Mechanisms mediating nitroglycerin-induced delayed-onset hyperalgesia in the rat.

Nitroglycerin (glycerol trinitrate, GTN) induces headache in migraineurs, an effect that has been used both diagnostically and in the study of the pathophysiology of this neurovascular pain syndrome. An important feature of this headache is a delay from the administration of GTN to headache onset that, because of GTN's very rapid metabolism, cannot be due to its pharmacokinetic profile. It has recently been suggested that activation of perivascular mast cells, which has been implicated in the pathophysiology of migraine, may contribute to this delay. We reported that hyperalgesia induced by intradermal GTN has a delay to onset of ∼ 30 min in male and ∼ 45 min in female rats. This hyperalgesia was greater in females, was prevented by pretreatment with the anti-migraine drug, sumatriptan, as well as by chronic pretreatment with the mast cell degranulator, compound 48/80. The acute administration of GTN and compound 48/80 both induced hyperalgesia that was prevented by pretreatment with octoxynol-9, which attenuates endothelial function, suggesting that GTN and mast cell-mediated hyperalgesia are endothelial cell-dependent. Furthermore, A-317491, a P2X3 antagonist, which inhibits endothelial cell-dependent hyperalgesia, also prevents GTN and mast cell-mediated hyperalgesia. We conclude that delayed-onset mechanical hyperalgesia induced by GTN is mediated by activation of mast cells, which in turn release mediators that stimulate endothelial cells to release ATP, to act on P2X3, a ligand-gated ion channel, in perivascular nociceptors. A role of the mast and endothelial cell in GTN-induced hyperalgesia suggests potential novel risk factors and targets for the treatment of migraine.

Homocysteine-induced attenuation of vascular endothelium-dependent hyperalgesia in the rat.

We have recently demonstrated a role of the vascular endothelium in peripheral pain mechanism by disrupting endothelial cell function using intravascular administration of octoxynol-9, a non-selective membrane active agent. As an independent test of the role of endothelial cells in pain mechanisms, we evaluated the effect of homocysteine, an agent that damages endothelial cell function. Mechanical stimulus-induced enhancement of endothelin-1 hyperalgesia in the gastrocnemius muscle of the rat was first prevented then enhanced by intravenous administration of homocysteine, but was only inhibited by its precursor, methionine. Both homocysteine and methionine significantly attenuated mechanical hyperalgesia in two models of ergonomic muscle pain, induced by exposure to vibration, and by eccentric exercise, and cutaneous mechanical hyperalgesia in an ischemia-reperfusion injury model of Complex Regional Pain Syndrome type I, all previously shown responsive to octoxynol-9. This study provides independent support for a role of the endothelial cell in pain syndromes thought to have a vascular basis, and suggests that substances that are endothelial cell toxins can enhance vascular pain.

NOP receptor mediates anti-analgesia induced by agonist-antagonist opioids.

Clinical studies have shown that agonist-antagonist opioid analgesics that produce their analgesic effect via action on the kappa-opioid receptor, produce a delayed-onset anti-analgesia in men but not women, an effect blocked by co-administration of a low dose of naloxone. We now report the same time-dependent anti-analgesia and its underlying mechanism in an animal model. Using the Randall-Selitto paw-withdrawal assay in male rats, we found that nalbuphine, pentazocine, and butorphanol each produced analgesia during the first hour followed by anti-analgesia starting at ∼90min after administration in males but not females, closely mimicking its clinical effects. As observed in humans, co-administration of nalbuphine with naloxone in a dose ratio of 12.5:1 blocked anti-analgesia but not analgesia. Administration of the highly selective kappa-opioid receptor agonist U69593 produced analgesia without subsequent anti-analgesia, and confirmed by the failure of the selective kappa antagonist nor-binaltorphimine to block nalbuphine-induced anti-analgesia, indicating that anti-analgesia is not mediated by kappa-opioid receptors. We therefore tested the role of other receptors in nalbuphine anti-analgesia. Nociceptin/orphanin FQ (NOP) and sigma-1 and sigma-2 receptors were chosen on the basis of their known anti-analgesic effects and receptor binding studies. The selective NOP receptor antagonists, JTC801, and J-113397, but not the sigma receptor antagonist, BD 1047, antagonized nalbuphine anti-analgesia. Furthermore, the NOP receptor agonist NNC 63-0532 produced anti-analgesia with the same delay in onset observed with the three agonist-antagonists, but without producing preceding analgesia and this anti-analgesia was also blocked by naloxone. These results strongly support the suggestion that clinically used agonist-antagonists act at the NOP receptor to produce anti-analgesia.

