Preclinical characterisation of the GM-CSF receptor as a therapeutic target in rheumatoid arthritis

Objective

Previous work has suggested that the granulocyte macrophage colony stimulating factor (GM-CSF)–GM-CSF receptor α axis (GM-CSFRα) may provide a new therapeutic target for the treatment of rheumatoid arthritis (RA). Therefore, we investigated the cellular expression of GM-CSFRα in RA synovial tissue and investigated the effects of anti-GM-CSFRα antibody treatment in vitro and in vivo in a preclinical model of RA.

Methods

We compared GM-CSFRα expression on macrophages positive for CD68 or CD163 on synovial biopsy samples from patients with RA or psoriatic arthritis (PsA) to disease controls. In addition, we studied the effects of CAM-3003, an anti-GM-CSFR antibody in a collagen induced arthritis model of RA in DBA/1 mice. The pharmacokinetic profile of CAM-3003 was studied in naïve CD1(ICR) mice (see online supplement) and used to interpret the results of the pharmacodynamic studies in BALB/c mice.

Results

GM-CSFRα was expressed by CD68 positive and CD163 positive macrophages in the synovium, and there was a significant increase in GM-CSFRα positive cells in patients in patients with RA as well as patients with PsA compared with patients with osteoarthritis and healthy controls. In the collagen induced arthritis model there was a dose dependent reduction of clinical arthritis scores and the number of F4/80 positive macrophages in the inflamed synovium after CAM-3003 treatment. In BALB/c mice CAM-3003 inhibited recombinant GM-CSF mediated margination of peripheral blood monocytes and neutrophils.

Conclusions

The findings support the ongoing development of therapies aimed at interfering with GM-CSF or its receptor in various forms of arthritis, such as RA and PsA.

Dectin-2 sensing of house dust mite is critical for the initiation of airway inflammation

How the immune system senses aeroallergens and triggers an aberrant inflammation is poorly understood. Dectin-2 is a house dust mite (HDM)-sensing pattern recognition receptor. In a 3-week mouse model of repeated intranasal HDM challenge, anti-Dectin-2 potently attenuated the characteristic allergic inflammation and airway hyper-responsiveness. Anti-Dectin-2 also prevented neutrophil influx following a single HDM challenge. Interestingly, cysteinyl leukotrienes, but not chemokine and cytokine levels were inhibited by anti-Dectin-2 in this acute model, and in ex vivo challenge of cultured alveolar macrophages with HDM. Furthermore in the single-challenge model, zileuton, an inhibitor of leukotriene production, produced a similar effect as Dectin-2 blockade. Together these data suggest alveolar macrophage sensing of HDM by Dectin-2 elicits the production of cysteinyl leukotrienes, and this axis is key for the initiation of airway inflammation to this aeroallergen. Finally, we found Dectin-2-positive infiltrating cells present in bronchial biopsies from asthmatic subjects.

A novel IgE-neutralizing antibody for the treatment of severe uncontrolled asthma

The critical role played by IgE in allergic asthma is well-documented and clinically precedented, but some patients in whom IgE neutralization may still offer clinical benefit are excluded from treatment with the existing anti-IgE therapy, omalizumab, due to high total IgE levels or body mass. In this study, we sought to generate a novel high affinity anti-IgE antibody (MEDI4212) with potential to treat a broad severe asthma patient population. Analysis of body mass, total and allergen-specific IgE levels in a cohort of severe asthmatics was used to support the rationale for development of a high affinity IgE-targeted antibody therapeutic. Phage display technology was used to generate a human IgG1 lead antibody, MEDI4212, which was characterized in vitro using binding, signaling and functional assay systems. Protein crystallography was used to determine the details of the interaction between MEDI4212 and IgE. MEDI4212 bound human IgE with an affinity of 1.95 pM and was shown to target critical residues in the IgE Cε3 domain critical for interaction with FcεRI. MEDI4212 potently inhibited responses through FcεRI and also prevented the binding of IgE to CD23. When used ex vivo at identical concentration, MEDI4212 depleted free-IgE from human sera to levels ~1 log lower than omalizumab. Our results thus indicate that MEDI4212 is a novel, high affinity antibody that binds specifically to IgE and prevents IgE binding to its receptors. MEDI4212 effectively depleted free-IgE from human sera ex vivo to a level (1 IU/mL) anticipated to provide optimal IgE suppression in severe asthma patients.

