin. In control rats the tissue blood volume was 0.25 +/- 0.03 g (g wet wt)-1. The interstitial fluid pressure (IFP) was 2.4 +/- 0.6 mmHg and the average blood pressure in venous sinusoids (Ps) was 12.8 +/- 2.7 mmHg. After topical application of noradrenaline (NA) the local blood volume was reduced to 0.12 +/- 0.03 g g-1. Ps was increased to 18.0 +/- 4.0 mmHg, whereas IFP was maintained and LDF was reduced to 40.4% of control, indicating a greater rise in post than in presinusoid vascular resistance. Blocking of both alpha 1 and alpha 2-receptors by phentolamine caused a rise in mucosa blood volume and in LDF by 16 and 20% of control, respectively. Ps increased significantly to 15.2 +/- 3.3 mmHg. Specific stimulation or blocking of alpha 1-receptors by phenylephrine or prazosin induced similar or slightly smaller vascular responses than NA or phentolamine. The effects of the specific alpha 2-agonist (clonidine) or antagonist (yohimbine) on rat mucosa were small, indicating a domination of the alpha 1-receptors. Thus, application of NA caused a rise in blood pressure in the venous sinusoids of nasal mucosa. As LDF fell simultaneously, the reduced blood volume must be due to an increased tone in the muscular wall of venous sinusoids.

Micropuncture measurements of interstitial fluid pressure in normal and inflamed gingiva in rats

Interstitial fluid pressure (IFP) in normal and inflamed gingiva of rats was measured by sharpened glass capillaries (diameter 2-4 microns) connected to a servocontrolled counterpressure system ad modum Wiederhielm. Gingival inflammation was induced by a steel ligature placed unilaterally around the first maxillary molar. After 8 weeks, the ligature was removed and measurements of IFP in normal and experimentally inflamed gingiva were made by puncture through the intact oral epithelium. Average IFP on the control side was 3.5 mm Hg in free, and 7.4 mm Hg in attached gingiva. Compared to the control side, IFP on the experimental inflamed side was elevated significantly (p less than 0.05) both in free and attached gingiva. In the ligated inflamed side IFP in free gingiva averaged 6.7 mm Hg, whereas in attached gingiva it showed a mean value of 10.4 mm Hg. Histological examinations showed a dense infiltrate of inflammatory cells in the connective tissue, while the contralateral control side showed normal features of epithelial and connective tissue. The present finding of increased IFP in the inflamed gingiva may in theory contribute to augmented crevicular fluid flow during inflammation.

Effect of experimental traumatic occlusion on periodontal and pulpal blood flow

Fluorescent microspheres (FM) were used to visualize and semi-quantify flood flow in the periodontal ligament (PDL) and dental pulp during experimental traumatic occlusion of the maxillary and mandibular molar teeth in young rats. At different observation points FM were injected systemically, and the number of FM was counted in serial sections from the jaws in the PDL and pulp of the molar teeth in a fluorescent microscope. Blood flow was related to the number of FM in the tissues and in a reference blood sample. In the early stages an increase in blood flow in the PDL and dental pulp was found on the experimental side compared with the contralateral side. Furthermore, there was an increase in blood flow on both sides of the jaws compared with an unoperated control material. The study thus indicates that a local unilateral occlusal trauma initiates blood flow responses in the total molar dentition in rats.

Effect of traumatic occlusion on CGRP and SP immunoreactive nerve fibre morphology in rat molar pulp and periodontium

Traumatic occlusion provides a trauma that affects the whole tooth and its supporting tissues. To study the effect of this trauma on CGRP and SP immunoreactive nerve morphology in pulp and periodontium, traumatic occlusion was induced in 2-months-old rats. The occlusal surface of the first maxillary molar in 30 rats were unilaterally raised 1 mm with a composite material. At different observation periods up to 30 days, the rats were transcardiacally perfused, the jaws demineralized, sectioned and processed for immunohistochemistry with the avidin-biotin-peroxidase method. Changes in nerve morphology, distribution and density in first and second molars and their supporting tissues were analyzed and compared in experimental (n = 30) and control rats (n = 14). Already after 5 days with traumatic occlusion, 22% of the experimental teeth had increased density of CGRP and SP immunoreactive nerves locally in gingiva, the periodontal ligament and the pulp, while in 15%, axonal proliferation and changed nerve morphology were found in the whole pulp (severe reaction). During a 20-day period, the pulpal nerve reactions progressed and included the whole pulp in 46% of the experimental teeth. The periodontal nerve responses were still localized only to the cervical and apical regions, and they remained local in these areas throughout the experimental periods. After 20 days the number of teeth with severe nerve changes seemed to decrease. The study shows that an unilateral change in occlusion of the first molar initiate nerve responses in the total molar dentition. In this experimental model the pulpal axons containing CGRP and SP reacted more serious to occlusal trauma than the nerves in the periodontium. The results indicate that the nerve changes in some cases might be transient.

