Regulation of human eosinophil degranulation and activation by endogenous phospholipase A2.

The unique granular proteins of eosinophils may have a pathogenetic role in asthma and in the defense against parasitic infestations. However, the mechanisms regulating eosinophil degranulation are largely unknown. We examined the hypothesis that release of these proteins is regulated by endogenous activation of phospholipase A2. Human eosinophils (HE) were isolated from the peripheral blood of 42 subjects either by Percoll density separation or by negative-selection immunomagnetic fractionation. Eosinophil activation was initiated in vitro with 10(-6) M FMLP and 5 micrograms/ml cytochalasin B and was assessed by measurement of eosinophil peroxidase (EPO), leukotriene C4 (LTC4) and superoxide radical (.O2-) secretion. Treatment of HE with 100 microM mepacrine before activation blocked EPO release (2.0 +/- 0.2 vs 10.2 +/- 2.1% cell content for activated HE, P < 0.004, n = 9), .O2- generation (2.6 +/- 0.9 vs 44.2 +/- 10.8 nmol/ml per 10(6) HE, P < 0.002, n = 5), and LTC4 secretion (68.2 +/- 32.2 vs 1,125.2 +/- 526.8 pg/ml per 10(6) HE, P < 0.04, n = 8). Pretreatment of HE with 100 microM 4-bromophenacyl bromide before activation similarly blocked EPO release, .O2- generation and LTC4 secretion. Addition of AA to HE after treatment with 100 microM mepacrine and before subsequent activation reversed the inhibition of both EPO (10.4 +/- 2.2% with 1 microM AA vs 2.0 +/- 0.2% for mepacrine, n = 5, P < 0.02) and LTC4 secretion (695.1 +/- 412.9 with 10 microM AA vs 68.2 +/- 32.2 pg/ml per 10(6) HE for mepacrine, n = 8, P < 0.04), but did not reverse inhibition of .O2- generation by mepacrine. We demonstrate that secretion of preformed cytotoxic proteins and .O2- by eosinophils is regulated endogenously by phospholipase A2.

A kinetic assay for eosinophil peroxidase activity in eosinophils and eosinophil conditioned media.

The activity of eosinophil peroxidase (EPO) is commonly employed as a measure of eosinophil activation in biologic fluids. Determination of product formation by this enzyme by end-point measurement may be affected profoundly by substrate concentrations, reaction time and degradation of end-product and enzyme. To determine more accurately EPO concentrations in media conditioned by isolated, purified eosinophils, we have developed a kinetic, colorimetric assay to measure EPO concentration as a function of maximum velocity of reaction (Vmax). An automated method for determining Vmax in a 96-well microplate colorimetric assay was utilized over a wide range of substrate concentrations. Concentrations greater than or equal to 3 x 10(-8) g/ml could be determined reliably with this assay. Peroxidase activity was inhibited in a concentration-dependent manner by the addition of 3-amino-1,2,4-triazole (AMT). The EPO concentration in eosinophils determined by this kinetic method was approximately 1.1 x 10(-5) g/10(6) eosinophils. Eosinophil activation with 10(-6) M f-Met-Leu-Phe (fMLP) caused substantial EPO secretion (9.0 +/- 1.7% vs. 2.9 +/- 0.6% total EPO content for control, P = 0.05) and decrease in eosinophil EPO concentration (92.3 +/- 4.2% of control, P = 0.038). Secretion was enhanced by the addition of 5 micrograms/ml cytochalasin B to 10(-6) M fMLP (25.9 +/- 12.7% total EPO content, P = 0.043 vs. control); similar decreases were noted in eosinophil EPO concentration (71.7 +/- 16.1% of control, P = 0.043). These data demonstrate that determination of EPO secretion by measurement of Vmax is a reliable, accurate method for precise quantification of this enzyme in media containing purified eosinophils or eosinophil products in the absence of other forms of peroxidase activity.

Effect of cobalt protoporphyrin on hepatic drug-metabolizing enzymes. Specificity for cytochrome P-450.