Ectopic uterine tissue as a chronic pain generator.

While chronic pain is a main symptom in endometriosis, the underlying mechanisms and effective therapy remain elusive. We developed an animal model enabling the exploration of ectopic endometrium as a source of endometriosis pain. Rats were surgically implanted with autologous uterus in the gastrocnemius muscle. Within two weeks, visual inspection revealed the presence of a reddish-brown fluid-filled cystic structure at the implant site. Histology demonstrated cystic glandular structures with stromal invasion of the muscle. Immunohistochemical studies of these lesions revealed the presence of markers for nociceptor nerve fibers and neuronal sprouting. Fourteen days after surgery rats exhibited persistent mechanical hyperalgesia at the site of the ectopic endometrial lesion. Intralesional, but not contralateral, injection of progesterone was dose-dependently antihyperalgesic. Systemic administration of leuprolide also produced antihyperalgesia. In vivo electrophysiological recordings from sensory neurons innervating the lesion revealed a significant increase in their response to sustained mechanical stimulation. These results are consistent with clinical and pathological findings observed in patients with endometriosis, compatible with the ectopic endometrium as a source of pain. This model of endometriosis allows mechanistic exploration at the lesion site facilitating our understanding of endometriosis pain.

Stress enhances muscle nociceptor activity in the rat.

Chronic widespread pain, such as observed in irritable bowel (IBS) and fibromyalgia (FMS) syndrome, are markedly affected by stress. While such forms of stress-induced hyperalgesia are generally considered manifestations of "central sensitization," recent studies in patients with IBS and FMS suggest an additional, peripheral contribution. To examine the effect of stress on muscle nociceptor function, we evaluated activity in nociceptors innervating the gastrocnemius muscle in an animal model of chronic widespread pain, water avoidance stress, in the rat. This stressor, which produces mechanical hyperalgesia in skeletal muscle produced a significant decrease (∼34%) in mechanical threshold of muscle nociceptors and a marked, ∼two-fold increase in the number of action potentials produced by a prolonged (60 s) fixed intensity suprathreshold 10 g stimulus. Stress also induced an increase in conduction velocity from 1.25 m/s to 2.09 m/s, and increased variability in neuronal activity. Given that these changes, each of at least moderate magnitude, would be expected to enhance nociceptor activity, it is likely that, taken together, they contribute to the enhanced nociception observed in this model of stress-induced chronic widespread pain.

Healthcare issues of detainees in police custody in London, UK.

Little is known about the general healthcare needs of detainees in police custody. The aims of this study were to: determine the level of general health issues, diseases and/or pathology for detainees in police custody, and to determine how well those general health issues, diseases and/or pathology are being managed. This was done by a detailed analysis of healthcare issues of a cohort of detainees and reviewing intended and prescribed medication needs with current medication availability. In August 2007, a prospective detailed, anonymised, structured questionnaire survey was undertaken of 201 detainees in police custody in London, UK. Of these 83.6% consented to participate in the study. 85.1% of subjects were male; mean age was 33.9 years; 70.8% had English as a first language; 13.7% were of no fixed abode; 70.2% were registered with a general practitioner (primary care physician); 25% were already in contact with other healthcare teams; 7.1% had previously been sectioned under the Mental Health Act 1983; 16.7% had previously intentionally self-injured; 33.9% were dependent on heroin, 33.9% on crack cocaine; 25% on alcohol, 16.6% on benzodiazepines and 63.1% on cigarettes. 56% of subjects had active medical conditions; of those with active medical conditions 74% were prescribed medication for those medical conditions; only 3/70 had their medication available. 28/70 were not taking medication regularly, and many were not taking it at all. Three subjects who had deep vein thromboses were not taking their prescribed anticoagulants and six subjects with severe mental health issues were not taking their anti-psychotic medication. Mental health issues and depression predominated, but there was a very large range of mixed diseases and pathology. Asthma, epilepsy, diabetes, deep vein thrombosis, pulmonary embolism, hepatitis, and hypertension were all represented. The study has achieved its aims and has also shown that--in part because of the chaotic lifestyle of many detainees--appropriate care was not being rendered, thereby, putting both detainee, and potentially others coming into contact with them, at risk.