Identification of alpha 2 adrenoceptors in the blood vessels of the dental pulp

Using selective agonists and antagonists of alpha2 adrenoceptors, attempts were made to identify the subtype alpha2 adrenoceptors in the blood vessels of the canine dental pulp. In chloralose-anaesthetized dogs, intra-arterial administration of noradrenaline and guanabenz in different doses produced a dose-related pulpal vasoconstriction which was measured using hydrogen-gas clearance. The vasoconstrictor response to noradrenaline was inhibited by phentolamine, a non-selective alpha adrenoceptor antagonist. The response to guanabenz was inhibited by rauwolscine, a highly selective alpha2 adrenoceptor antagonist. The results demonstrated that alpha2 adrenoceptors are present in the blood vessels of dog dental pulp.

Edema-preventing mechanisms in rat gingiva

The long-term effect of increased local venous pressure (Pv) on interstitial fluid pressure (Pi), colloid osmotic pressure (COPi), and fractional removal rate of 125I-labeled human serum albumin (kAlb) was studied in rat gingiva. Measurements were performed on experimental animals and sham-operated controls up to 4 days after ligation of jugular veins. On the day of ligation Pv in the facial veins rose from 2.5 +/- 0.3 (SD) to 15.8 +/- 2.8 mm Hg and stayed at about this level for 2 days before a decrease to 7.4 +/- 0.9 mm Hg on day 4. In free gingiva Pi rose from an average of 3.5 +/- 0.4 to a maximum of 6.3 +/- 0.7 mm Hg, whereas in attached gingiva the corresponding increase in Pi was from 6.0 +/- 0.7 to 11.1 +/- 2.1 mm Hg. One day after the ligation COPi in wick fluid from gingiva was reduced from the control level of 10.6 +/- 1.4 to 4.5 +/- 0.9 mm Hg. COP in plasma and COPi in subcutaneous tissue on the back were unaffected. The removal rate of 125I-labeled albumin (kAlb) from the gingiva showed a nearly threefold increase after venous ligation, from 0.073 +/- 0.01 to 0.211 +/- 0.06 h-1. It is concluded that in free and attached gingiva, both a rise in Pi and a decrease in COPi will counteract the increased filtration pressure and thus prevent edema formation during venous stasis. The fall in COPi is most likely due to increased lymph flow and not dilution, as venous stasis significantly increased kAlb without any visible increase in gingival volume.

Regeneration of calcitonin gene-related peptide immunoreactive nerves in replanted rat molars and their supporting tissues

First maxillary right molars in 66 rats were elevated and replanted and the pulps allowed to regenerate for 1-90 days. The contralateral tooth served as control. Regeneration of nerves in the pulp and periodontium was studied by CGRP-immunohistochemistry and the avidin-biotin-peroxidase method. The pulp and periodontium of the controls were richly supplied with CGRP-labelled nerves. One day after replantation the pulp was completely devoid of CGRP-immunoreactive nerves. After 2 days, axon sprouts were present in the apical, regenerated pulp and in the periodontium. From 3-7 days CGRP-immunoreactive axons were regularly seen to have regenerated in front of the cellular inflammation in the pulp. After 10 days, the pulps were reinnervated up to the horns, although more sparsely than in the controls. From day 20-90 there was a marked divergence in pulpal healing: 17 pulps formed irregular postoperative dentine with a gradual increase in nerve density; 16 pulps remained sparsely innervated and were gradually replaced by bone. Root resorption was most extensive in the teeth with bone replacement of pulp. The soft tissue adjacent to extensive resorbing areas had many more CGRP-labelled axons than in the controls. The reinnervation of the regenerating pulp occurred at the same time as pulpal wound healing, but did not achieve the innervation density of the controls.

