Slow-reacting substances and their structural elucidation

For more than forty years since their discovery, the structure of a group of closely related materials known collectively as slow-reacting substances has been unknown. These substances are released from a variety of tissues in response to immunological or non-immunological stimulation. A slow-reacting substance is believed to be implicated in hypersensitivity reactions such as asthma; in order to fully understand its bronchoconstrictor role, the structural elucidation of these materials has been a necessary (albeit difficult) task. Studies on both immunologically generated slow-reacting substance of anaphylaxis (SRS-A) and other slow-reacting substances (SRSs) have indicated a precursor role for arachidonic acid in their biosynthesis; this, coupled with enzymic and chemical activity destruction data, gave an insight into the structure of these moieties. In order to define the structure of these materials homogeneous SRS-A was required; a purification scheme was developed relying on the high resolution separative capability of reverse-phase high pressure liquid chromatography, resulting in extensively purified SRS-A. It was then possible to demonstrate that SRS-A possessed a characteristic ultraviolet spectrum, allowing us for the first time to define a major structural moiety in the molecule (conjugated triene). To complement studies on, and to act as a model for the more pathologically relevant SRS-A, a slow-reacting substance was produced from rat basophilic leukaemia (RBL-1) cells. The structure of this biologically active species has been determined by mass spectrometric examination of the intact molecule as a derivative, together with analytical protein chemical studies, and shown to be the novel peptidolipid 5-hydroxy-6-cysteinylglycinyl-7,9,11,14-eicosatetraenoic acid.

Reactive oxygen species mediate endothelium-dependent relaxations in tetrahydrobiopterin-deficient mice

(6R)-5,6,7,8-Tetrahydro-biopterin (H(4)B) is essential for the catalytic activity of all NO synthases. The hyperphenylalaninemic mouse mutant (hph-1) displays 90% deficiency of the GTP cyclohydrolase I, the rate-limiting enzyme in H(4)B synthesis. A relative shortage of H(4)B may shift the balance between endothelial NO synthase (eNOS)-catalyzed generation of NO and reactive oxygen species. Therefore, the hph-1 mouse represents a unique model to assess the effect of chronic H(4)B deficiency on endothelial function. Aortas from 8-week-old hph-1 and wild-type mice (C57BLxCBA) were compared. H(4)B levels were determined by high-performance liquid chromatography and NO synthase activity by [(3)H]citrulline assay in homogenized tissue. Superoxide production by the chemiluminescence method was measured. Isometric tension was continuously recorded. The intracellular levels of H(4)B as well as constitutive NO synthase activity were significantly lower in hph-1 compared with wild-type mice. Systolic blood pressure was increased in hph-1 mice. However, endothelium-dependent relaxations to acetylcholine were present in both groups and abolished by inhibition of NO synthase with N(G)-nitro-L-arginine methyl ester as well. Only in hph-1 mice were the relaxations inhibited by catalase and enhanced by superoxide dismutase. After incubation with exogenous H(4)B, the differences between the 2 groups disappeared. Our findings demonstrate that H(4)B deficiency leads to eNOS dysfunction with the formation of reactive oxygen species, which become mediators of endothelium-dependent relaxations. A decreased availability of H(4)B may favor an impaired activity of eNOS and thus contribute to the development of vascular diseases.

Nippostrongylus brasiliensis: infection induces upregulation of acetylcholinesterase activity on rat intestinal epithelial cells

Expression of cholines terases and muscarinic acetylcholine receptors in the jejunal mucosa has been investigated during infection of rats with the nematode parasite Nippostrongylus brasiliensis. Selective expression of m3 receptors was observed on epithelial cells from uninfected rats and animals 7 days postinfection, and saturation binding with [(3)H]quinuclidinyl benzilate indicated that receptor expression on cell membranes was unaltered by infection. Butyrylcholinesterase was highly expressed in mucosal epithelia, but acetylcholinesterase was present at low levels in uninfected animals. In contrast, discrete foci of intense acetylcholinesterase activity were observed on the basement membrane of intestinal epithelial cells in animals infected with N. brasiliensis. This was demonstrated to be due to upregulation of expression of endogenous enzyme, which peaked at Day 10 postinfection and subsequently declined to preinfection levels. It is suggested that this occurs in response to hyper-activation of the enteric nervous system as a result of infection, and may benefit the host by limiting excessive fluid secretion due to cholinergic stimulation.

Different Effects of Lipopolysaccharide on Plasminogen Activator Inhibitor-1 Production in Aortic Media in Vivo and in Culture