Provision of forensic medical services to police custody suites in England and Wales: current practice.

INTRODUCTION: Police services within England and Wales are required under the Police and Criminal Evidence Act 1984 to ensure appropriate healthcare to those detained in police custody (forensic medical services). Traditionally doctors have been used by police services to provide an appropriate level of care. Changes within the Act allowed other healthcare professionals (nurses and paramedics and emergency care practitioners) to be included in the provision of such services. The aim of this appears at least in part to have been to reduce the costs of providing such a service. In recent years police services within England and Wales have been outsourced to assorted commercial providers. There are now several different modes of delivery of forensic medical services, which are determined locally by separate police services. AIMS: This study aimed (a) to determine the different modes of delivery of forensic medical services in England and Wales; (b) to determine the healthcare workload caused by Police and Criminal Evidence Act 1984 Codes of Practice; (c) to determine the relative costs of different service models and (d) to determine availability of such information from the police services. METHODS: The study was undertaken in two parts--(a) a telephone survey of all police services, and (b) an application to each police service utilising the Freedom of Information Act 2000. RESULTS: All police services (n=43) in England and Wales were contacted. Of the 41 forces that furnished detailed information; 13/41 had a doctor only service; 20/41 had a doctor/nurse service; 6/41 had a doctor/nurse/paramedic service; 1/41 had a doctor/emergency care practitioner service (who may be nurses or paramedic); 1/41 had a doctor/paramedic service. 23/43 services were outsourced to private commercial providers. Mean cost per patient contact (in 17/43 services which supplied data) was GBP 97.25. The cheapest cost per patient contact was the Metropolitan Police Service - a doctor only service (GBP 56.4), the highest Lincolnshire--a doctor only service (GBP 151.1). Mean cost for a doctor only service was GBP 97.1; for a doctor/nurse service--GBP 91.56 and for a doctor/nurse/paramedic service--GBP 115.76. There was no significant difference in costs per patient contact between a doctor only versus mixed HCP delivery of service. Relative costs and 95% confidence intervals expressed as a percentage show that a doctor only model was on average 3.4% lower than a mixed HCP provision, and that a non-outsourced service was on average 9.9% less than an outsourced service. No outsourced service in this study uses a doctor only model. CONCLUSIONS: The study shows that there was a complete lack of consistency in the recording and availability of information regarding forensic medical services for police services in England and Wales. The information that was obtained suggested that usage of such services varied greatly between police services and that costs of forensic medical services appear to be increased by the use of mixed healthcare professional service delivery and by using external commercial providers.

Role of interleukin-6 in chronic muscle hyperalgesic priming.

After recovery from acute muscle pain even minor subsequent muscle use can initiate recurrence of the same mechanical hyperalgesia months or years after the initial injury. We have recently developed a model of this chronic latent hyperalgesia in the rat. In this study, we have examined the possibility that interleukin-6 (IL-6), an inflammatory mediator produced during acute muscle inflammation, can mediate the production of this chronic latent hyperalgesic state in which subsequent exposure to inflammatory mediators produces a markedly prolonged mechanical hyperalgesia. We now report that i.m. injection of IL-6 produced mechanical hyperalgesia, lasting several hours, that was prevented by intrathecal injection of antisense to glycoprotein 130 (gp130), an IL-6 receptor subunit. Furthermore, following complete recovery from i.m. IL-6-induced hyperalgesia, i.m. prostaglandin E(2) produced a mechanical hyperalgesia that was remarkably prolonged compared with naïve controls, indicating the presence of chronic latent hyperalgesia. This ability of IL-6 to produce chronic latent hyperalgesia was prevented by intrathecal administration of antisense for gp130. Furthermore, gp130 antisense also prevented chronic latent hyperalgesia produced by i.m. injection of the inflammogen, carrageenan. These results identify a role for IL-6 in acute inflammatory muscle pain and as a potential target against which therapies might be directed to treat chronic muscle pain.