Protein engineering and preclinical development of a GM-CSF receptor antibody for the treatment of rheumatoid arthritis

BACKGROUND AND PURPOSE

For antibody therapies against receptor targets, in vivo outcomes can be difficult to predict because of target-mediated clearance or antigen 'sink' effects. The purpose of this work was to engineer an antibody to the GM-CSF receptor α (GM-CSFRα) with pharmacological properties optimized for chronic, s.c. treatment of rheumatoid arthritis (RA) patients.

EXPERIMENTAL APPROACH

We used an in silico model of receptor occupancy to guide the target affinity and a combinatorial phage display approach for affinity maturation. Mechanism of action and internalization assays were performed on the optimized antibody in vitro before refining the modelling predictions of the eventual dosing in man. Finally, in vivo pharmacology studies in cynomolgus monkeys were carried out to inform the predictions and support future clinical development.

KEY RESULTS

Antibody potency was improved 8600-fold, and the target affinity was reached. The refined model predicted pharmacodynamic effects at doses as low as 1 mg kg(-1) and a study in cynomolgus monkeys confirmed in vivo efficacy at 1 mg kg(-1) dosing.

CONCLUSIONS AND IMPLICATIONS

This rational approach to antibody drug discovery enabled the isolation of a potent molecule compatible with chronic, s.c. self-administration by RA patients. We believe this general approach enables the development of optimal biopharmaceuticals.

Elevated sputum interleukin-5 and submucosal eosinophilia in obese individuals with severe asthma

RATIONALE

The relationship between airway inflammation and obesity in severe asthma is poorly understood.

OBJECTIVES

We sought to determine the relationship between sputum mediator profiles and the distribution of eosinophilic inflammation and obesity in people with severe asthma.

METHODS

Clinical parameters and eight mediators in sputum were assessed in 131 subjects with severe asthma from a single center categorized into lean, overweight, and obese groups defined by their body mass index. In an independent group of people with severe asthma (n = 45) and healthy control subjects (n = 19) eosinophilic inflammation was enumerated in bronchial submucosa, blood, and sputum and related to their body mass index.

MEASUREMENTS AND MAIN RESULTS

Sputum IL-5 geometric mean (95% confidence interval) (pg/ml) was elevated in the obese (1.8 [1.2-2.6]) compared with overweight (1.1 [0.8-1.3]; P = 0.025) and lean (0.9 [0.6-1.2]; P = 0.018) subjects with asthma and was correlated with body mass index (r = 0.29; P < 0.001). There was no relationship among body mass index, the sputum cell count, or other sputum mediators. In the bronchoscopy group the submucosal eosinophil number in the subjects with asthma was correlated with body mass index (Spearman rank correlation, rs = 0.38; P = 0.013) and the median (interquartile range) number of submucosal eosinophils was increased in obese (19.4 [11.8-31.2]) (cells per square millimeter) versus lean subjects (8.2 [5.4-14.6]) (P = 0.006). There was no significant association between sputum or peripheral blood eosinophil counts and body mass index.

CONCLUSIONS

Sputum IL-5 and submucosal eosinophils, but not sputum eosinophils, are elevated in obese people with severe asthma. Whether specific antieosinophilic therapy is beneficial, or improved diet and lifestyle in obese asthma has antiinflammatory effects beyond weight reduction, requires further study.

Preclinical development of CAT-354, an IL-13 neutralizing antibody, for the treatment of severe uncontrolled asthma

BACKGROUND AND PURPOSE

IL-13 is a pleiotropic Th2 cytokine considered likely to play a pivotal role in asthma. Here we describe the preclinical in vitro and in vivo characterization of CAT-354, an IL-13-neutralizing IgG4 monoclonal antibody (mAb), currently in clinical development.