Cobaltic protoporphyrin IX (cobalt protoporphyrin) is known to cause an extensive and long-lasting depletion of hepatic cytochrome P-450 in rats, and it has been used to evaluate the role of hepatic cytochrome P-450 in xenobiotic metabolism and toxicity. To examine the specificity of cobalt protoporphyrin for hepatic cytochrome P-450, cobalt protoporphyrin was administered to rats and hamsters, and its effects on cytochrome P-450-dependent and non-P-450-dependent phase I and phase II metabolism were determined. Cobalt protoporphyrin pretreatment depleted hepatic cytochrome P-450 in both species and lowered their Vmax values for the hepatic microsomal metabolism of ethylmorphine, aminopyrine, ethoxyresorufin and ethoxycoumarin, without change in their Km values. In the rat, cobalt protoporphyrin treatment lowered both the Vmax and Km for microsomal metabolism of aniline. In vivo hepatic cytochrome P-450-dependent metabolism, as measured by antipyrine clearance, was decreased in both species. UDP-Glucuronyltransferase, phenolsulfotransferase and glutathione-S-transferase were unaffected, as was hepatic glutathione. Modest effects of cobalt protoporphyrin were seen on the hepatic microsomal flavoprotein mixed-function oxidase (hamster only), cytochrome P-450 reductase, cytochrome b5 (rat only), UDPGA (rat only), and glycogen, and on blood glucose (rat). In in vivo studies with hamsters given a low dose of acetaminophen, cobalt protoporphyrin suppressed the apparent rate constants for the cytochrome P-450-dependent pathways of acetaminophen metabolism but had no effect on acetaminophen glucuronidation and sulfation. Polyacrylamide gel electrophoresis analysis indicated that cobalt protoporphyrin markedly reduced the levels of the cytochrome P-450 holoenzyme but did not alter either the content or profile of the cytochrome P-450 apoenzyme. collectively, the data indicate that cobalt protoporphyrin shows relatively high selectivity for the hepatic cytochrome P-450 system, and support the use of this compound as a tool for resolution of the role of hepatic cytochrome P-450 in xenobiotic metabolism and toxicity.

Effect of age on leukotriene B4 production in guinea pig whole blood.

We evaluated the effect of age on eicosanoid production in guinea pig blood. Heparinized blood from 7-10-day, 6-week, or 6-month-old guinea pigs was incubated with 150 microM arachidonic acid (AA) for 5 min, followed by stimulation with A23187 (20 micrograms/mL) for an additional 10 min at 37 degrees. The reaction was terminated by centrifugation, and the production of plasma leukotriene (LT) B4 and C4, prostaglandin E2 (PGE2), and thromboxane B2 (TXB2) was determined by enzyme-linked immunoassay (ELISA). LTC4, PGE2, and TXB2 formation were unaffected by age. In marked contrast, production of LTB4 was increased 4- to 5-fold as age increased from 7-10 days (9.51 +/- 2.07 ng/mL) or 6 weeks (8.83 +/- 1.81 ng/mL) to 6 months (40.57 +/- 9.66 ng/mL). To determine the effect of age on the total eicosanoid product profile, blood was stimulated in the presence of [14C]AA, and plasma metabolites were separated by reverse-phase high pressure liquid chromatography (RP-HPLC) and quantitated using on-line radiochemical detection. In addition to increased LTB4 production, a modest increase in 12-hydroxyeicosatetraenoic acid (12-HETE) production was also observed in the 6-month-old animals. Previous studies have demonstrated interference of 12-HETE in the immunoassay of LTB4. Therefore, to validate the authenticity of the plasma leukotriene ELISA measurements, samples were precipitated with methanol and fractionated by RP-HPLC. The fractions co-eluting with [3H]LTB4 or [3H]LTC4 were dried under vacuum and reconstituted in ELISA buffer, and leukotrienes were quantitated. As seen previously, following HPLC purification LTB4 production remained significantly elevated in the 6-month-old guinea pigs, whereas LTC4 production was unaffected by age. To further document the selectivity of this effect on LTB4 production, we evaluated the effect of increasing age on cyclooxygenase or phospholipase A2 (PLA2) activity. Neither cyclooxygenase nor PLA2 activity was elevated as animals matured. In conclusion, the capacity of whole blood to produce LTB4, but not LTC4, TXB2, or PGE2, was elevated markedly in older animals.

