Adhesion to fibronectin prolongs eosinophil survival

We have investigated the effect of adhesion to fibronectin (Fn) on the survival of eosinophils in culture. Peripheral blood eosinophils from normal human donors were separated by immunomagnetic selection and cultured in RPMI on Fn- (100 micrograms/ml) coated microtiter plates for up to 96 h. Survival was measured by trypan blue exclusion. There was a significant enhancement of eosinophil survival with Fn as compared with both bovine serum albumin-coated and uncoated wells (p < 0.05-0.01). Fn-induced eosinophil survival was comparable to that obtained with exogenous interleukin 3 (IL-3) or granulocyte/macrophage colony-stimulating factor (GM-CSF) and was inhibitable by antibodies against Fn, very late antigen 4 (VLA-4), IL-3, and GM-CSF. Supernatants from Fn-, but not BSA-coated wells contained picogram amounts of IL-3 and GM-CSF, and eosinophils cultured on Fn for 24 h expressed mRNA for GM-CSF as determined by in situ hybridization. Therefore, Fn prolongs eosinophil survival in culture by triggering autocrine generation of cytokines by eosinophils. Since neutrophils lack VLA-4, this could provide a partial explanation for the preferential accumulation of eosinophils at sites of allergic inflammation, as well as the predominant tissue localization of eosinophils in healthy individuals.

Human eosinophil, but not neutrophil, adherence to IL-1-stimulated human umbilical vascular endothelial cells is alpha 4 beta 1 (very late antigen-4) dependent

Eosinophils, through their ability to generate an array of potent mediators, are thought to be the major effector cells in a number of conditions, including parasitic infection, asthma, and other allergic diseases. The mechanism(s) by which eosinophils, as opposed to neutrophils, accumulate at inflammatory sites is unknown. One possible mechanism would be an eosinophil-specific pathway of adhesion to vascular endothelium. In this study we have demonstrated that human eosinophils, but not neutrophils, constitutively express alpha 4 beta 1 (CD49d/CD29). Expression was not increased on low density eosinophils or normal density cells stimulated with platelet-activating factor. Eosinophils, but not neutrophils, specifically adhered to COS cells transfected with vascular adhesion molecule-1 in a alpha 4 beta 1-dependent manner. Eosinophil, but not neutrophil, adhesion to IL-1 stimulated human umbilical vascular endothelial cells was significantly inhibited by alpha 4 beta 1 mAb at both 5 h (p less than 0.05) and 20 h (p less than 0.001). Inhibition of both resting and platelet-activating factor-(10(-7) M) stimulated eosinophil adhesion was observed. We conclude that the alpha 4 beta 1/vascular adhesion molecule-1 adhesion pathway may be involved in specific eosinophil, as opposed to neutrophil, migration into sites of eosinophilic inflammation.

Human eosinophil, but not neutrophil, adherence to IL-1-stimulated human umbilical vascular endothelial cells is alpha 4 beta 1 (very late antigen-4) dependent

Eosinophils, through their ability to generate an array of potent mediators, are thought to be the major effector cells in a number of conditions, including parasitic infection, asthma, and other allergic diseases. The mechanism(s) by which eosinophils, as opposed to neutrophils, accumulate at inflammatory sites is unknown. One possible mechanism would be an eosinophil-specific pathway of adhesion to vascular endothelium. In this study we have demonstrated that human eosinophils, but not neutrophils, constitutively express alpha 4 beta 1 (CD49d/CD29). Expression was not increased on low density eosinophils or normal density cells stimulated with platelet-activating factor. Eosinophils, but not neutrophils, specifically adhered to COS cells transfected with vascular adhesion molecule-1 in a alpha 4 beta 1-dependent manner. Eosinophil, but not neutrophil, adhesion to IL-1 stimulated human umbilical vascular endothelial cells was significantly inhibited by alpha 4 beta 1 mAb at both 5 h (p less than 0.05) and 20 h (p less than 0.001). Inhibition of both resting and platelet-activating factor-(10(-7) M) stimulated eosinophil adhesion was observed. We conclude that the alpha 4 beta 1/vascular adhesion molecule-1 adhesion pathway may be involved in specific eosinophil, as opposed to neutrophil, migration into sites of eosinophilic inflammation.

Effects of cetirizine on human eosinophil and neutrophil activation in vitro

The ability of cetirizine, a novel antihistamine agent, to inhibit the in vivo activation of human eosinophils, neutrophils and monocytes has been investigated using C3b- and IgG-dependent rosette formation, cytotoxicity against opsonised parasitic larvae and adherence to plasma-coated glass (PCG). The drug inhibited platelet-activating factor (PAF)-induced enhancement of eosinophil and neutrophil IgG (Fc) and complement (C3b) rosettes with an IC50 of 2 x 10(-5) M. There was also comparable inhibition of PAF-dependent enhancement of eosinophil cytotoxicity (for complement-coated schistosomula of Schistosoma mansoni). Cetirizine inhibited PAF-induced eosinophil, but not neutrophil, hyperadherence to PCG. These data support the view that cetirizine may exert some of its anti-allergic effects by inhibiting the activation of human granulocytes and that it may also selectively inhibit PAF-induced eosinophil hyperadherence.

Interleukin-5 enhances the in vitro adhesion of human eosinophils, but not neutrophils, in a leucocyte integrin (CD11/18)-dependent manner

Interleukin (IL-5) was found to enhance the adhesion of eosinophils, but not neutrophils, to both microvascular and large vein endothelial cells in a dose-dependent manner. Granulocyte/macrophage-colony-stimulating factor (GM-CSF) and platelet-activating factor (PAF) enhanced both eosinophil and neutrophil adhesion. Significant increases in eosinophil CR3 expression, but not LFA-1, were observed following pre-incubation with PAF, IL-3, IL-5 or GM-CSF. Neutrophil CR3 expression was increased significantly by pre-incubation with PAF or GM-CSF, but not IL-3 or IL-5. Enhanced adhesion to human microvascular endothelial cells (HMVEC) or human umbilical vein endothelial cells (HUVEC) was inhibited by (ranked in order of potency) anti-CR3 alpha = common beta-chain greater than LFA-1 alpha. Anti-p150,95 alpha had no measurable effect. Basal expression of eosinophil CR3 with monoclonal antibody inhibited IL-5-induced eosinophil hyperadherence to HUVEC in a manner almost identical to inhibition in the presence of excess anti-CR3. Thus, a conformational or affinity change in adhesion receptors following activation seems more important than a simple increase in numbers. No inhibition of unstimulated eosinophil adhesion to HMVEC or HUVEC by CD11/18 monoclonal antibody was observed. These findings demonstrate that IL-5 enhances eosinophil, but not neutrophil, adherence reactions, by a mechanism dependent, at least in part, on the CD11/18 family of adhesion glycoproteins.