EXPERIMENTAL APPROACH

In vitro the potency, specificity and species selectivity of CAT-354 was assayed in TF-1 cells, human umbilical vein endothelial cells and HDLM-2 cells. The ability of CAT-354 to modulate disease-relevant mechanisms was tested in human cells measuring bronchial smooth muscle calcium flux induced by histamine, eotaxin generation by normal lung fibroblasts, CD23 upregulation in peripheral blood mononuclear cells and IgE production by B cells. In vivo CAT-354 was tested on human IL-13-induced air pouch inflammation in mice, ovalbumin-sensitization and challenge in IL-13 humanized mice and antigen challenge in cynomolgus monkeys.

KEY RESULTS

CAT-354 has a 165 pM affinity for human IL-13 and functionally neutralized human, human variant associated with asthma and atopy (R130Q) and cynomolgus monkey, but not mouse, IL-13. CAT-354 did not neutralize human IL-4. In vitro CAT-354 functionally inhibited IL-13-induced eotaxin production, an analogue of smooth muscle airways hyperresponsiveness, CD23 upregulation and IgE production. In vivo in humanized mouse and cynomolgus monkey antigen challenge models CAT-354 inhibited airways hyperresponsiveness and bronchoalveolar lavage eosinophilia.

CONCLUSIONS AND IMPLICATIONS

CAT-354 is a potent and selective IL-13-neutralizing IgG4 mAb. The preclinical data presented here support the trialling of this mAb in patients with moderate to severe uncontrolled asthma.

Expression of the T helper 17-associated cytokines IL-17A and IL-17F in asthma and COPD

Background:

Asthma and COPD are characterized by airway dysfunction and inflammation. Neutrophilic airway inflammation is a common feature of COPD and is recognized in asthma, particularly in severe disease. The T helper (Th) 17 cytokines IL-17A and IL-17F have been implicated in the development of neutrophilic airway inflammation, but their expression in asthma and COPD is uncertain.

Methods:

We assessed IL-17A and IL-17F expression in the bronchial submucosa from 30 subjects with asthma, 10 ex-smokers with mild to moderate COPD, and 27 nonsmoking and 14 smoking control subjects. Sputum IL-17 concentration was measured in 165 subjects with asthma and 27 with COPD.

Results:

The median (interquartile range) IL-17A cells/mm² submucosa was increased in mild to moderate asthma (2.1 [2.4]) compared with healthy control subjects (0.4 [2.8]) but not in severe asthma (P = .04). In COPD, IL-17A⁺ cells/mm² submucosa were increased (0.5 [3.7]) compared with nonsmoking control subjects (0 [0]) but not compared with smoking control subjects (P = .046). IL-17F⁺ cells/mm² submucosa were increased in severe asthma (2.7 [3.6]) and mild to moderate asthma (1.6 [1.0]) compared with healthy controls subjects (0.7 [1.4]) (P = .001) but was not increased in subjects with COPD. IL-17A and IL-17F were not associated with increased neutrophilic inflammation, but IL-17F was correlated with the submucosal eosinophil count (rs = 0.5, P = .005). The sputum IL-17 concentration in COPD was increased compared with asthma (2 [0-7] pg/mL vs 0 [0-2] pg/mL, P < .0001) and was correlated with post-bronchodilator FEV₁% predicted (r = −0.5, P = .008) and FEV₁/FVC (r = −0.4, P = .04).

Conclusions:

Our findings support a potential role for the Th17 cytokines IL-17A and IL-17F in asthma and COPD, but do not demonstrate a relationship with neutrophilic inflammation.

Short-term exposure to transforming growth factor β induces long-term fibrotic responses

Transforming growth factor beta (TGFbeta), a potent inducer of cell transdifferentiation, is heavily implicated in fibrotic disorders. Following cataract surgery, aberrant cell growth across the collagenous matrix of the lens capsule leads to fibrosis, and in turn secondary visual loss, known as posterior capsule opacification (PCO). These modifications are associated with transdifferentiated cells. Following surgery, protein levels in the eye transiently increase, lasting a matter of days whereas PCO takes much longer to reach clinical significance. In the present study, a human lens culture model was employed to show that a relatively brief 2-day exposure to TGFbeta gives rise to persistent, long-term signalling events resulting 28 days later in matrix contraction and transdifferentiation. These events can be suppressed by application of the human monoclonal anti-TGFbeta2 antibody CAT-152 either simultaneously or after TGFbeta2 exposure. Radiolabel binding studies revealed the lens capsule serves as a store for TGFbeta2. Importantly, similar binding studies showed that the capsule could also serve as a reservoir for CAT-152. The data reveal the longevity of TGFbeta2 action through matrix association, but also demonstrate how early application of a TGFbeta2 antibody can overcome the detrimental TGFbeta actions leading to potential inhibition of PCO development and other fibrotic disorders.