Relationships between sediment microbial communities and pollutants in two California salt marshes.

Salt marshes are important ecosystems whose plant and microbial communities can alter terrestrially derived pollutants prior to coastal water discharge. However, knowledge regarding relationships between anthropogenic pollutant levels and salt marsh microbial communities is limited, and salt marshes on the West Coast of the United States are rarely examined. In this study, we investigated the relationships between microbial community composition and 24 pollutants (20 metals and 4 organics) in two California salt marshes. Multivariate ordination techniques were used to assess how bacterial community composition, as determined by terminal restriction fragment length polymorphism and phospholipid fatty acid analyses, was related to pollution. Sea urchin embryo toxicity measurements and plant tissue metabolite profiles were considered two other biometrics of pollution. Spatial effects were strongly manifested across marshes and across channel elevations within marshes. Utilizing partial canonical correspondence analysis, an ordination technique new to microbial ecology, we found that several metals were strongly associated with microbial community composition after accounting for spatial effects. The major patterns in plant metabolite profiles were consistent with patterns across microbial community profiles, but sea urchin embryo assays, which are commonly used to evaluate ecological toxicity, had no identifiable relationships with pollution. Whereas salt marshes are generally dynamic and complex habitats, microbial communities in these marshes appear to be relatively sensitive indicators of toxic pollutants.

Upgrading of existing sludge treatment processes for phosphorus management serving a EBPR WWTP.

For a large-scale wastewater treatment plant to comply with phosphorus consents using enhanced biological phosphorus removal processes, its sludge and liquor treatment processes need to be carefully upgraded. In this case study, the wastewater treatment plant of interest has three different types of sludge treated by two different and independent sludge treatment processes. The task of upgrading the sludge treatment systems to serve an EBPR process while satisfying other regulatory and operational constraints in a cost effective way presents an interesting challenge. A range of process options was investigated to include P-rich surplus activated sludge treatment, raw sludge treatment, and sludge liquors treatment. Sludge pre-liming, i.e. to introduce lime slurry into raw liquid sludge before the dewatering stage, was studied in bench-scale and full-scale trials for phosphorus precipitation and pathogen reduction. It was applied to the mixture of surplus activated sludge and imported sludge. The results showed that a complete phosphorus precipitation was achieved at above pH 9 with lime addition of 7% (w/w as calcium hydroxide to sludge dry weight). A satisfactory 2-log pathogen reduction was consistently achieved at above pH 11 with lime addition of 14% (w/w). The process significantly simplified the potential upgrading work for sludge and liquor treatment, compared to other alternatives.

Key influential factors for sludge pre-fermentation process design--a case study.

Sewage sludge pre-fermentation process produces readily biodegradable carbon, which is essential for reliable biological phosphorus removal and efficient denitrification. This bench scale study was to develop site-specific design parameters for a sludge fermentation process, and to look into the effects of various influential factors. The key factors investigated induded solids retention time (4-8 days), temperature (9-19 degrees C) and sludge concentrations (0.5%-4% DS). The optimum Volatile Fatty Adds yield was found at a sludge concentration of 1%-1.5% DS. A solid retention time of 4 days at 15-20 degrees C was found to be most cost effective. The fermentation reaction was temperature sensitive, which was found to be inefficient at temperature below 12-15 degrees C. Under the optimum conditions, 80-100 mgVFA g(-1) VSS can be generated from fermentation process, which will result in an increase of 20-24 mg l(-1) in the settled sewage based on average flow. A significant pathogen reduction level was also demonstrated over the fermentation period. Liquid sludge from the small rural wastewater treatment plants is often imported to a regional sludge treatment centre for more advanced treatment to comply with the Regulations. The suitability of this imported sludge for pre-fermentation process was also investigated in this study.