Evaluation of pancreatic tissue fluid pressure measurements intraoperatively and by sonographically guided fine-needle puncture

The aim of the present study was to evaluate the needle method for pancreatic tissue fluid pressure measurements. Clinical evaluation was performed in 24 patients with chronic pancreatitis, comparing repeated pressure measurements via sonographically guided fine-needle puncture and intraoperative pressure measurements by direct puncture of pancreatic tissue and duct. In patients with chronic pancreatitis we found small week-to-week variations in sonographically guided percutaneous pressure measurements and good agreement between preoperative percutaneous pressure measurements and intraoperative pressure measurements via direct puncture. Furthermore, no significant difference was seen between pancreatic duct and tissue fluid pressure. The technical evaluation was performed by repeated pressure measurements in human pancreatic autopsy specimens and living rats in a pressure chamber at various external pressure levels. The basic calibration of the method evaluated by means of this pressure chamber study showed sufficient precision and accuracy of the needle technique for clinical and investigative purposes. In conclusion, our results suggest that pancreatic tissue fluid pressure can be reliably assessed by the needle technique.

Effect of portal hypertension and duct ligature on pancreatic fluid pressures in cats

In two groups of cats recordings were performed, during laparotomy, of pancreatic tissue fluid pressure measured by a needle technique, interstitial fluid pressure measured by micropipette technique, pancreatic intraductal pressure, and portal vein pressure. In one group of cats the pressures were measured before and after acutely induced portal hypertension; in the other group of cats the pressures were measured after an overnight ligature of the pancreatic main duct. At rest the needle pressure was equal to duct pressure but significantly lower than interstitial fluid pressure and portal pressure. Acute portal hypertension caused no significant changes in micropipette, needle, or duct pressures. Pancreatic duct ligature increased duct pressure, interstitial fluid pressure, and needle pressure. We conclude that the fluid pressure in the pancreas is probably influenced by the production/drainage relation of the pancreatic juice rather than by haemodynamic conditions.

Cell renewal and ground substance formation in replanted cat teeth

The cellular dynamic pattern of pulpal healing 4, 10, 30, and 60 days after replantation of 47 apicoectomized cat incisors was studied after pulse labeling with 3H-thymidine and 35S-sulfate, autoradiography, and routine histology. In the control teeth the labeling index was less than 0.05%. The apical pulpal cells were capable of ground substance formation and cell proliferation already 4 days after replantation, with a labeling index of 7%, which increased up to 43% within 10 days. A gradual postoperative restitution and reorganization within the pulpal cellular compartment was seen. The maximum cell density, reached after 30 days, was reduced to on average 60% compared with the controls. The tissue reorganization was near completion within all pulpal zones after 60 days, and the labeling index was reduced to 2.5%. In some instances internal resorption in cervical pulpal areas negatively influenced the favorable healing. The present study shows that the pulpal healing in replanted teeth follows a consistent basic pattern in cellular dynamics and in histologic changes. The replanted tooth thus seems to be a suitable model for studies of healing and repair in connective tissues.

Pulpal hemodynamics and interstitial fluid pressure: balance of transmicrovascular fluid transport

The net rate of fluid movement across the microvascular endothelium is governed by hydrostatic and protein osmotic pressures operating on each side of the vessel wall. These basic forces regulating the pulpal transmicrovascular fluid exchange are the same as in other tissues. However, the pulp is special in regard to its enclosement between rigid dentin walls, implying low interstitial compliance. In addition, the pulp has a relatively low perfusion pressure. In the low compliant pulpal interstitium, even a modest rise in net filtration will favor a relatively large increase in interstitial fluid pressure (IFP) which opposes further filtration. This will result in a minimal increase in interstitial fluid volume and, theoretically, any dilution of interstitial protein concentration is not possible. Thus, an increase in vessels' permeability to protein in this low compliant system must be balanced by a further rise in IFP, unless a washout of proteins takes place by raised lymph flow. However, a significant increase in IFP may seriously impede pulpal blood flow both by raising venous vascular resistance and secondarily by reducing pulpal perfusion pressure. The most important edema-preventing mechanisms in tissues with low compliance, as the dental pulp, seems to be a rise in IFP which initiates increased lymph flow and washout of proteins.

Dentin and osteodentin matrix formation in apicoectomized replanted incisors in cats

The reestablishment and rate of osteodentin and dentin matrix formation in 27 apicoectomized replanted and 20 control incisors in cats were studied after Procion H8-BS vital staining. In control teeth the pattern of matrix formation differed in the various pulpal zones, with a higher rate of matrix formed toward apical areas, most dominantly in maxillary incisors. Osteodentin formation could be traced after a lag period of more than 10 days after replantation. Thirty and 60 days postoperatively osteodentin matrix was found in the total pulpal length in 83% and 73% of the teeth, respectively. A common finding was a tubular osteodentin matrix in the pulpal apical third in the replanted teeth. Tubular osteodentin matrix was, however, present most incisally in some teeth 60 days postoperatively. Internal resorption corresponding to outer cervical lesions dominated the pulpal reactions in the maxillary replanted teeth after 60 days. It is concluded that under the present experimental conditions the pulp tissue possesses a high healing potential and that the osteodentin formation reflects the pulpal healing pattern after replantation traumas. The results also indicate that successful pulpal healing depends on unexposed dentinal tubules.