IL-5 enhances the in vitro adhesion of human eosinophils, but not neutrophils, in a leucocyte integrin (CD11/18)-dependent manner

In an attempt to explain the preferential accumulation of eosinophils at sites of allergic tissue reactions, we have studied the effects of interleukin-5 (IL-5) on the adherence of human eosinophils and neutrophils to plasma-coated glass (PCG) or human microvascular endothelial cells (HMVEC). IL-5 was compared with IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF) and platelet-activating factor (PAF), since all these agents have biological properties associated with eosinophil activation and/or survival in vitro. IL-5, IL-3 and GM-CSF induced a time-dependent increase in adherence of normal density eosinophils to PCG optimal at 60 min, whereas the effect of PAF was greater at 15 min. Similar results were obtained with neutrophils, with the exception that IL-5 had minimal and non-significant effects on this cell type. Unstimulated eosinophils and neutrophils also adhered to PCG or HMVEC, but in low numbers. Preincubation of eosinophils with IL-5, GM-CSF or PAF resulted in dose-dependent increases in the numbers of adherent cells to PCG. IL-3 had a smaller but significant effect on enhanced eosinophil adhesion to PCG, while IL-2 and lyso-PAF were ineffective. Neutrophils gave similar levels of baseline and stimulated adhesion to PCG as eosinophils, IL-5 again had no significant stimulatory effect. IL-5 also increased eosinophil, but not neutrophil, adherence to HMVEC in a concentration-dependent manner. Preincubation with the protein synthesis inhibitor cycloheximide had no effect on IL-5-, GM-CSF- or PAF-stimulated eosinophil adhesion. The contribution of the CD11/18 leucocyte integrins to IL-5- and PAF-induced eosinophil hyperadherence was investigated by inhibition experiments utilizing monoclonal antibodies (mAb). Enhanced adhesion to PCG (by PAF) or HMVEC (by IL-5) was inhibited by (ranked in order of potency) anti-CR3 alpha = common beta-chain greater than LFA-1 alpha. Anti-p150,95 alpha had no measurable effect. Baseline adhesion by unstimulated eosinophils was not significantly influenced by prior incubation with these mAb. Using flow cytometry, IL-5 and IL-3 were found to up-regulate cosinophil but not neutrophil CR3 expression. These findings demonstrate that IL-5 enhances cosinophil, but not neutrophil, adherence reactions, by a mechanism dependent, at least in part, on the CD11/18 family of adhesion glycoproteins.

Receptor expression and functional status of cultured human eosinophils derived from umbilical cord blood mononuclear cells

Selective use of recombinant human cytokines has enabled the culture of large numbers of eosinophils from human cord blood mononuclear cells, raising the possibility of their use as a model of eosinophil function. Cultured eosinophils (CE) were compared with normal-density peripheral blood eosinophils (PBE) in terms of their membrane receptor expression and function. Fc gamma R and CR1 expression of CE and PBE was similar. In contrast, the specific mean fluorescence for LFA-1 alpha, p150,95 alpha, ICAM-1, and HLA-DR was significantly elevated for CE compared with PBE. CE responded in PAF-induced chemotaxis in a similar fashion to PBE. CE gave higher numbers of both resting and platelet activating factor (PAF)-stimulated immunoglobulin G (IgG)- and C3b-dependent rosettes than PBE. CE and PBE had comparable capacity to kill IgG- and C-opsonized schistosomula in terms of both baseline values and PAF-induced enhancement of cytotoxicity. Baseline adherence by CE and PBE to plasma-coated glass was essentially the same, but stimulated adhesion (PAF) of CE was lower. Compared with PBE, CE generated less than half the amounts of extracellular and cell-associated PAF induced by calcium ionophore A23187 stimulation. Unlike PBE, CE did not generate PAF after exposure to IgG-coated Sepharose particles. CE stimulated with IgG-coated beads generated small quantities of LTC4, while A23187 stimulation resulted in approximately half the LTC4 levels observed with PBE. The total cell content of eosinophil peroxidase (EPO) was similar for CE and PBE. These data suggest that although CE and PBE have many phenotypic and functional properties in common there are quantitative differences that may be a consequence of their immaturity and/or the influence of the cytokines used in their culture.

The effect of platelet-activating factor on IgE binding to, and IgE-dependent biological properties of, human eosinophils

This study investigated the effect of platelet-activating factor (PAF), leukotriene B4 (LTB4) histamine and formyl-methionyl-leucyl-phenylalanine (FMLP) on immunoglobulin E (IgE) binding and IgE-dependent cytotoxicity of human normal density eosinophils. The binding of a native myeloma IgE to normal human eosinophils was measured by flow cytometry using a fluorescein-conjugated polyclonal anti-IgE antibody. Preincubation with PAF (optimal at 10(-7)M), but not lyso-PAF or FMLP, gave dose-dependent increases in IgE binding. PAF and LTB4 gave significant increases in IgE binding after 5 min preincubation (P less than 0.05); the effect was further enhanced at 30 min (P less than 0.01). This was further confirmed using the rosette assay where PAF and LTB4, but not lyso-PAF or FMLP, gave dose- and time-dependent increases in IgE eosinophil rosettes. Eosinophil cytotoxicity for schistosomula of Schistosoma mansoni, incubated with immune serum, was also significantly enhanced (P less than 0.01) by PAF in a dose-dependent fashion (optimal at 10(-8) M). Schistosomula coated with FPLC-purified IgE fractions were susceptible to killing by normal density eosinophils, and this was enhanced with PAF (10(-8)M), LTB4 (10(-7)M) and histamine (10(-5)M) but not with FMLP (10(-7)M) or lyso-PAF. IgE-dependent cytotoxicity was confirmed by the removal of contaminating IgG from IgE-rich fractions, and by the abolishment of IgE-dependent cytotoxicity after IgE adsorption. These results suggest that PAF (and to a lesser extent LTB4 and histamine) increase IgE binding, IgE-dependent adherence and cytotoxicity of normal human eosinophils. Although IgE receptors have not been identified, the data support current concepts that certain biological properties of eosinophils may be IgE associated.

Fc gamma and CD11/CD18 receptor expression on normal density and low density human eosinophils

We have studied the expression of Fc gamma receptors and leucocyte integrins (CD11/CD18 family) on human eosinophils using specific monoclonal antibodies (mAb) and flow cytometric analysis. Peripheral blood eosinophils of normal density and low density were compared with neutrophils and monocytes. Several properties of the human eosinophil were established. These were (i) that the eosinophil expressed Fc gamma RII (CDw32) only (unlike monocytes which bear Fc gamma RI and Fc gamma RII and neutrophils which bear Fc gamma RII and Fc gamma RIII); (ii) that the absence of Fc gamma RIII (CD16) on eosinophils served as a basis for distinguishing eosinophil and neutrophil populations by immunofluorescence; (iii) that the leucocyte adhesion glycoproteins, LFA-1 alpha (CD11a), CR3-alpha (CD11b), p150, 95-alpha (CD11c) and the common beta-chain (CD18), were expressed on the eosinophil as well as the neutrophil; (iv) that CD18 expression was significantly reduced on low-density eosinophils from the hypereosinophilic syndrome. Thus, our findings emphasize the unique phenotype of the human eosinophil in terms of Fc gamma receptor expression, the similarity of the eosinophil and neutrophil with regard to the leucocyte integrins and that eosinophils of low density do not differ greatly from those of normal density in terms of receptor expression.