Guinea pig whole blood 5-lipoxygenase assay: utility in the assessment of potential 5-lipoxygenase inhibitors.

Guinea pigs are widely used in the study of the role of leukotrienes in airway pathophysiology. Extensive research efforts have utilized this species in the development of potential therapeutic agents associated with inhibition of leukotriene production (e.g. 5-lipoxygenase inhibitors and 5-lipoxygenase-activating protein antagonists) for the treatment of acute bronchospasm in asthma. We now report, for the first time, an ex vivo whole blood 5-lipoxygenase assay in guinea pigs which should prove useful in the future development of leukotriene biosynthesis inhibitors. Addition of 150 microM arachidonic acid (AA) to heparinized whole blood for 5 min prior to the stimulation with 20 micrograms/mL A23187 resulted in a 10-fold increase in leukotriene B4 (LTB4; 11.36 +/- 1.55 ng/mL) above basal (0.96 +/- 0.29 ng/mL) within 10 min. To further validate the utility of the assay, we utilized the 5-lipoxygenase inhibitor BW A4C. Pretreatment of guinea pig whole blood with BW A4C in vitro prior to stimulation resulted in a concentration-dependent inhibition of LTB4 production (IC50 = 229 nM), whereas thromboxane B2 (TXB2) production was unaffected. Likewise, when BW A4C was administered to guinea pigs intravenously (3 mg/kg), we observed a rapid and marked (approximately 90%) reduction in whole blood LTB4 production which returned to control (pre-drug values) by 5 hr. In contrast, TXB2 production was unaffected over the same experimental time period. In summary, we have described a whole blood assay which can discriminate 5-lipoxygenase inhibitors both in vitro and in vivo. Furthermore, this assay system will be of use in determining the potency, efficacy, selectivity, and pharmacodynamic properties of 5-lipoxygenase inhibitors in guinea pigs.

Contributory role of lung pleura to release of anaphylactic mediators from guinea pig lung in response to ovalbumin or A23187.

Previous findings revealed greater contractile responses of guinea pig lung pleural surface strips to antigen or A23187 challenge than denuded lung parenchymal strips (lung strip devoid of any pleura). Moreover, we have identified a high density of mast cells distributed throughout the lung pleura. The present study examined mediators released from guinea pig lung pleural surface and denuded lung parenchyma fragments in response to immunologic challenge with ovalbumin (OA) or non-immunologic challenge with the ionophore A23187. Histamine levels were measured radioenzymatically; leukotrienes (LTs), prostaglandins (PGs) and thromboxane B2 (TXB2), a stable metabolite of thromboxane A2 (TXA2), were quantitated using an enzyme immunoassay. Histamine release reached a maximal level 3-5 min after OA challenge, whereas A23187-induced histamine release increased gradually in a time-dependent manner. Similar kinetics were observed in the release of LTs, PGs and TXA2. Pleural surface released a substantially (P < 0.05) greater amount of histamine to both challenges than denuded parenchyma. Moreover, histamine content in pleural surface was significantly (P < 0.05) higher than in denuded parenchyma. Pleural surface also released considerably (P < 0.05) more LTB4, LTC4, and LTE4 in response to OA and A23187 than denuded parenchyma. In contrast, pleural surface and denuded parenchyma released equivalent amounts of PGD2, PGE2, PGF2 alpha, and TXA2 in response to both challenges. The rank order of leukotriene release was LTC4 > LTE4 > LTB4, whereas that of prostanoid release was TXA2 >> PGD2 > or = PGF2 alpha >> PGE2. We conclude that pleural surface is the major source of histamine and leukotrienes released from guinea pig lung in vitro in response to OA and A23187, whereas both pleural surface and denuded parenchyma participate to the same extent in prostaglandin and TXA2 production after such challenges.

Blockade of human neutrophil activation by 2-[2-propyl-3-[3-[2-ethyl-4-(4-fluorophenyl)-5- hydroxyphenoxy]propoxy]phenoxy]benzoic acid (LY293111), a novel leukotriene B4 receptor antagonist.