Measurement of eotaxin (CCL11) in induced sputum supernatants: validation and detection in asthma

BACKGROUND

Induced sputum is widely used in asthma research; however, for many mediators, the detection methods have not been validated.

OBJECTIVE

We sought to optimize the method of detection of eotaxin, an important chemokine acting through the CCR3 receptor on eosinophils, basophils, and T(H)2 cells.

METHODS

Induced sputum from normal and asthmatic subjects was processed with dithioerythritol (DTE) or PBS; recovery of eotaxin was assessed by means of ELISA before and after spiking with recombinant eotaxin. Furthermore, the effects of removing DTE by means of ultrafiltration or the addition of protease inhibitors and high-speed centrifugation on endogenous levels and spiking recovery of eotaxin were assessed.

RESULTS

Endogenous eotaxin was undetectable in DTE-processed samples, with a mean of only 30% (SD, 13%) spike recovery. DTE had no effect on the immunoassay capture antibody but dramatically reduced the detection of recombinant eotaxin. Removal of DTE from sputum before immunoassay did not improve detection, although it restored the recovery of a subsequent eotaxin spike. In contrast, PBS-processed sputum resulted in an eotaxin spike recovery of 101% (SD, 20%). Addition of protease inhibitors or high-speed centrifugation had no effect on eotaxin detection. By using this optimized protocol, eotaxin levels in PBS-processed sputum samples were found to be significantly increased in asthmatic sputum (P<.05).

CONCLUSION

Measurement of eotaxin by means of immunoassay is adversely affected by DTE, possibly through irreversible denaturation of epitopes, which makes eotaxin undetectable by using the immunoassay antibody. Sputum samples should be processed into PBS for assessment of eotaxin, which is present at increased levels in asthmatic sputum.

Contribution of eotaxin-1 to eosinophil chemotactic activity of moderate and severe asthmatic sputum

The CC chemokine eotaxin-1 (CCL11) is chemotactic for eosinophils, basophils, and type 2 helper T cells and may play a role in allergic inflammation. We investigated its contribution as an eosinophil chemoattractant in asthmatic airway secretions (sampled as induced sputum), which possess chemotactic activity for eosinophils and T cells. Sputum samples collected from healthy subjects and subjects with mild, stable-moderate, unstable-moderate, and severe asthma were processed with phosphate-buffered saline and assayed for eotaxin by ELISA and for eosinophil chemotactic activity by fluorescence-based chemotaxis assay. The contribution of eotaxin to chemotactic activity was studied by using a high-affinity neutralizing human anti-eotaxin antibody, CAT-213. Sputum eotaxin concentration was significantly raised in moderate and severe asthma (p < 0.05 versus healthy control subjects) but not in mild asthma. Chemotactic activity was significantly increased in all asthmatic groups relative to healthy subjects (p < 0.05) and was significantly inhibited by CAT-213 (100 nM) in subjects with moderate and severe asthma, with median inhibition of 52% (p < 0.05), 78% (p < 0.0001), and 86% (p < 0.0001), respectively, in samples representing stable-moderate, unstable-moderate, and severe asthma. Eotaxin contributed to the eosinophil chemotactic activity of sputum from subjects with more severe forms of asthma but not mild asthma, suggesting that its contribution is more important in more severe disease. This activity is inhibited significantly by CAT-213.

Evaluation of anti-TGF-beta2 antibody as a new postoperative anti-scarring agent in glaucoma surgery

PURPOSE

Postoperative subconjunctival wound healing remains the commonest cause of late bleb failure after glaucoma filtration surgery. This study was undertaken to investigate whether the human monoclonal antibody that neutralizes transforming growth factor-beta2 (CAT-152; lerdelimumab) could be used as a postoperative agent to prevent scarring after glaucoma surgery and compared it with 5-fluorouracil (5-FU), to benchmark its potential clinical benefit.