Central terminals of nociceptors are targets for nicotine suppression of inflammation.

Spinal intrathecal administration of nicotine inhibits bradykinin-induced plasma extravasation, a component of the inflammatory response, in the knee joint of the rat in a dose-related fashion. Nociceptors contain nicotinic receptors and activation of a nociceptor at its peripheral terminal, by capsaicin, also produces inhibition of inflammation. Therefore the aim of this study was to test the hypothesis that the spinal target for this effect of nicotine is the central terminal of the primary afferent nociceptor. Intrathecal administration of the neurokinin-1 receptor antagonist, (3aR,7aR)-7,7-diphenyl-2-(1-imino-2(2-methoxyphenyl)-ethyl) perhydroisoindol-4-1 hydrochloride or the N-methyl-D-aspartate receptor antagonist, DL-2-amino-5-phosphonovaleric acid, both antagonists of the action of primary afferent neurotransmitters, markedly attenuated the inhibition of bradykinin-induced plasma extravasation produced by both intrathecal nicotine and intraplantar capsaicin.Conversely, intrathecal administration of an alpha-adrenoceptor antagonist, phentolamine or an opioid receptor antagonist, naloxone, to block descending antinociceptive controls, which provide inhibitory input to primary afferent nociceptors, enhanced the action of both nicotine and capsaicin. These findings support the hypothesis that the central terminal of the primary afferent nociceptor is a CNS target at which nicotine acts to inhibit inflammation.

Fasting is a physiological stimulus of vagus-mediated enhancement of nociception in the female rat.

The vagus nerve modulates nociception by a mechanism dependent upon gonadal hormones and the adrenal medulla. In the present study we tested the hypothesis that this modulation is dynamically controlled by physiological stimulation of structures innervated by the subdiaphragmatic vagus. Specifically, food deprivation (fasting) was employed to increase activity in the subdiaphragmatic vagus, and the experiments were performed mainly in female rats because our previous observations suggested that baseline activity in the pathway is lower in females than in males. Consistent with the hypothesis, after a 48-h fast, female rats exhibited increased nociceptive behavior in the formalin test. In contrast, fasting had no effect on formalin-evoked nociceptive behavior in male rats. The fasting-induced effect on nociception appears to be mediated by the vagus nerve since it is prevented by subdiaphragmatic vagotomy. Also similar to the previously characterized vagus-mediated modulation, the effect of fasting in the female is blocked by gonadectomy or adrenal medullectomy, and hormone replacement with 17beta-estradiol in gonadectomized female rats restored the effect of fasting. Decreased glucose metabolism apparently does not play a significant role in the effect of fasting on nociception, since the effect was unchanged when 5% glucose was provided in the drinking water throughout the fasting period. On the other hand, increasing the bulk content of the stomach (without providing nutrients) by infusion of petrolatum significantly attenuated the effect of fasting during the interphase period of the formalin response, suggesting that decreased gut distention, and possibly motility, are important in fasting-induced enhancement of nociception. These results indicate that fasting is a physiological activator of the vagus-mediated pain modulation pathway. This suggests the possibility that, especially in females, natural periodic changes in gut distention and motility may control an ongoing vagus-mediated adjustment in the organism's nociceptive sensitivity.

Role of adrenal medulla in development of sexual dimorphism in inflammation.