Leukotriene B4 (LTB4), a naturally occurring pro-inflammatory product of arachidonic acid metabolism, has been associated with human inflammatory disease. This study compares the abilities of two LTB4 receptor antagonists, 2-[2-propyl-3-[3-[2-ethyl-4-(4-fluorophenyl)-5-hydroxyphenoxy]- propoxy]phenoxy]benzoic acid (LY293111) and 7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]- 3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid (SC-41930), to displace LTB4 binding and their functional blockade of human neutrophil activation. LY293111 inhibited the binding of [3H]LTB4 with a Ki of 25 nM; SC-41930 displayed a similar potency (Ki = 17 nM). In contrast, LY293111 prevented LTB4-induced calcium mobilization with an IC50 = 20 nM, or 40 times more effectively than SC-41930 (IC50 = 808 nM). LY293111 was 300 times more potent than SC-41930 in blocking LTB4-induced CD11b up-regulation on isolated neutrophils. LY293111 also arrested LTB4-induced up-regulation of CD11b on neutrophils in whole human blood. LY293111 was not effective in blocking human neutrophil activation responses induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP), platelet-activating factor (PAF), human recombinant endothelial interleukin-8 (IL-8) or human recombinant complement component 5a (C5a).

The regulation of CD11b integrin levels on human blood leukocytes and leukotriene B4-stimulated skin by a specific leukotriene B4 receptor antagonist (LY293111).

CD11b is part of the beta2-integrin Mac-1 and plays an important role in neutrophil adhesion. Leukotriene B4 (LTB4) is an active upregulator of neutrophil CD11b-expression, acts as a potent chemoattractant to neutrophils and is also known to upmodulate epidermal proliferation. We performed a placebo-controlled study on LY293111, an oral LTB4 receptor antagonist. Twenty healthy male volunteers were randomised over three treatment groups that received placebo, 48 mg, or 200 mg drug twice daily for 10 days. Before and after treatment, flow cytometrical CD11b assessment was performed on in vitro LTB4-stimulated peripheral blood neutrophils. Additionally, skin biopsies were taken at 24 and 72 h after epicutaneous LTB4 application, before and after treatment. The effects on skin were assessed immunohistochemically using various markers. All observed effects were dose related. CD11b upregulation on blood neutrophils was significantly suppressed in both treatment groups compared to placebo. In skin, a significant suppression of inflammation and hyperproliferation occurred. Pronounced inhibition was observed on neutrophil migration into the epidermis and the inflammatory infiltrate was decreased. A similar but weaker response was seen in the dermis. The number of cycling cells as well as suprabasal keratin-16 expression were decreased in both treatment groups. LY293111 proved to be a potent inhibitor of LTB4-induced cutaneous inflammation and hyperproliferation. The potent antiinflammatory effect in vivo and the fact that in the present study the compound showed no clinically significant side effects make it an interesting drug in the future treatment of inflammatory conditions predominated by neutrophils.

Role of eicosanoids in hyperpnea-induced airway responses in guinea pigs.

Guinea pigs mechanically hyperventilated with dry gas exhibit hyperpnea-induced bronchoconstriction (HIB) and hyperpnea-induced bronchovascular hyperpermeability (HIBVH). Tachykinins released from airway C-fiber neurons are the central mediators of guinea pig HIB but play only a contributory role in HIBVH. Recent studies suggest that eicosanoid mediators can provoke bronchoconstriction and bronchovascular hyperpermeability, are released by dry gas hyperpnea, and can themselves elicit or modulate tachykinin release. We therefore hypothesized that eicosanoids may participate in HIB and/or HIBVH. To test these hypotheses, we analyzed respiratory system resistance changes and Evans blue-labeled albumin extravasation into the airways of 60 tracheostomized and mechanically ventilated guinea pigs. Animals were subjected to 10 min of isocapnic dry gas hyperpnea or to quiet breathing of humidified gas and received as pretreatment either piroxicam, a cyclooxygenase (CO) inhibitor; A-63162, a 5-lipoxygenase (5-LO) inhibitor; BW-755c, a combined CO and 5-LO inhibitor; ICI-198,615, a leukotriene D4 receptor antagonist; or no drug. HIB was substantially (50-80%) reduced by each of the four eicosanoid-modulating drugs. In contrast, HIBVH was reduced only by BW-755c, and this effect occurred only within the extrapulmonary airways (42% reduction). These data indicate that both CO and 5-LO products, including leukotriene D4, participate in the pathogenesis of HIB but that, like tachykinins, they play only a small contributory role in HIBVH. Together with our previous demonstration that sensory neuropeptide release is critical for the occurrence of HIB, we conclude that the roles of eicosanoids and tachykinins in guinea pig HIB are interdependent.