METHODS

In a randomized, controlled, masked-observer study, after modified glaucoma surgery, 48 rabbits were randomly allocated to receive a postoperative course of seven subconjunctival injections of CAT-152 (1 mg/mL), 5-FU (50 mg/mL), or no treatment. Bleb characteristics, the presence of subconjunctival drainage, and local reaction to treatment were assessed. Animals were killed on days 10, 21, and 30. Immunohistochemistry, histologic staining and electron microscopy were performed to demonstrate the mechanism of CAT-152-mediated effects on the extracellular matrix.

RESULTS

CAT-152 significantly improved surgical outcome (log rank test, P < 0.001) and reduced subconjunctival collagen deposition (P < 0.01) compared with 5-FU and control. Median bleb survival was increased in the CAT-152 group (23.5 days) compared with the 5-FU (20 days) and control (16 days) treatment groups. CAT-152 treatment improved bleb morphology (P < 0.05) and was well tolerated. 5-FU prolonged the duration of corneal epitheliopathy (P < 0.01).

CONCLUSIONS

Postoperative administration of CAT-152 significantly improved surgical outcome, reduced subconjunctival scarring, and minimized the risk of corneal side effects compared with the anti-scarring agent 5-FU. These findings suggest that CAT-152 may offer therapeutic benefit as a postoperative agent to prevent subconjunctival scarring after glaucoma filtration surgery.

Oxidative neuropathology and putative chemical entities for Alzheimer's disease: neuroprotective effects of salen-manganese catalytic anti-oxidants

Considerable evidence exists that the brains of individuals with Alzheimer's disease are subject to elevated levels of oxidative stress, particularly in regions exhibiting pathological damage. A major contributor to this oxidative stress appears to be the inflammatory process. Activation of rodent microglial cells by LPS or beta-amyloid peptide results in a marked up-regulation of inducible nitric oxide synthase (iNOS) and corresponding nitric oxide (NO) production. Elevated levels of iNOS are also observed in the brains of Alzheimer patients. The reaction of NO with superoxide leads to the generation of the highly reactive and damaging peroxynitrite free radical species. Peroxynitrite appears to play a key role in the generation of an oxidative stress in the Alzheimer brain as evidenced by widespread nitrotyrosine immunoreactivity. We have employed SIN-1 as a peroxynitrite generating system in cell cultures in order to characterize the effects of this free radical on neurons. SIN-1 treatment of primary rat hippocampal neurons in culture results in neurotoxicity by a necrosis mechanism according to electron microscopic criteria. One approach to limiting peroxynitrite mediated damage is to limit superoxide production. An approach we have evaluated is treatment with salen manganese compounds, a class of catalytic antioxidant compounds which behave as superoxide dismutase (SOD)/catalase mimetics to detoxify superoxide. A number of such salen manganese compounds, including EUK-8 and EUK-134, can markedly protect primary rat cortical neurons from hydrogen peroxide mediated oxidative stress. Such salen manganese compounds can similarly afford marked neuroprotection to an oxidative stress imposed by SIN-1, potentially attributable at least in part to their inherent SOD activity. The salen manganese SOD/catalase mimetics represent a promising class of catalytic antioxidant for attenuating oxidative stress.

The antihypertensive profile of the angiotensin AT1 receptor antagonist, GR138950, and the influence of potential homeostatic compensatory mechanisms in renal hypertensive rats