Many inflammatory diseases show a female predilection in adults, but not prepubertally. Because sex differences in the inflammatory response in the adult rat are mediated, in part, by sexual dimorphism in adrenal medullary function, we investigated the contribution of the adrenal medulla to the ontogeny of sexual dimorphism in inflammation. Whilst there was no sex difference in the magnitude of the plasma extravasation (PE) induced by the potent inflammatory mediator bradykinin (BK) in prepubertal rats, in adult rats BK-induced PE was markedly greater in males. Also, adult male rats, gonadectomized prior to puberty, had a lower magnitude of BK-induced PE than did adult male controls, whilst adult females gonadectomized prepubertally had higher BK-induced PE than did controls. In rats gonadectomized after puberty, the magnitude of BK-induced PE in adult males was not affected, whilst in females it resulted in significantly higher BK-induced PE, similar to the effect of prepubertal gonadectomy. When tested prepubertally, adrenal denervation increased the magnitude of BK-induced PE in females, but not in males. In contrast, in both males and females tested as adults, but castrated prepubertally, and in gonad-intact adult females, adrenal denervation significantly increased the magnitude of BK-induced PE. Adrenal denervation in prepubertal females given adult levels of 17beta-oestradiol produced a marked enhancement in the denervation-induced increase in magnitude of BK-induced PE compared to females not exposed prematurely to sex hormones. These studies suggest that an adrenal medulla-dependent inhibition of BK-induced PE is present in female but not male rats, and is enhanced by oestrogen but suppressed by testosterone.

Gender and gonadal hormone effects on vagal modulation of tonic nociception.

We studied the influence of gender and gonadal hormones on modulation of tonic nociception exerted by vagal activity. In male rats, subdiaphragmatic vagotomy resulted in significantly reduced nociceptive behavior during phase 2 of the formalin test. Whereas gonadectomy alone had no effect, it completely eliminated the suppressive effect of subdiaphragmatic vagotomy; however, sex hormone replacement with either testosterone or dihydrotestosterone did not restore the ability of subdiaphragmatic vagotomy to suppress nociceptive behavior. These results suggest that, in males, a gonad-dependent but androgenic gonadal hormone-independent mechanism contributes to pronociceptive effects of vagal afferent activity. Although neither gonadectomy nor subdiaphragmatic vagotomy alone affected the response to formalin in females, gonadectomy plus vagotomy resulted in significantly reduced nociceptive behavior during phase 2. Reconstitution with 17 beta-estradiol implants in gonadectomized females not only prevented suppression of nociceptive behavior seen with gonadectomy plus vagotomy, but also led to increased nociceptive behavior in the interphase between phases 1 and 2. However, placement of 17 beta-estradiol implants in gonad-intact females had no effect on formalin-induced nociceptive behavior. The finding that estrogen produced an increase in nociceptive behavior in gonadectomized female rats after vagotomy but not in normal female rats (with intact gonads and subdiaphragmatic vagus) suggests that the interaction between estrogen and nociceptive afferent activity is suppressed by vagal function. In conclusion, a nonandrogenic action of testicular function in male rats and estrogen in females seems to influence the effect of vagal activity on formalin-induced nociceptive behavior.

Opioid inhibition of formalin-induced changes in plasma extravasation and local blood flow in rats.

Hindpaw injection of dilute formalin produces brief (Phase 1) and persistent (Phase 2) nociceptive responses in the rat. We recently showed that systemically-administered remifentanil during Phase 1 interacted with peripheral opioid receptors to delay the onset and termination of Phase 2 (Taylor et al., 1997b). To test the hypothesis that opioid inhibition of proinflammatory events during Phase 1 contributed to this delay, we evaluated the effects of remifentanil on the time course of formalin-induced inflammation. We found that formalin increased paw thickness (edema), plasma extravasation and local blood flow within minutes of its injection, i.e. during Phase 1. Each of these responses was blocked during remifentanil administration (30 microg/kg i.v. bolus, followed 90 s later with a 15 microg/kg/min infusion for 13.5 min), indicating that opioids inhibit Phase 1 inflammation. Opioid blockade of the blood flow response could be reversed with a peripherally-acting opioid antagonist, naloxone methiodide, indicating that remifentanil acted upon peripheral opioid receptors. Although the administration of remifentanil during Phase 1 did not reduce the magnitude of inflammatory responses during Phase 2, it did delay the onset and termination of edema during Phase 2. As this corresponds to the effects of remifentanil on nociceptive responses during Phase 2, we suggest that opioid analgesics act upon peripheral sites to inhibit inflammation during Phase 1, leading to a delay in the temporal profile of inflammatory (and likely nociceptive) responses during Phase 2.