Flow cytometric evaluation of the effects of leukotriene B4 receptor antagonists (LY255283 and SC-41930) on calcium mobilization and integrin expression of activated human neutrophils.

Leukotriene B4 (LTB4) is a naturally occurring eicosanoid mediator which chemoattracts and stimulates human neutrophils to an activated state. In an attempt to identify novel antiinflammatory drugs, synthetic LTB4 receptor antagonists have been developed in several laboratories. In this study, the effects of two such LTB4 receptor antagonists were examined for their influences on two elements of human neutrophil activation using flow cytometric techniques. Quantitative flow cytometric assays of human neutrophil intracellular calcium mobilization and up-regulation of integrin (CD11b/CD18) cell surface expression were developed and used to determine the potency and selectivity of compounds LY255283 and SC-41930 on these activities. Our results indicate that both compounds preferentially block these functions of LTB4-induced human neutrophil activation in a concentration dependent manner and fall in the 1-2 microM range of antagonist activity. Compound SC-41930 was approximately twice as potent as LY255283 in blocking the targeted agonist effects. Both compounds were approximately 100-fold less potent in blocking the same functions of interleukin-8-induced human neutrophil activation.

Effects of two leukotriene B4 (LTB4) receptor antagonists (LY255283 and SC-41930) on LTB4-induced human neutrophil adhesion and superoxide production.

Leukotriene B4 (LTB4) induces a number of functional changes in human neutrophils, including both superoxide release and CD11b/CD18 (Mo1)-mediated adherence to various substrates, such as keyhole limpet hemocyanin (KLH). These effects are both time- and concentration-dependent. Neutrophil adhesion was at least 10-fold more sensitive to the stimulatory action of LTB4 than superoxide production. Two LTB4 receptor antagonists, LY255283 (1-(5-ethyl-2-hydroxy-4-(6-methyl-6-(1H-tetrazol-5-yl)heptyloxy )- phenyl)ethanone) and the sodium salt of SC-41930 (7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8- propyl-2H- 1-benzopyran-2-carboxylic acid) were evaluated for effects on human neutrophil superoxide production and adhesion. Despite being more sensitive to LTB4-induced stimulation, neutrophil adhesion was at least 100-fold less sensitive to inhibition by LY255283 and SC-41930 than superoxide production. Both LTB4 receptor antagonists behaved similarly in these models. These compounds did not inhibit neutrophil responses induced by granulocyte/macrophage colony-stimulating factor (GM-CSF).

Pulmonary actions of LY255283, a leukotriene B4 receptor antagonist.

The actions of LY255283, a leukotriene (LT) B4 receptor antagonist, were examined on guinea pig lung. LTB4 and LY255283 displaced [3H]LTB4 from its binding site on lung membranes with pKi values of 9.9 and 7.0, respectively. In the functional correlate of the binding studies, LY255283 competitively reduced contractile responses of lung parenchyma to LTB4 (pA2 = 7.2). LTB4 produced airway obstruction which was reduced by LY255283 administered i.v. (ED50 = 2.8 mg/kg) or orally (ED50 = 11.0 mg/kg). Contractile responses to histamine, LTD4 and the thromboxane mimetic, U46619, were not reduced by LY255283. The compound also did not inhibit cyclooxygenase or 5-lipoxygenase enzymes. We conclude that LY255283 selectively antagonized pharmacologic responses to LTB4 on lung tissue and appears to be a useful tool to investigate the role of LTB4 in pulmonary disease.

Contraction of guinea pig inferior vena cava by eicosanoids.