A case of exercise-induced anaphylaxis: evidence of an association with the complement system

We studied a 17-year-old girl with exercise-induced anaphylaxis (EIA). She experienced 10 episodes of EIA which demonstrated cutaneous, digestive and cardiorespiratory symptoms. This subject exhibited elevation in plasma histamine (13.3 ng/ml) and decrease in CH50 (17 U/ml) and C3 (70 mg/dl) after naturally induced EIA. On remission day CH50 (26 U/ml), C3 (83 mg/dl) and C4 (15 mg/dl) were of relatively low values. Her mother demonstrated the same tendency with a low level of C4 (14 mg/dl), and this suggested an underlying genetic disorder in the complement system. Exercise challenge could not elicit EIA symptomatically but showed fluctuation of CH50. The triggering mechanism of EIA was unclear; however there is a possibility that complement plays an important role in EIA.

Flow-cytometric analysis of increased IgE uptake by normal eosinophils following activation with PAF-acether and other inflammatory mediators

Using flow-cytometric analysis and a fluorescein-conjugated anti-IgE antibody, we have investigated whether normal-density human eosinophils will bind greater amounts of native IgE following activation with platelet-activating factor (PAF), leukotriene B4 (LTB4) and histamine. Incubation with PAF resulted in a large dose- and time-dependent increase in IgE binding, optimal at 10(-7) M and 30 min, respectively. LTB4 and histamine gave lower but significant increases in IgE binding. Enhanced binding of IgE by activated normal-density eosinophils is probably a consequence of enhanced Fc epsilon RII receptor expression, suggesting a functional role for this receptor in allergic inflammation.

Effects of verapamil and nifedipine on systemic hemodynamics in spontaneously hypertensive rats

Verapamil (1 mg/kg, i.v.) and nifedipine (0.3 mg/kg, i.v.) were tested at equi-antihypertensive doses for systemic hemodynamic responses in conscious spontaneously hypertensive rats (SHR) using the Fick method. Systemic hemodynamic effects of these agents were also evaluated in areflexic, spinal cord-transected and vagotomized SHR using the electromagnetic flowmetry technique. Both verapamil and nifedipine lowered mean arterial pressure (MAP:verapamil = -24%; nifedipine = -28%) in conscious SHR by decreasing total peripheral resistance (TPR:verapamil = -48%; nifedipine = -59%) with a concomitant rise in cardiac output (CO: verapamil = 48%; nifedipine = 86%) and stroke volume (SV:verapamil = 54%; nifedipine = 65%), but verapamil prevented tachycardia, whereas nifedipine increased heart rate (HR:13%). Verapamil and nifedipine also altered systemic hemodynamics in the areflexic SHR; verapamil reduced MAP (-31%) by reducing CO (-18%) with associated bradycardia (-25% HR), whereas nifedipine also lowered MAP (-21%) by decreasing TPR (-18%) without changes in CO and HR. It is concluded that, firstly, the antihypertensive action of verapamil and nifedipine in conscious SHR is due to systemic vasodilation that is associated with reflexly increased CO; secondly, that verapamil has a direct negative chronotropic effect, but nifedipine appears to be devoid of such an effect, and finally that the ability of verapamil to decrease TPR may depend upon resting sympathetic tone.

Leukotriene C4 generation from human eosinophils stimulated with IgG-Aspergillus fumigatus antigen immune complexes

Sepharose beads coated with IgG stimulate eosinophils to produce leukotriene C4 (LTC4). This observation has been extended with specific immobilized IgG/antigen immune complexes to elicit mediator generation. An extract of Aspergillus fumigatus was covalently coupled to Sepharose beads and incubated with the IgG fraction of immune serum from patients with allergic bronchopulmonary aspergillosis. These beads elicited generation of 7.72 +/- 1.7 pmol of LTC4 immunoreactive material (n = 5) from 1 X 10(6) normal eosinophils of greater than 86% purity, and significantly less LTC4 (0.73 +/- 0.19 pmol per 10(6) cells; n = 3) was produced by eosinophils after incubation with beads treated with IgG from normal nonimmune serum. The maximum antibody-dependent release achieved represented approximately 20% of that induced by the calcium ionophore (A23187). LTC4 was measured by radioimmunoassay and validated by reverse-phase high-performance liquid chromatography. The amount of LTC4 generated was dependent on the concentration of A. fumigatus-specific IgG, and mediator release was completely abolished by prior adsorption of the IgG fraction onto Sepharose-protein A (Staphylococcus aureus). Grass pollen-specific IgG antibody/antigen complexes, in combination with Sepharose beads, also triggered generation of LTC4 immunoreactive material. There was no evidence to suggest that IgE/A. fumigatus immune complexes triggered LTC4 generation, although IgE myeloma protein, in association with Sepharose beads, was a weak stimulus. The efficacy of the IgG immune complex-dependent stimulation of eosinophils suggests a possible physiologic mechanism whereby these cells could participate in the inflammatory changes associated with allergic bronchopulmonary aspergillosis and similar allergic disorders.

Simultaneous determination of ventricular function and systemic hemodynamics in the conscious rat

This study describes a method that utilizes a combination of the Millar transducer and Columbus thermistor in the conscious, spontaneously hypertensive rat and that permits simultaneous evaluation of the effects of cardiovascular agents on ventricular performance and systemic hemodynamics. Left ventricular end diastolic pressure (LVEDP, mmHg) and LV dp/dt (mmHg/sec) were measured with a Millar transducer inserted into the left ventricle of spontaneously hypertensive rats under ether anesthesia. Cardiac output (CO, ml/min) was measured by thermodilution (Columbus Instruments) with a thermocouple in the thoracic aorta via the femoral artery. Mean arterial pressure (MAP, mmHg) was measured via a catheter in the other femoral artery. All cardiovascular parameters measured were shown to attain a steady state within 3 hr after cessation of ether administration. Infusion of the beta adrenergic receptor agonist isoproterenol increased LV max dP/dt, heart rate (HR), and CO, and decreased arterial blood pressure and peripheral resistance. Administration of propranolol resulted in decreased HR, LV dP/dt and CO. The results show that this model was stable over an extended period of time and was responsive to standard inotropic agents. Thus, the combined use of the Millar transducer and the Columbus thermistor appears suitable for the assessment of acute pharmacological interventions on cardiovascular function in the conscious rat.