The cardiovascular profile of the angiotensin AT1 receptor antagonist, GR138950, and the influence of potential compensatory homeostatic mechanisms on this profile, were investigated in renal artery ligated hypertensive (RALH) rats. GR138950 caused a marked reduction in blood pressure associated with immediate tachycardia in conscious RALH rats. The antihypertensive action of GR138950 appeared biphasic; an immediate fall in blood pressure, which plateaued within 1 h, and which was followed by a further slow decline that reached maximum between 5-7 h after administration. The tachycardia caused by GR138950 was attenuated by atenolol and was abolished by combined pretreatment with atenolol and atropine methyl nitrate. However, the antihypertensive profile of GR138950 was unchanged by these pretreatments. The resting blood pressure and the antihypertensive effect of GR138950, in RALH rats, were unaffected by the vasopressin V1 receptor antagonist, [beta-mercapto-beta,beta-cyclopentamethylene propionyl(1)-O-Me-Tyr2,Arg8]-vasopressin. Thus, vasopressinergic mechanisms are not involved in either maintaining blood pressure in RALH rats, or in compensating for the fall in blood pressure caused by GR138950. In anaesthetized RALH rats, GR138950 caused a marked fall in blood pressure that was accompanied by an increase in heart rate along with sustained increases in renal and splanchnic sympathetic nerve activity. In summary, the biphasic fall in blood pressure evoked by GR138950 in RALH rats can not be explained on the basis of changes in autonomic control of the heart, alteration of vasopressin-mediated vasoconstrictor mechanisms or overall suppression of central sympathetic outflow. Rather, increased vasoconstrictor tone might serve to oppose the initial fall in blood pressure.

Investigation of the inhibitory effect of N(G)-nitro-L-arginine methyl ester on the antihypertensive effect of the angiotensin AT1 receptor antagonist, GR138950

1. The effect of systemic administration of the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) on the antihypertensive effects of the angiotensin AT1 receptor antagonist, GR138950, the angiotensin-converting enzyme (ACE) inhibitor, enalapril, or hydralazine has been evaluated in unrestrained, conscious renal artery ligated hypertensive (RALH) rats. The effect of the phosphodiesterase type V inhibitor, zaprinast on the antihypertensive effect of GR138950 in RALH rats was also examined. The effect of GR138950 on blood pressure, and plasma and urine cyclic GMP levels was compared to that of zaprinast in conscious RALH rats. 2. GR138950, enalapril or hydralazine caused marked reductions in blood pressure associated with immediate tachycardia in conscious RALH rats. L-NAME pretreatment attenuated the antihypertensive effects of GR138950 or enalapril but not that of hydralazine in conscious RALH rats. The initial tachycardia caused by GR138950 or enalapril but not hydralazine was attenuated by L-NAME pretreatment. L-NAME alone caused a transient (20 min) pressor response and a prolonged (6 h) bradycardia in conscious RALH rats. 3. Pretreatment with indomethacin did not affect the cardiovascular effect of GR138950 in conscious RALH rats. Indomethacin alone did not significantly change basal blood pressure or heart rate in RALH rats. 4. Zaprinast pretreatment did not affect the antihypertensive effect of GR138950 in conscious RALH rats but potentiated the depressor response to sodium nitroprusside. Zaprinast alone caused a small reduction in basal blood pressure but did not change basal heart rate in RALH rats. 5. The antihypertensive effect of GR138950 was not associated with an increase in plasma or urine cyclic GMP levels in conscious RALH rats, whereas zaprinast caused a small fall in blood pressure associated with increases in plasma and urine cyclic GMP. 6. The ability of L-NAME to inhibit the antihypertensive action of GR138950 or enalapril suggests that these agents release nitric oxide (NO) and/or enhance the cardiovascular effects of NO as part of their mechanism of action. However, the inability of zaprinast to potentiate the antihypertensive effects of GR138950 and the finding that GR138950 did not increase urine and plasma cyclic GMP levels are not consistent with this view. Attenuation of the response to GR138950 or enalapril, but not hydralazine, suggests a selective interaction between L-NAME and inhibitors of the renin-angiotensin system, although the nature of this interaction is unknown.