Guinea pig inferior vena cava contracted in response to leukotriene (LT)C4, LTD4, LTE4 U46619, phenylephrine, histamine, and KCl. Although LTC4, LTD4, and U46619 were the most potent agonists, active tension generated by these eicosanoids was only about half that of histamine or KCl. LTE4 and phenylephrine were marginally active. Biochemical analysis showed vena cava able to convert about 23% LTC4 to LTD4 and LTE4 in 45 min. Pretreatment with acivicin prevented this by abrogating conversion of LTC4 to LTD4. A subthreshold concentration of LTE4 reduced responses to LTC4 and LTD4. LY171883 and WY-48252 competitively antagonized LTD4-induced contractions of vena cava. In contrast, these antagonists blocked contractions to LTC4 in a biphasic manner. Lower segments of the LTC4 concentration-response curves were less affected than the upper portion suggesting the possibility of 2 LTC4 receptor subtypes. Our results indicate that LTE4 is a weak or partial agonist in this tissue and furthermore they suggest a lack of high affinity receptors for LTE4 favoring LTC4 and LTD4. Indomethacin did not influence contractions to the leukotrienes or histamine. However, the response to U46619 was greatly enhanced suggesting release of a vasodilator prostaglandin as part of the overall response of the vena cava to the thromboxane A2 mimetic.

Pharmacologic actions of the second generation leukotriene B4 receptor antagonist LY29311: in vivo pulmonary studies.

We examined the in vivo actions of LY293111 sodium (2-[2-propyl-3-[3-[2-ethyl-4-(4-fluorophenyl)-5-hydroxyphenoxy]pro poxy]phenoxy] benzoic acid sodium salt). Guinea pigs were used to evaluate the effect of this agent on (1) acute airway obstruction produced by intravenous leukotriene B4, (2) pulmonary granulocyte infiltration and delayed onset airway obstruction resulting from a 4-h leukotriene B4 inhalation and (3) lung inflammation after aerosol challenge with the divalent cationic ionophore A23187 (6S-[6alpha(2S*,3S*),8beta(R*),9beta,11alpha]-5- (methylamino)-2-[[3,9,11-trimethyl-8-[1-methyl-2-oxo-2-(1H-pyrrol-2-yl)e thyl]-1,7-dioxaspiro[5.5]undec-2-yl]methyl]-4-benzoxazole carboxylic acid). Airway obstruction was quantitated using pulmonary gas trapping measurements and lung inflammation was evaluated by bronchoalveolar lavage (BAL) and histology. LY293111 sodium produced a dose-related inhibition of acute leukotriene B4-induced airway obstruction when administered i.v. (ED50=14 microg/kg) or p.o. (ED50=0.4 mg/kg). In contrast, LY293111 sodium did not inhibit the pulmonary gas trapping caused by aerosols of histamine, leukotriene D4, or the thromboxane mimetic U46619 (15 [(S)-hydroxy11a,9a-(epoxymethano)prosta-5Z,13E-dienoic acid]). Oral LY293111 sodium inhibited leukotriene B4-induced bronchoalveolar lavage granulocyte infiltration and delayed onset airway obstruction at doses as low as 0.3 mg/kg. In A23187-challenged animals, pulmonary inflammation was markedly inhibited at 1 h, but not 2 h and 4 h post-exposure. We conclude that LY293 11 sodium is a selective leukotriene B4 receptor antagonist with potent pulmonary anti-inflammatory activity.

Leukotriene receptor antagonism and augmentation of beta-receptor-mediated events by LY171883.