Effects of nedocromil sodium (Tilade) on the activation of human eosinophils and neutrophils and the release of histamine from mast cells

The ability of nedocromil sodium, a new anti-inflammatory agent for the treatment of asthma, to inhibit activation of human eosinophils and neutrophils in vitro, has been studied using an adherence reaction (the "rosette" technique) as well as a cytotoxicity assay. We have also investigated the capacity of nedocromil sodium to inhibit IgE-dependent histamine release from human lung mast cells. The drug was a potent inhibitor (IC50 approx 5 x 10(-9)M) of fMLP-induced enhancement of eosinophil and neutrophil complement (C3b) and IgG (Fc) rosettes. There was also a comparable inhibition of enhancement, by fMLP, of eosinophil and neutrophil cytotoxicity (for complement-coated schistosomula of Schistosoma mansoni). Although nedocromil sodium also inhibited histamine release from human lung mast cells in a dose-dependent fashion its activity was relatively weak (IC30 5 x 10(-6)M) compared to its effect on granulocytes. These experiments support the view that the principal mode of action of nedocromil sodium is its capacity to inhibit the activation of inflammatory cells.

Cardiovascular effects of chronic high-dose atriopeptin III infusion in normotensive rats

Seventy-eight Sprague-Dawley rats received continuous intravenous infusions of either atriopeptin III (APIII), 60 micrograms/kg/hr, or distilled water vehicle for a period of 7 days by means of osmotic minipumps. On Day 7 approximately one-half of the animals (20 vehicle-treated rats and 21 APIII-treated rats) were instrumented for evaluation of cardiac function and terminated for measurement of heart weight. The minipumps remained in place during the evaluation of cardiac function. Also on Day 7, the osmotic pumps were removed from the remaining animals and an additional 7 days were allowed to elapse before heart weight and cardiac function were evaluated. Mean arterial blood pressure (MAP) of rats receiving APIII for 7 days was significantly lower (-9%, p less than 0.05) than that of rats receiving vehicle for 7 days. In addition, reductions (p less than 0.05) of total ventricular weightdry (-7%), left ventricular weightdry (-8%), and right ventricular weightdry (-9%) were observed in the APIII-treated rats (all ventricular weights are normalized for body weight). Hematocrit (HCT) was significantly higher (13%, p less than 0.05) in the APIII-treated group. Chronic APIII infusion did not influence ventricular performance nor did it affect regional vascular resistances. Seven days after termination of the APIII infusion the differences in MAP and HCT between vehicle-treated and APIII-treated animals were no longer evident. Partial recovery of the effect on heart weights was apparent, with total ventricular weightdry and left ventricular weightdry remaining slightly reduced (-4 and -5%, respectively; p less than 0.05). No differences were found between the two recovery groups for any index of cardiac function. In separate experiments, it was demonstrated that APIII, 60 micrograms/kg/hr iv, caused a significant increase in urine volume (p less than 0.05 relative to vehicle) during the initial 24 hr of infusion. The results indicate that chronic infusion of a large diuretic dose of APIII exerts relatively little influence on overall cardiovascular function in normotensive rats.

Chemotactic factor-induced low density neutrophils express enhanced complement (CR1 and CR3) receptors and increased complement-dependent cytotoxicity

We have studied chemotactic factor-induced 'complement receptor enhancement' to determine whether changes in receptor expression and complement-dependent cytotoxicity were associated with alterations in cell density. Ficoll-Paque separated normal human neutrophils (greater than 90%), when further fractionated on discontinuous metrizamide (MTZ) gradients (18, 19, 20, 21, 22, 23% MTZ), consistently gave two major bands at the 20/21% and 21/22% interfaces. Incubation with the synthetic chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine (fMLP (10(-8) M)), converted virtually all neutrophils to low density cells sedimenting on MTZ at the 18/19% and 19/20% interfaces. There was a time-dependent change of density after fMLP-stimulation which was maximal at 30 min, with cells reverting towards normal density by 60 min. Control unstimulated cells did not alter their density at any of the time points examined. Activated, low density neutrophils had increased expression of CR1 and CR3 (as shown by flow cytometry and the uptake of 125I-F(ab')2 monoclonal anti-CR1 antibody (E11)). These cells also showed enhanced cytotoxic capacity in vitro for helminthic targets (schistosomula of Schistosoma mansoni) opsonized with autologous complement. There were highly significant correlations between cell density and anti-CR1 uptake (P less than 0.001), and between schistosomular killing and change in density (P less than 0.001). Increased CR1 expression also correlated with enhanced helminthicidal capacity of neutrophils (P less than 0.001). Complement dependent cytotoxicity was partially reduced after treatment of cells with anti-human CR1 and/or CR3 antibodies, but only in the presence of a second antibody. These findings indicate that chemotactic factor-induced complement receptor enhancement of human neutrophils is associated with a decrease in cell density and increased complement-dependent cytotoxicity (CTX).

Enhanced potency dipeptide glycol renin inhibitors: studies in vitro and in the conscious rhesus

We prepared a series of novel dipeptide amides of the formula Boc-Phe-Leu-X, where X is a 3-amino-3-alkyl-1,2-propanediol with lower alkyl substitutions at C-1, in order to probe accessory binding sites in the enzyme renin. This approach was successful in generating potent inhibitors of human and hog renin in vitro. Moreover, these inhibitors were able to effect in vivo reduction of plasma renin activity (PRA) in the conscious salt-depleted rhesus monkey (i.v. route); this effect was related to the size of the C-1 alkyl group.

Leukotriene B4 generation by human neutrophils following IgG-dependent stimulation

It has previously been shown that human neutrophils generate substantial quantities of LTB4 when stimulated with the calcium ionophore, A23187, or with unopsonized zymosan. We now report that normal human neutrophils produced substantial quantities of LTB4 (measured by radioimmunoassay and validated by RP-HPLC) when incubated with large non-phagocytosable IgG-coated beads (Sepharose 4B). LTB4 was identified in both the extra and intracellular compartments. The production of LTB4 was dependent upon the number of IgG-coated particles and the concentration of IgG bound to the beads. Release was maximal after a 15-30 min incubation time and was enhanced by prior activation of the neutrophils with the synthetic bacterial product f-met-leu-phe. Comparable LTB4 production was also observed when neutrophils were incubated with antigen (Aspergillus fumigatus)-coated beads sensitized with purified IgG obtained from the sera of patients with allergic bronchopulmonary aspergillosis. These results suggest a further mechanism by which neutrophils may be activated to produce inflammatory mediators in the tissues.

Disodium cromoglycate inhibits activation of human inflammatory cells in vitro

Recent clinical studies indicate that disodium cromoglycate (DSCG) may have a direct effect on inflammatory cells because the drug reversed various changes in leukocyte function, such as increased membrane-receptor expression and enhanced cytotoxic capacity observed in peripheral white blood cells from subjects with asthma undergoing allergen-inhalation challenge. In the present study, we have demonstrated that DSCG, at low concentrations (a concentration of drug required to produce 50% inhibition, approximately 10(-8) mol/L) and in a time-dependent fashion, directly inhibited the activation in vitro of human neutrophils, eosinophils, and monocytes. Peripheral blood leukocytes were incubated with the synthetic chemoattractant, formyl-methionyl-leucyl-phenylalanine (at an optimal concentration of 10(-8) mol/L), and activation was assessed by measuring increases in the percentages of complement and IgG (Fc) rosettes as well as the enhanced capacity of these cells to kill target organisms (schistosomula of Schistosoma mansoni). DSCG at a concentration of 10(-7) mol/L totally inhibited both the formyl-methionyl-leucyl-phenylalanine-induced enhancement of complement and IgG rosettes, as well as increased schistosomular killing. These observations indicate that DSCG directly inhibits the secretory properties of inflammatory cells and that in turn might have important implications in modulating mechanisms contributing to the inflammatory component of asthma and allergic disease. It may also help to explain why compounds with considerably greater mast cell stabilizing properties than DSCG have been so disappointing when they are evaluated clinically.