Painful stimulation suppresses joint inflammation by inducing shedding of L-selectin from neutrophils.

Although the inflammatory response is essential for protecting tissues from injury and infection, unrestrained inflammation can cause chronic inflammatory diseases such as arthritis, colitis and asthma. Physiological mechanisms that downregulate inflammation are poorly understood. Potent control might be achieved by regulating early stages in the inflammatory response, such as accumulation of neutrophils at the site of injury, where these cells release chemical mediators that promote inflammatory processes including plasma extravasation, bacteriocide and proteolysis. To access an inflammatory site, neutrophils must first adhere to the vascular endothelium in a process mediated in part by the leukocyte adhesion molecule L-selectin. This adhesion is prevented when L-selectin is shed from the neutrophil membrane. Although shedding of L-selectin is recognized as a potentially important mechanism for regulating neutrophils, its physiological function has not been demonstrated. Shedding of L-selectin may mediate endogenous downregulation of inflammation by limiting neutrophil accumulation at inflammatory sites. Here we show that activation of nociceptive neurons induces shedding of L-selectin from circulating neutrophils in vivo and that this shedding suppresses an ongoing inflammatory response by inhibiting neutrophil accumulation. These findings indicate a previously unknown mechanism for endogenous feedback control of inflammation. Failure of this mechanism could contribute to the etiology of chronic inflammatory disease.

Sex steroid regulation of the inflammatory response: sympathoadrenal dependence in the female rat.

To investigate the role of sex steroids in sex differences in the response of rats to the potent inflammatory mediator bradykinin (BK), we evaluated the effect of sex steroid manipulation on the magnitude of BK-induced synovial plasma extravasation (PE). The magnitude of BK-induced PE is markedly less in females. Ovariectomy of female rats increased BK-induced PE, and administration of 17beta-estradiol to ovariectomized female rats reconstituted the female phenotype. Castration in male rats decreased BK-induced PE, and administration of testosterone or its nonmetabolizable analog dihydrotestosterone reconstituted the male phenotype. The results of these experiments strongly support the role of both male and female sex steroids in sex differences in the inflammatory response. Because the stress axes are sexually dimorphic and are important in the regulation of the inflammatory response, we evaluated the contribution of the hypothalamic-pituitary-adrenal and the sympathoadrenal axes to sex differences in BK-induced PE. Neither hypophysectomy nor inhibition of corticosteroid synthesis affected BK-induced PE in female or male rats. Adrenal denervation in females produced the same magnitude increase in BK-induced PE as adrenalectomy or ovariectomy, suggesting that the adrenal medullary factor(s) in females may account for the female sex steroid effect on BK-induced PE. Furthermore, we have demonstrated that in female but not male rats, estrogen receptor alpha immunoreactivity is present on medullary but not cortical cells in the adrenal gland. These data suggest that regulation of the inflammatory response by female sex steroids is strongly dependent on the sympathoadrenal axis, possibly by its action on estrogen receptors on adrenal medullary cells.

Bradykinin-induced neurogenic migration of neutrophils into the rat knee joint.

This study examined the dependence of neurogenic and non-neurogenic synovial plasma extravasation on neutrophils. Perfusion of bradykinin into the knee joint produced both a rapid increase in the magnitude of plasma extravasation and a significant increase in number of neutrophils in the synovium. Both bradykinin-induced plasma extravasation and neutrophil accumulation were dependent on sympathetic post-ganglionic neuron terminals, since both were blocked in sympathectomized rats. Platelet activating factor, which produces plasma extravasation independent of sympathetic neurons, did not increase the number of neutrophils in the synovium. These findings support the suggestion that bradykinin acts on sympathetic nerve terminals in the knee leading to attraction of neutrophils, which promotes plasma extravasation.