LY171883, (1-[2-hydroxy-3-propyl-4-[4(1H-tetrazol-5-yl)butoxy)phenyl]etha none), a leukotriene (LT) D4/E4 receptor antagonist, was assessed in comparison with two well known phosphodiesterase inhibitors, isobutylmethyl-xanthine (IBMX) and theophylline, for its ability to augment beta-receptor-mediated responses. Relaxation of carbachol-contracted guinea-pig trachea by isoprenaline was enhanced by the three agents in a dose-dependent manner. A two-fold enhancement of isoprenaline-induced smooth muscle relaxation was produced by 2.5 microM IBMX, 28 microM LY171883, or 140 microM theophylline. Similar concentrations of IBMX or theophylline did not antagonize LTE4-induced tracheal contractions; LY171883 totally inhibited the response and had significant LTE4 receptor antagonist activity even at 10-fold lower concentrations. Antigen-induced release of histamine and LTC4 from guinea-pig lung was reduced by isoprenaline. Prior treatment with LY171883, IBMX, or theophylline did not enhance this action. Isoprenaline reduced histamine-induced bronchospasm in anaesthetized guinea-pigs. LY171883, 30 mg kg-1, or IBMX, 1 mg kg-1, did not affect the isoprenaline-induced decrease in the histamine response. IBMX, 3 mg kg-1, and theophylline, 30 mg kg-1, augmented the isoprenaline-induced bronchodilation. LTE4-induced bronchoconstriction was not affected by IBMX or theophylline whereas LY171883 antagonized this response at doses as low as 3 mg kg-1. Therefore, in both in-vitro and in-vivo test systems, LY171883 functioned primarily as a leukotriene receptor antagonist with minimal pharmacological activity attributable to its ability to potentiate isoprenaline.

Mechanism of fasting-induced suppression of acetaminophen glucuronidation in the rat.

These studies have revealed the occurrence of important relationships among nutritional status, hepatic intermediary metabolism, acetaminophen glucuronidation and susceptibility to hepatotoxicity. During an acute fast hepatic metabolism of glucose is altered profoundly. The altered metabolic poise of the fasted liver appears to favor higher G6P'-ase activity relative to UDPG pyrophosphorylase activity, resulting in decreased production of UDPG secondary to depleted glycogen levels. Although the rate of gluconeogenesis is enhanced and maintains UDPG levels at approximately 60% of those in fed animals, the decreased production of UDPG limits the rate of UDPGA synthesis for glucuronidation of high doses of acetaminophen. Since glucuronidation is the major pathway of clearance of these high doses of the drug, UDPG synthesis is rate-limiting for acetaminophen elimination; the resulting prolongation of the drug half-life is associated with increased amount of reactive metabolite formed and potentiation of liver injury. Glucuronidation is also the major pathway of clearance in the human overdose situation and if UDPG production occupies a similar rate-determining role, then enhancement of UDPG production might be of significant value in the therapy of acetaminophen overdosage. Thus, determination of factors which control UDPG production in the liver under different physiological (nutritional/hormonal) conditions has both fundamental and practical value.

Rapid method for automated on-line extraction and fractionation of plasma leukotrienes and 12-hydroxy-5,8,10,14-eicosatetraenoic acids by reversed-phase high-performance liquid chromatography.

A method is described for automated on-line extraction and fractionation of plasma leukotrienes (LTs) and (5Z,8Z,10E,14Z)-(12S)-hydroxy-5,8,10,14-eicosate traenoic acid [12(S)-HETE] by reversed-phase high-performance liquid chromatography (RP-HPLC). This method was utilized to assess the accuracy of leukotriene B4 (LTB4) and leukotriene C4 (LTC4) determinations obtained by direct immunoassay of guinea pig plasma. Plasma LTB4 levels were significantly higher (p less than 0.01) and plasma LTC4 levels were unchanged when immunoassays were performed post versus pre RP-HPLC fractionation. Rapid separation, high recovery and baseline separation of LTB4, LTC4 and 12(S)-HETE, and minimal hardware requirements clearly demonstrate the general utility of this method.

Vasodilation and aging evaluated in the isolated perfused rat mesenteric vascular bed: preliminary observations on the vascular pharmacology of dobutamine.

The influence of animal age of drug-induced vasodilation was investigated in the perfused rat mesentery constricted with norepinephrine. Responses to isoproterenol, a beta-receptor stimulant, decreased with increasing age. Also, there was a modest decline in the relaxation produced by papaverine. In contrast, dilation of the rat mesentery by acetylcholine, histamine, or nitroglycerin either did not change with age or the responses became somewhat larger. Dobutamine, a myocardial beta-receptor stimulant, produced a marked relaxation of the mesentery. A comparison of the action of isoproterenol and dobutamine revealed that isoproterenol stimulated vascular beta-receptors, whereas dobutamine relaxed the mesentery by antagonizing the tone produced by norepinephrine. The dilation resulting from the alpha-receptor-blocking action of dobutamine was unrelated to animal age.