Selective vasodilation produced by renal denervation in adult spontaneously hypertensive rats

The kidneys of adult male spontaneously hypertensive rats (SHR) were denervated, and systemic and regional blood flows were measured 3 to 5 hours or 5 days after denervation. Arterial pressure was reduced 20 to 27% in denervated SHR during both periods compared with that in sham-operated SHR (iliolumbar blood vessels painted with phenol). This hypotensive response was produced by a 32 to 35% reduction in total peripheral resistance. At 3 to 5 hours and at 5 days, a major decrease in total peripheral resistance was produced by vasodilation in the kidneys and splanchnic organs. Acute urine output, sodium excretion, and plasma renin activity in response to a saline load were not different between sham-operated and denervated SHR. The decreased total peripheral resistance in denervated SHR may have been secondary to a decreased central sympathetic nerve activity revealed by a decreased maximum response to ganglionic blockade. The results suggest that a pathophysiological link may exist between the kidneys and splanchnic organs in genetic hypertension and that specific efferent antiadrenergic or antiafferent nerve therapy, or both, in the kidney may lead to substantial specific decreases not only in renal vascular resistance but also in splanchnic vascular resistance and total peripheral resistance.

Enhancement of leukocyte cytotoxicity after exercise-induced asthma

We have previously shown that there were elevations of neutrophil chemotactic activity (NCA) and increases in the percentages of neutrophil and monocyte complement rosettes after exercise-induced asthma (EIA). These observations suggested that leukocyte activation may occur after EIA, possibly as a result of the release of mast-cell-associated mediators. In the present study, we have attempted to establish whether neutrophils and monocytes are functionally altered after EIA as assessed by changes in their cytotoxic capacity. Cytotoxicity was assessed by a direct visual killing assay using opsonized (complement-coated) schistosomula of Schistosoma mansoni as target organisms. Neutrophils and mononuclear cells obtained from 8 patients after exercise-induced asthma (EIA+ve) had increased cytotoxicity for opsonized schistosomula for as long as 60 min after exercise. These changes were preceded by elevations in the concentrations of serum high molecular weight NCA (which were maximal at 10 min after exercise). In asthmatic patients who did not develop exercise-induced asthma (EIA-ve), no significant increases in neutrophil or mononuclear cell killing of schistosomula, or serum NCA concentrations, were observed. There was a highly significant correlation (p less than 0.001) between the reduction in FEV1 and the increases in neutrophil cytotoxicity. In 5 EIA+ve patients, administration of disodium cromoglycate (cromolyn) prior to the exercise task inhibited both the enhancement in neutrophil and mononuclear cell cytotoxicity, as well as the elevations in circulating NCA and the reductions in FEV1.(ABSTRACT TRUNCATED AT 250 WORDS)

The requirements for transferrin-dependent adherence of human granulocytes to pollen grains

Human granulocyte/pollen binding protein (GPBP), previously identified as serum transferrin, promoted prolonged firm adherence of neutrophils to Timothy grass pollen. Some characteristics of this adherence reaction are reported. GPBP-induced binding was time-, temperature- and concentration-dependent. Maximal adherence was observed by 2 h and was only slightly decreased at 18 h. The optimal temperature for adherence was 37 degrees C. Concentrations of GPBP as low as 1.25 microgram/ml gave significantly greater binding than the albumin or lactoferrin control. Eosinophils, monocytes and lymphocytes did not appear to participate in GPBP-induced pollen binding reactions at concentrations up to 300 micrograms/ml. In the presence of GPBP, neutrophils adhered to a range of grass, weed and tree pollens. These included timothy, meadow, false oat, rye, giant and short ragweed, plantain, silver birch and ash. GPBP did not facilitate the adherence of granulocytes to inert particles of similar size such as Sephadex beads and agarose. The adherence was Mg++- but not Ca++-dependent and was not inhibited by a monoclonal antibody to the transferrin receptor (OKT9). Transferrin/GPBP did not bind to either neutrophils or pollen grains. A purified commercial transferrin reacted in all respects like GPBP in these pollen binding studies. These observations indicate that GPBP/transferrin-induced adherence of granulocytes to pollen grains is a hitherto unrecognized property of transferrin which appears unrelated to iron transport or the conventional transferrin receptor.

Binding of immunoglobulin classes and subclasses to human neutrophils and eosinophils

A comparative study of membrane expression of immunoglobin (Fc) receptors on human eosinophils and neutrophils has been undertaken using human IgG-1, IgG-2, IgG-3, IgG-4, IgA-1, IgA-2, IgM, IgD and IgE myeloma proteins. Sheep erythrocytes (E) coated with either human IgG-1, IgG-2, IgG-3 or IgG-4 myeloma proteins formed rosettes with human neutrophils and eosinophils. Proportionally more (1 1/2-2 times) rosettes were observed with neutrophils compared to eosinophils. In contrast, E-IgE bound to eosinophils (but not to neutrophils) to a degree that was comparable to E-IgG-1. Although IgG and IgE rosettes were inhibited by aggregates prepared from their corresponding myeloma protein there was no evidence that eosinophils and neutrophils have distinct receptors for IgG subclasses. Cells from four patients with hypereosinophilia were separated on density (metrizamide) gradients. The percentages of E-IgG-1 and E-IgE rosettes with normal- and light-density eosinophils were similar. Neutrophils, but not eosinophils, also bound significantly more E-IgA-1 and E-IgA-2 than the E-human albumin (E-Alb) control. In contrast, neutrophil and eosinophil rosette formation with E-IgM and E-IgD was not significantly different from E-Alb or E alone. These experiments indicate that human neutrophils and eosinophils bind homologous IgG subclass myeloma proteins, eosinophils, but not neutrophils, bind E-IgE with a similar avidity to that observed with E-IgG1, neutrophils, but not eosinophils, readily express demonstrable receptors for IgA-1 and IgA-2 and neither neutrophils nor eosinophils form E-IgM or E-IgD rosettes in greater numbers than the E-Alb controls.