Cardiovascular effects of serotonin and DP-5-CT in conscious Long-Evans and Brattleboro rats

The regional hemodynamic changes caused by intracerebroventricular 5-hydroxytryptamine (5-HT) were investigated in conscious Long-Evans and Brattleboro rats with chronically implanted Doppler flow probes. In both strains, a low dose of 5-HT (4 nmol/kg) caused a pressor response associated with tachycardia, mesenteric vasoconstriction, and a transient hindquarters vasodilatation. In Long-Evans rats, higher doses of 5-HT (40 and 120 nmol/kg) caused a pressor response, a bradycardia, mesenteric vasoconstriction, and maintained hindquarters dilatation. The bradycardia and mesenteric vasoconstriction caused by 40 nmol/kg of 5-HT in Long-Evans rats were attenuated by d(CH2)5Tyr(Me)arginine vasopressin, a V1-receptor antagonist. In Brattleboro rats the high doses of 5-HT failed to cause a pressor response but caused a delayed depressor response, a transient tachycardia, less mesenteric vasoconstriction, and a larger initial hindquarters dilatation compared with Long-Evans rats. The initial part of the hindquarters vasodilator response caused by 120 nmol/kg of 5-HT in Brattleboro rats was attenuated by the beta 2-adrenoceptor antagonist ICI-118551. In Long-Evans rats, N,N-di-n-propyl-5-carboxamidotryptamine maleate (DP-5-CT; 3, 30, and 100 nmol/kg icv), a 5-HT1A receptor agonist, caused a tachycardia associated with a marked hindquarters vasodilatation. These changes were accompanied by a weak mesenteric vasoconstriction and, for the highest dose of DP-5-CT, a pressor response. These data overall are consistent with the hemodynamic effects of intracerebroventricular 5-HT contingent on vasopressin release and, along with DP-5-CT, sympathoadrenal excitation; however, additional mechanisms are indicated.

Evidence that activation of 5-HT2 receptors in the forebrain of anaesthetized cats causes sympathoexcitation

1. The aim of the present experiments was to determine whether the effects of lateral ventricular application of 5-HT on cardiovascular and respiratory variables in anaesthetized cats are mediated by forebrain 5-HT2 receptors. This was carried out by determining whether the effects of 5-HT are blocked by the 5-HT2 antagonist, cinanserin and if they are mimicked by the selective 5-HT2 agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). 2. Cats were anaesthetized with a mixture of alpha-chloralose and pentobarbitone sodium, neuromuscularly blocked and artifically ventilated. The following cardiovascular and respiratory variables were recorded: renal, splanchnic and cardiac sympathetic nerve activities, phrenic nerve activity, heart rate, arterial blood pressure, femoral arterial conductance and tracheal pressure. All drugs were administered via the lateral ventricle and the action of these agonists was restricted to forebrain sites by a cannula placed in the Aqueduct of Sylvius. 3. Cumulative doses of 5-HT (10-160 nmol kg-1) and DOI (80-320 nmol kg-1) injected into the lateral ventricle caused significant increases in blood pressure, heart rate, cardiac and splanchnic sympathetic nerve activity and a decrease in femoral arterial conductance. DOI and 5-HT caused a greater increase in cardiac compared with splanchnic nerve activity and failed to change renal nerve activity. 5-HT but not DOI significantly increased the magnitude and the number of phrenic bursts as well as significantly increasing tracheal pressure. The effects of 5-HT also differed from DOI in that 5-HT evoked maximal pressor and near maximal sympathoexcitatory effects after the first dose, whereas the pressor and sympathoexcitatory effects of DOI were graded over the complete dose-range.4 The 5-HT2 antagonist, cinanserin (265 nmol kg-1, i.c.v.) caused significant falls in blood pressure,heart rate and cardiac nerve activity and an increase in femoral arterial conductance. Splanchnic andrenal sympathetic nerve activity, phrenic nerve activity and tracheal pressure were unaffected by cinanserin. After pretreatment with cinanserin all cardiovascular and respiratory effects of 5-HT were significantly attenuated.5 It is concluded that in the cat, as DOI and 5-HT have similar effects on the cardiovascular variables recorded and as the effects of 5-HT are blocked by cinanserin, 5-HT can act on 5-HT2 receptors located in the forebrain to cause differential sympathoexcitation and a rise in arterial blood pressure. Further,the sympathoexcitatory effects mediated by 5-HT2 receptors located in the forebrain differ from those located in the hindbrain in that they mediate increases in cardiac nerve activity and heart rate and also have no effect on renal nerve activity.