Interlobular arterial resistance: influence of renal arterial pressure and angiotensin II

Pressure in the distal third of the interlobular arteries (Pila) was measured in anesthetized rats by micropuncture through corticotomy. Control Pila was 83.9 (SD 11.9) mm Hg at a renal arterial pressure (RAP) of 113.1 (SD 12.8) mm Hg. Reduction of RAP by 20 mm Hg caused no consistent change of total renal blood flow (RBF) or Pila. Relative interlobular arterial resistance, Rila = (RAP - Pila)/RBF, fell by 40 to 50%, and then remained practically unchanged at further reduction of RAP. Blood flow measured by radiolabeled microspheres (10.7 micron) showed similar values in intact cortex and in the tissue beneath the corticotomy, both varying in proportion to RBF. Intravenous infusion of angiotensin II (AII) 40 to 90 ng/min reduced RBF by 29% and increased RAP by 19 mm Hg. Pila rose by only 8 mm Hg and Rila increased to 209% of control. Reduction of RAP to control level during continued AII infusion did not change RBF, while Rila fell to 131% of control. We conclude that: dilatation and constriction of the interlobular arteries contribute importantly to autoregulation of outer cortical blood flow, probably through a myogenic mechanism (Bayliss); the constriction of interlobular arteries elicited by i.v. AII reflects mainly an autoregulatory response to increased arterial pressure, and to a smaller extent, a direct constrictor effect of AII.

Autoregulation of renal blood flow in two-kidney, one-clip hypertensive rats

Renal blood flow (RBF) autoregulation was examined in the clipped and nonclipped kidneys in two groups of two-kidney, one-clip (2K-1C) hypertensive rats 10 wk after clipping. The arterial pressure distal to the clip and the renin secretion rate (RSR) were also examined. The blood pressure (BP) was 149 +/- 4 and 162 +/- 6 mmHg in the two hypertensive groups vs. 114 +/- 3 mmHg in the controls (P less than 0.02). The RBF (in ml X min-1 X kidney-1) was 4.27 +/- 0.41 in the nonclipped and 2.18 +/- 0.23 in the clipped kidneys (P less than 0.001). The pressure distal to the clip was 104 +/- 7 mmHg. The renal vascular resistance (RVR) (in mmHg X ml-1 X min-1 X g-1) was 25.0 +/- 1.4 in the control kidneys vs. 58.4 +/- 4.5 in the nonclipped (P less than 0.001) and 39.9 +/- 6.6 in the clipped kidneys (P less than 0.01). The RBF autoregulation was well preserved in the nonclipped kidneys but reset to a higher lower pressure limit of autoregulation of 106 +/- 4 mmHg, which was significantly higher than in the normotensive controls (84 +/- 6 mmHg) (P less than 0.01). In the clipped kidneys there was complete loss of RBF autoregulation. RSR decreased with reduction of the perfusion pressure in the clipped kidneys. The increased RVR might have been due to a combination of structural and functional changes in both kidneys.

Pulpal blood flow in immature permanent dog teeth after replantation

Pulpal blood flow (PBF) was measuring by H2-gas clearance in 35 replanted (incisors and premolars) and 22 contralateral control dog teeth. The PBF measurements were taken 6, 10, 16, 21 and 28 days after replantation. At 6, 10 and 16 days after replantation there was no measurable blood flow in the coronal pulp of either replanted incisors or premolars. 21 days after replantation a considerable reduction in PBF was measured in all replanted teeth. On average, PBF was reduced to about one fifth of PBF in the simultaneously measured contralateral controls. Four weeks after replantation, a more than threefold increase in PBF was measured in premolars with two roots, while PBF in premolars with one root and incisors was consistently reduced to an average of 40% of the controls. The vascular pattern of the teeth 4 wk after replantation was identified with perfusion of silicon rubber. The measurements suggest that replanted multirooted teeth revascularize more easily than single-rooted teeth, and that pulpal repair is restored by a gradual replacement and proliferation of new tissue.