Effect of disodium cromoglycate on activation of human eosinophils and neutrophils following reversed (anti-IgE) anaphylaxis

Immunological release of histamine and lipid mediators is known to occur when basophils, contained in whole blood human leucocytes, are incubated with anti-IgE (reversed anaphylaxis). In the present study we show that IgE-dependent stimulation of basophils was associated with activation of bystander eosinophils and neutrophils, as assessed by enhanced complement (C3b) and IgG (Fc) rosettes, and increased cytotoxicity for complement-coated schistosomula of Schistosoma mansoni. These changes in eosinophil and neutrophil function were totally inhibited in a dose-dependent fashion by prior incubation with disodium cromoglycate (DSCG). In all in vitro systems examined, complete inhibition of enhancement was observed with concentrations as low as 10(-7) moles/l. In contrast, DSCG had no effect on histamine release, or the percentage of rosettes or cytotoxicity prior to anti-IgE stimulation. These results suggest that DSCG inhibits activation of inflammatory cells consequent to an IgE-dependent stimulus.

Enhancement of human neutrophil complement receptors: a comparison of the rosette technique with the uptake of radio-labelled anti-CR1 monoclonal antibody

We have compared the rosette technique (using C3b-coated red cells) with the uptake of a 125I F(ab')2 anti-complement receptor type 1 (CR1) monoclonal antibody (E11) for studying the phenomenon of chemotactic factor (fMLP)-induced complement receptor enhancement (CRE) on human neutrophils. With both methods the dose responses of fMLP were similar with maximal CRE being observed at 10(-7) moles 1(-1). Conversely, the time course of CRE and the effects of disodium cromoglycate (DSCG) on inhibition of enhancement were discrepant. Maximal CRE with the rosette method was observed at 30 min, whereas increased uptake of anti-CR1 had still not reached a plateau after 1 h. DSCG inhibited fMLP-induced CRE, as assessed by the rosette technique, whereas this agent had no effect on increased binding of radio-labelled anti-CR1 antibody. These results suggest that in CRE the increased adherence of C3b-coated red cells to fMLP-stimulated neutrophils, as measured by the rosette technique, is not dependent exclusively on the increased numbers of CR1.

Dipeptide glycols: a new class of renin inhibitors

The discovery of a new class of novel renin inhibitors consisting of protected dipeptide amides derived from aminoglycols (Formula I) prompted a study of structure-activity in vitro and efficacy in vivo. Thus, Boc-L-Phe-N-[(1S,2R)-1-benzyl-(2,3-dihydroxy)propyl]-L-leucinamide (1) and the corresponding histidinamide (2) inhibit human renin in vitro (IC50: 8.7 X 10-6 M and 2.6 X 10-6 M, respectively). Compound 1 has a slight inhibitory effect on pepsin and compound 2 does not inhibit pepsin at all (at 10-4M); these compounds are inactive against rat renin. Compound 1 is efficacious in lowering plasma renin activity in the Rhesus monkey (i.v.). Results indicate that this new class of low molecular weight inhibitors is specific for human renin and thus constitutes a new source of drug candidates.

Activated human eosinophils generate SRS-A leukotrienes following IgG-dependent stimulation

Eosinophils, a class of granular leukocytes, are prominent in many inflammatory processes, particularly in asthma, certain allergic diseases and during infections with helminthic parasites. Following incubation with the Ca ionophore A23187 (refs 1-4) (a non-physiological agent which circumvents membrane calcium-gating mechanisms), eosinophils generate large amounts of sulphidopeptide leukotrienes, potent inducers of smooth muscle constriction and mucus production. These are now known to represent the activity previously termed 'slow-reacting substance of anaphylaxis' (SRS-A) but attempts to identify a physiological stimulus for SRS-A production by eosinophils have so far been unsuccessful. The cells contain recognized receptors for IgG (Fc) and it is known that they adhere to, and can be activated by, contact with the surface of large organisms such as helminthic larvae. We show here that eosinophils, particularly when activated, produce sulphidopeptide leukotrienes after contact with large particles coated with IgG.

Inhibition of leukotriene C4 and B4 generation by human eosinophils and neutrophils with the lipoxygenase pathway inhibitors U60257 and BW755C

Human eosinophils and neutrophils have the capacity to generate leukotriene C4 (LTC4) and leukotriene B4 (LTB4) respectively when stimulated by calcium ionophore A23187. Leukotriene production by mixtures of these cell types was measured by radioimmunoassay for LTC4 and LTB4, and the specificities of the assays determined by assessing cross-reactivities with a number of other arachidonic acid metabolites. The IC50S for LTC4 and LTB4 in their respective assays were 1.76 +/- 0.04 nmol and 3.00 +/- 0.08 nmol. Cross-reactivity for anti-LTC4 was shown by leukotriene D4 (LTD4) (70%) and leukotriene E4 (LTE4) (8%), when compared to LTC4, whereas in the radioimmunoassay for LTB4, only the 5(S), 12(R) 6-trans isomer of LTB4 showed appreciable interaction (12%). LTC4 production by eosinophil enriched cell fractions obtained from metrizamide gradients was inhibited in a dose-dependent fashion by the prostacyclin analogue, 6,9-deepoxy-6,9-phenylimino-delta 6,8-prostaglandin I, (U60257) and by 3-amino-1-(3-trifluoromethyl phenyl)-2-pyrazole (BW755C). The ID50 values for U60257 and BW755C were 2 X 10(-6) and 5 X 10(-6) M respectively. This demonstration of LTC4 production by human eosinophils, which are known to be important cells in clinical asthma, provides an in vitro model to assess 5-lipoxygenase inhibitors in human tissue.

Leukocyte activation in allergen-induced late-phase asthmatic reactions

Some patients with allergen-induced asthma have both an early and late reaction to allergen (dual asthmatic reactions). To investigate the role of leukocyte activation in dual asthmatic reactions, we measured neutrophil chemotactic activity, percentages of neutrophil and monocyte complement rosettes, and one-second forced expiratory volume (FEV1) in 11 patients with allergen-induced dual asthmatic reactions after a challenge with allergen. To control for the effects of bronchoconstriction, the same studies were done after a challenge with methacholine. In all subjects there was a biphasic increase in neutrophil chemotactic activity and the percentages of neutrophil and monocyte complement rosettes, accompanied by a reduction in the FEV1. After methacholine, there were no significant changes in neutrophil chemotactic activity or percentages of complement rosettes, despite bronchoconstriction. Six patients with single-phase allergen-induced asthma had similar responses, but they were monophasic. We conclude that allergen-induced early and late asthmatic reactions are accompanied by activation of leukocytes and that these alterations probably reflect the release of mediators from mast cells rather than an effect of bronchoconstriction.