Central administration of 5-HT activates 5-HT1A receptors to cause sympathoexcitation and 5-HT2/5-HT1C receptors to release vasopressin in anaesthetized rats

1. The effects of intracerebroventricular injections to the right lateral ventricle (i.c.v.) of 5-hydroxytryptamine (5-HT, 40 and 120 nmol kg-1), N,N-di-n-propyl-5-carboxamidotryptamine (DP-5-CT; 3 nmol kg-1), 5-carboxamidotryptamine (5-CT; 3 nmol kg-1), 8-hydroxy-2-(di-N-propylamino) tetralin (8-OH-DPAT; 3, 40 and 120 nmol kg-1) and 1-(2,5-di-methoxy-4-iodophenyl)-2-aminopropane (DOI; 40 and 120 nmol kg-1) on renal sympathetic nerve activity, blood pressure, heart rate and phrenic nerve activity were investigated in normotensive rats anaesthetized with alpha-chloralose. 2. 5-HT caused a long lasting pressor response which was associated with an initial bradycardia and renal sympathoinhibition followed by a tachycardia and renal sympathoexcitation. Pretreatment with the 5-HT2/5-HT1C receptor antagonists, cinanserin (300 nmol kg-1, i.c.v.) or LY 53857 (300 nmol kg-1, i.c.v.) reversed the initial bradycardia and sympathoinhibition to tachycardia and sympathoexcitation. Combined pretreatment with LY 53857 (300 nmol kg-1, i.c.v.) and the 5-HT1A antagonist, spiroxatrine (300 nmol kg-1, i.c.v.), blocked the effects of 5-HT on all the above variables. 3. Pretreatment with the vasopressin V1-receptor antagonist, beta-mercapto-beta,beta-cyclopentamethylene-propionyl1, O-Me-Tyr2, Arg8-vasopressin [(d(CH2)5Tyr(Me)AVP, 10 micrograms kg-1, i.v.] did not affect the magnitude but reduced the duration of the pressor response produced by i.c.v. 5-HT and reversed the initial bradycardia and renal sympathoinhibition to tachycardia and sympathoexcitation. 4. 1-(2,5-Di-methoxy-4-iodophenyl)-2-aminopropane (DOI) caused a pressor effect which was associated with a bradycardia and sympathoinhibition. These effects were blocked by pretreatment with BWSOlC67 (0.1 mg kg-', i.v.), a peripherally acting 5-HT2/5-HTc receptor antagonist. However,BWSOlC67 (0.1 mg kg-', i.v.) failed to block the effects of i.c.v. 5-HT.5. DP-5-CT, 5-CT and 8-OH-DPAT (3 nmol kg-', i.c.v.) caused sympathoexcitation, tachycardia and a rise in blood pressure. Pretreatment with methiothepin (1 mg kg-', i.v.) or spiroxatrine (300 nmol kg-',i.c.v.) attenuated the response to i.c.v. DP-5-CT.6. It is concluded that i.c.v. administration of 5-HT activates 5-HTlA receptors to cause sympathoexcitation and 5-HT2 or 5-HT1c receptors to cause the release of vasopressin.

Physical characteristics and ventilatory function of 404 commercial divers working in the North Sea

The physical characteristics and simple lung ventilatory indices (FVC, FEV 1, FEV 1/FVC) of 404 commercial divers employed by companies operating in the North Sea were analysed. These findings were correlated with the diving experience and maximum operating depth of each diver. All the divers were men of average height 176-9 cm, and weight 77-1 kg which is greater than average for active Western males, but only 6% were more than 120% of their predicted weight. The average duration of commercial diving was 7-1 years, 11% of divers having less than one year's experience. Sixty-seven per cent had worked at a maximum depth of 200 ft (61 m) and only 6% had worked deeper than 500 ft (153 m). The mean forced vital capacity (FVC) was 120-4% of the predicted value which indicated that they could voluntarily move large amounts of gas in and out of their lungs. This was greatest in the divers who when deepest. The mean forced expired volume in one second (FEV 1) was 117% of the predicted value showing that expiratory airflow capacity was also increased, but to a lesser extent than the FVC. Thper and activated by zinc. Plasma protein protected the enzyme from both inhibition and activation. ALAD activity was found to be an indicator of the total metal ion concentration in the blood and was therfore considered to be of doubtful value in screening large population for increased lead absorption.