Altered regional vasodilator responses to glossopharyngeal nerve stimulation in spontaneously hypertensive rats

The hindlimb and renal vasodilator responses produced by electrical stimulation of the glossopharyngeal nerve were examined in adult (six to eight months) male spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) normotensive rats to ascertain whether central neurogenically activated vasodilator capacity of these regional vascular beds is altered in SHR. Changes in systemic blood pressure and regional blood flow were simultaneously measured, and vascular resistance was calculated. Glossopharyngeal nerve stimulation (3.0 volts, 0.3 ms) at the frequency of 10 Hz resulted in a significantly greater vasodilation (% decrease in resistance) in SHR than in WKY control for both the hindlimb (SHR - 13.0 +/- 1.5% versus WKY - 3.4 +/- 1.6%, P less than 0.01) and renal (SHR - 7.6 +/- 0.6% versus WKY - 1.3 +/- 0.4%, P less than 0.01) vascular beds. The linear portion of the frequency-response curves of hindlimb or renal vasodilation of SHR was shifted parallel to the left of the WKY curve. Stimulus frequencies required to produce a 20% reduction in hindlimb resistance and a 10% reduction in renal resistance were lower in SHR (hindlimb 17.0 +/- 1.8 Hz; renal 19.9 +/- 1.4 Hz) than in WKY control (hindlimb 24.6 +/- 1.1 Hz; renal 39.3 +/- 4.8 Hz; P less than 0.01). The maximal vasodilator response to glossopharyngeal nerve stimulation in the hindlimb vascular bed was similar in SHR and WKY control, but in the renal vascular bed SHR showed a greater maximal response compared to WKY normotensives (SHR - 16.3 +/- 0.9% versus WKY - 12.7 +/- 1.6%, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Chemotactic factor-induced enhancement of the binding of human immunoglobulin classes and subclasses to neutrophils and eosinophils

Sheep erythrocytes (E) coated with either human IgG1, IgG2, IgG3 or IgG4 myeloma proteins formed rosettes with human neutrophils and eosinophils. Prior incubation with the chemotactic agents f-met-leu-phe or leukotriene B4 enhanced neutrophil and eosinophil E-IgG1 rosettes in a time- and dose-dependent fashion. There were comparable increases in neutrophil and eosinophil f-met-leu-phe-induced rosettes with either E-IgG1, E-IgG2, E-IgG3 or E-IgG4 whereas this agent did not appear to influence E-IgA1, E-IgD, E-IgM or E-IgE binding to these granulocytes. These studies indicate that human neutrophil and eosinophil IgG (Fc) receptors are enhanced by chemotactic agents in a similar way to that previously described for complement receptors.

Differential blocking effects of prazosin and yohimbine on vasopressor responses to sympathetic nerve stimulation and intravenous norepinephrine in the pithed rat

The effects of prazosin and yohimbine on the vasopressor response to sympathetic nerve stimulation, and to i.v. administration of norepinephrine were studied in the pithed rat to ascertain whether prazosin and yohimbine would preferentially block pressure responses due to exogenous versus endogenous alpha-adrenergic receptor activation. Prazosin (3 and 10 micrograms/kg, i.v.) was more effective in blocking the response due to sympathetic nerve stimulation than that due to i.v. norepinephrine. On the other hand, yohimbine (0.3 and 1 mg/kg, i.v.) produced greater inhibition of the i.v. norepinephrine response than the sympathetic nerve stimulation response. Yohimbine at the 0.1 mg/kg dose enhanced the nerve stimulation response while at higher doses the response was either unchanged (at 0.3 mg/kg) or substantially reduced (at 1 mg/kg). In this model, prazosin and yohimbine showed dose-related blocking effects on the pressor response of phenylephrine and clonidine, respectively. The results suggest that prazosin and yohimbine preferentially block the pressor responses of postsynaptic alpha-adrenergic receptor activation due to endogenous and exogenous norepinephrine, respectively. The diverse effects of yohimbine on the sympathetic nerve stimulation response may be due to an action on both the presynaptic (low dose) and postsynaptic (high dose) alpha-2 adrenergic receptors in vascular smooth muscle.

Systemic and regional haemodynamic effects of renal denervation in spontaneously hypertensive rats

Systemic and regional haemodynamic effects of renal denervation were evaluated in adult (six-month-old) male spontaneously hypertensive rats (SHR) using the Fick procedure and electromagnetic flowmetry technique. Renal denervation (bilateral, 10% phenol in ethanol), performed five to eight days before the experiment, resulted in a significant decrease (-12%) in arterial pressure in conscious SHR (denervated = 182 +/- 4 versus sham = 207 +/- 8 mmHg, P less than 0.05) that was associated with a reduction in total peripheral resistance (TPR: denervated = 1.83 +/- 0.19 versus sham = 2.78 +/- 0.29 mmHg/ml/min, P less than 0.05) and an increase in cardiac output (denervated = 106 +/- 10 versus sham = 80 +/- 9 ml/min, P less than 0.05). Heart rate was not different between the two groups. Renal, hindquarter and superior mesenteric blood flows, determined under pentobarbital anaesthesia, of denervated SHR were not significantly different from sham values. Renal vascular resistance (mmHg/ml/min) was substantially reduced (-39%) in the denervated SHR (denervated = 25.1 +/- 1.86 versus sham = 41.1 +/- 3.48, P less than 0.01), but vascular resistances in the hindquarter and superior mesenteric beds were not reduced significantly. In this preparation TPR was reduced 32% in denervated SHR. The data demonstrate that renal denervation in adult SHR proves an antihypertensive vasodilator-like effect related to a decrease in TPR with increased cardiac output. The reduction in renal vascular resistance in denervated SHR may produce a major contribution to decreased TPR. Other beds may also contribute to the decrease in TPR, although to a lesser extent, since the decrease in TPR cannot be fully accounted for by decreased renal vascular resistance.

Complement receptor enhancement as evidence of neutrophil activation after exercise-induced asthma

To determine whether neutrophils are activated after exercise-induced asthma, increases in neutrophil complement receptor numbers (complement receptor enhancement) were measured by the rosette technique. In twelve asthmatic patients there was a time-dependent rise in complement receptor numbers for up to 60 min after treadmill exercise. This enhancement of complement receptors was preceded by a rise in plasma neutrophil chemotactic activity and a reduction in the peak expiratory flow rate. These changes could be inhibited by prior administration of disodium cromoglycate. The changes were not observed in seven asthmatic patients in whom asthma was not induced by an identical exercise task. Complement receptor enhancement was also observed in vitro when partially purified neutrophil chemotactic activity from a patient with exercise-induced asthma was incubated with normal neutrophils. These findings suggest that inflammatory cells are activated after exercise-induced asthma, possibly as a result of the release of neutrophil chemotactic activity and other mast-cell-associated mediators.

Increased systemic vascular responsiveness to catecholamines in spontaneously hypertensive rats

Systemic vascular responsiveness to i.v. bolus injections of norepinephrine and tyramine was evaluated in adult male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Changes in total peripheral resistance (TPR) were used as an index of vascular response. Dose-response curves were plotted with 1n-dose on the x-axis and percent of maximum change in TPR on the y-axis, and the following indices of responsiveness were used: slope, 1nED50, 1nx-intercept, and maximum response. Measurements were made before and after ganglionic blockade with pentolinium (5 mg/kg, i.v.). Cardiac output for TPR calculations was obtained from an implanted flow probe on the ascending aorta. The slopes and maximum responses to norepinephrine and tyramine were greater in SHR v. WKY, P less than .05, before and after pentolinium treatment. There were no significant differences in 1nED50 or 1nx-intercept between WKY and SHR for tyramine and norepinephrine prior to pentolinium. After pentolinium 1nED50 and 1nx-intercept were similar for SHR and WKY for norepinephrine, but were greater in SHR for tyramine. The results demonstrate an increased systemic vascular responsiveness to catecholamines in adult SHR, with no evidence of increased systemic vascular sensitivity. These findings are consistent with the concept of increased systemic vascular responsiveness to catecholamines in adult SHR secondary to structural changes in blood vessels.

Vascular pressure-flow analysis in normal and hypoxemic spontaneously hypertensive rats

The pressure-flow relationship of the autoperfused subclavian vascular bed was compared in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) after spinal cord transection. Studies were performed under normoxemic and hypoxemic conditions. In adult SHR, vascular resistance was greater relative to WKY under both conditions. In young (8 week old) SHR vascular resistance was consistently greater over a wide range of perfusion pressures compared to young WKY rats when blood oxygen content was normal. Vascular resistance was not different between young SHR and WKY when the animals were hypoxemic. The results demonstrated that elevated vascular resistance in adult SHR was independent of oxygen availability and supraspinal nerve function; however, in young SHR elevated vascular resistance was dependent upon oxygen availability, although independent of supraspinal nerve function.

Unaltered maximum reflex vasodilatory capacity of the perfused hindquarters of spontaneously hypertensive rats

Hindquarter reflex vasodilation (RVD delta mmHg decrease in perfusion pressure) in response to arterial pressure elevations by intravenous norepinephrine (NE) was examined in young (2 1/2-3 months) and mature (8-10 months) spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) normotensive rats to ascertain whether maximum reflex vasodilatory capacity is altered in the developmental and/or established stages of spontaneous hypertension. The maximal RVD was not significantly different in young or mature SHR (young 26.2 +/- 1.9 and mature 36.2 +/- 3.2) compared to age-matched WKY controls (young 23.9 +/- 1.8 and mature 29.6 +/- 2.3) (P greater than 0.05 between SHR vs. WKY at both ages). However, the rise in mean systemic arterial pressure by NE which produced maximal RVD was greater in mature SHR (116.0 +/- 7.4 mmHg) than in WKY controls (78.3 +/- 6.2 mmHg) (P less than 0.01), whereas no such differences were found between young SHR (85.1 +/- 6.5 mmHg) and its WKY controls (87.5 +/- 2.3 mmHg). There was no difference in the dose of NE that required maximal responses of reflex vasodilation in young or mature SHR compared to WKY controls. In each age group of SHR or WKY rats, RVD was linearly related to the arterial pressure increments. The slope (a +/- SEM) of the regression line for the correlation between the pressure rises and resultant RVD was similar in young SHR (a = 0.424 +/- 0.061) and WKY controls of (a = 0.458 +/- 0.013). In contrast, the slope of the regression line for these two parameters in mature SHR (a = 0.250 +/- 0.004) was significantly smaller than that of either WKY controls (a = 0.364 +/- 0.010) or young SHR (P less than 0.01). The direct hindquarter vasodilation of mature SHR in response to intra-arterial administration of histamine or nitroglycerin was not different compared to that of WKY controls. The results indicate an unaltered maximum hindquarter reflex vasodilatory capacity during the developmental and established stages of genetic hypertension in SHR. An additional finding in the present study was the abnormal responsiveness of the baroreceptor reflex vasodilator system of mature SHR to a wide range of arterial pressure elevations. This abnormal responsiveness may contribute to the maintenance of high blood pressure in the established stage of hypertension.

Reflex cardiovascular responses induced by electrical stimulation of glossopharyngeal nerves in the rat

Reflex cardiovascular responses to electrical stimulation of glossopharyngeal nerves (GPN) were studied in Dial-Urethane anesthetized rats. GPN stimulation at 3 V, 0.3 msec and 50 Hz produced maximal reflex depressor (34 +/- 2 mmHg) and bradycardia (21 +/- 2 beats/min) responses that were altered as follows: pentolinium (0.25 mg/kg, i.a.) blocked approximately 72% and 89% of control values of depressor and bradycardia responses, respectively; tripelennamine (5 mg/kg, i.a.) significantly reduced depressor responses (76%); whereas atropine (0.4 mg/kg i.a.) blocked only bradycardia (85%). Regional blood flow studies showed that GPN stimulation reduced systemic arterial pressure (approximately 25%), and increased iliac artery blood flow (5%), and decreased blood flow through the renal (14%) and superior mesenteric (13%) arteries. Hence, decreases in vascular resistance during GPN stimulation were greater in the hindlimb vascular bed (28%) than in the renal (14%) or the mesenteric vasculatures. In addition, the magnitude of decreases in hindlimb vascular resistance by GPN stimulation was reduced (80%) by pretreatment with tripelennamine, but not by atropine. The results suggest that reductions in arterial blood pressure and hindlimb vascular resistance of the rat in response to GPN stimulation may be mediated via a histaminergic vasodilator mechanism, and that there may be a differential pattern of reflex vascular adjustments of blood flow and vascular resistance among regional vasculatures of the rate.

Hemodynamic and metabolic responses to repeated blood sampling in the rat

Repeated blood sampling (0.2 ml) in the conscious rat during the course of 10 cardiac index measurements using the Fick procedure did not alter the cardiac index as measured initially (285 ml x min-1 x kg-1). However, oxygen consumption and hematocrit were reduced 7-19% and 4-14%, respectively. Replacement of blood removed during sampling with donor blood prevented these responses, but also led to reduced cardiac index and arterial oxygen content, 22-28% and 10-21%, respectively. In additional studies in anesthetized rats, hemorrhage (25 ml/kg) increased plasma K+ by 29% and reduced plasma Na+ by 3%, suggesting that compensatory fluid replacement originated in cells as well as interstitium. This fluid replacement after blood loss helps sustain normal systemic hemodynamics, but blood loss can produce metabolic alterations that should be taken into account in any biochemical study. Although metabolic alterations can be prevented by replacing lost blood with donor blood, cardiopulmonary function may be adversely affected.

Altered cardiovascular responses to glossopharyngeal nerve stimulation in the spontaneously hypertensive rat

Alterations in arterial blood pressure and heart rate in response to electrical stimulation of glossopharyngeal nerve (GPN) were examined in 6-10 months old, male spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) normotensive rats. GPN stimulation resulted in frequency-dependent decreases in arterial blood pressure in both SHR and WKY rats. SHR were more sensitive to GPN stimulation than WKY controls. Vasodepressor responses to GPN stimulation were greater in SHR than in WKY rats over a wide range of stimulus frequencies. At the frequency which produced the maximum response (50 Hz) the vasodepressor response was 68% greater in SHR than in WKY control. The results, indicate that neurogenically-induced vasodepression is enhanced in SHR, suggesting that decreased vasodepressor capacity mediated through the central nervous system is not involved in the maintenance of elevated blood pressure in SHR. In contrast to increased vasodepressor responses in SHR, GPN stimulation produced less bradycardia in SHR than it did in WKY rats. This difference may be central in origin because peripheral vagal stimulation produced essentially equal bradycardia in SHR and WKY normotensives.