Background: Lipopolysaccharide (endotoxin) has been shown to increase the expression of plasminogen activator inhibitor type-1 (PAI-1) in the vessel wall. Endotoxin is known to increase PAI-1 production in endothelial cells, but its action on smooth muscle cells (SMCs) is presently not clear. In this study we determined the effect of endotoxin on PAI-1 and tissue plasminogen activator (t-PA) production by aortic SMCs in vivo in two animal species, and in culture. Methods: The aortas of Sprague Dawley rats and of New Zealand White rabbits were rapidly excised after parenteral administration of endotoxin. Total RNA was extracted from the aortic media, and PAI-1 and t-PA mRNA levels were quantified after Northern blotting. In addition, cultured rat aortic SMCs were treated with endotoxin. PAI activity in the conditioned medium was determined with a spectrophotometric assay, and total RNA was extracted from the cells and analyzed. Results: A rapid and strong induction in the aortic medi a of PAI-1 mRNA was observed by endotoxin in both rat (50 mg/kg) and rabbit (1 mg/kg). t-PA mRNA was barely detectable and was not increased by endotoxin. Studies in cultured SMCs showed low expression of PAI-1 mRNA under serum-free conditions and little PAI activity in the cell-conditioned medium. Endotoxin did not increase the levels of PAI-1 mRNA nor PAI activity under serum-free conditions. The effect of endotoxin (10 mg/ml) in the presence of 10% (v/v) newborn calf serum on PAI-1 mRNA was negligible; PAI activity, however, increased by 50.3 +/- 7.3% compared with controls. mRNA levels of t-PA and low-density lipoprotein/receptor-related protein/alpha2-macroglobulin receptor also increased after endotoxin administration. PAI activity was identified as PAI-1 by immunoblotting. Fibrin zymography showed that t-PA was present only in complex with PAI-1. Conclusions: A strong increase in PAI-1 gene expression by endotoxin was observed in aortic SMCs in vivo but not in culture. Th is suggests that the effect of endotoxin on SMCs is indirect. The fibrinolytic/proteolytic potential of the SMCs in the vessel wall is likely to have important implications for the migration of cells during vessel wall remodeling, such as neointima formation, during tumor cell metastasis, and for the fate of intramural thrombi.

Regional variations in endothelin-1 and its receptor subtypes in human coronary vasculature: pathophysiological implications in coronary disease

Endothelin-1 is a potent vasoconstrictor peptide and mitogen for vascular smooth muscle cells. Increased plasma or tissue levels of endothelin-1 have been described after myocardial infarction and in atherosclerosis, suggesting that this peptide may play a pathophysiological role in various coronary syndromes. Here, we have studied regional variations in ET-1 and its receptors in control and atherosclerotic human coronary vasculature using standard immunohistochemistry and in vitro autoradiography. ET-1 immunoreactivity was associated with luminal endothelial cells and smooth muscle cells at regions of atherosclerosis. ET(A) receptors were present on smooth muscle cells of coronary arteries and on cardiac myocytes. Medial ET(B) receptor binding at the proximal region of coronary arteries was weak, but increased significantly towards distal regions of this vessel (p<0.005 in control and p<0.0005 in ischaemic heart disease). Microvascular endothelial cells in the adventitia of coronary arteries, myocardial microvessels and the endocardial endothelium expressed the ET(B) receptor exclusively. The receptor variations revealed in this study provide supporting evidence that ET-1 is associated with (1) vascular smooth muscle and endothelial cell proliferation, including areas of intimal hyperplasia and regions of neovascularization (2) increased ET-1-induced reactivity of distal portions of the human coronary artery, (3) ET-1-mediated constriction of myocardial microvessels. These results provide new insights into different potential roles for this peptide in healthy and diseased human coronary vasculature.

Actions of 8 epi prostaglandin F2alpha on isolated rat aorta

8-epi prostaglandin F2alpha(8-epi PGF2alpha) contracted rat thoracic aorta rings in a concentration-dependent manner in the presence or absence of functional endothelium [median effective concentration (EC50) values, 455+/-52 and 268+/-34 nM, respectively; Student's t test; p=0.006]. U46619 was a more potent agonist with or without functional endothelium (EC50 values, 6.8+/-1.6 and 4.5+/-1.0 nM, respectively). SQ29548 [a thromboxane (TP)-receptor antagonist] inhibited contractions to both 8-epi PGF2alpha and U46619 in a competitive manner, with mean pA2 values of 8.3 and 7.9, respectively. 8-Epi PGF2alpha had a further contractile effect in vessels that had been contracted with noradrenaline and had been shown to possess a functional endothelium. Inhibition of thromboxane synthesis with OKY-046 or blockade of endothelin receptors with bosentan had no effect on responses to 8-epi PGF2alpha or U46619. Preincubation with 8-epi PGF2alpha or noradrenaline shifted the concentration-response curves to U46619 upward at low concentrations of U46619 with no significant change in EC50 values or maximal responses. Reduction of TP-receptor number in rat aorta with dithiothreitol caused a concentration-dependent inhibition of responses to both U46619 and 8-epi PGF2alpha, with no effect on maximal responses and or on the responses to U46619 after the preincubation with 8-epi PGF2alpha. These results indicate that 8-epi PGF2alpha is a potent vasoconstrictor in the rat aorta and are suggestive of an action of 8-epi PGF2alpha at the TP receptor.

Hypothalamic hypertensive factor: an inhibitor of nitric oxide synthase activity

Human and rat plasma and rat hypothalamus contain a cytochemically detectable substance, the concentration of which rises with an increase in salt intake. The plasma concentration of this material is also raised in essential hypertension and in the spontaneously hypertensive rat (SHR), the Milan hypertensive rat, and the reduced renal mass (RRM) hypertensive rat. In the normal rat, the greatest concentration is found in the hypothalamus of the SHR and the RRM hypertensive rat. The physicochemical characteristics of this cytochemically detectable hypothalamic hypertensive factor (HHF), including chromatographic behavior and molecular weight range, suggest that it may share features common to a substituted guanidine that is present in established nitric oxide synthase (NOS) inhibitors. It was therefore decided to determine the effect on NOS activity of the HHF obtained from mature SHR. The ability of HHF to inhibit NOS activity was studied on (1) NOS extracted from bovine aorta, rat brain, and human platelets by measuring the conversion of radiolabeled L-arginine to L-citrulline and (2) rat liver NOS measured indirectly with a cytochemical technique based on the stimulation of soluble guanylate cyclase activity in hepatocytes by NO. HHF showed a biphasic inhibitory action on platelet NOS activity that was greater with HHF obtained from SHR than from Wistar-Kyoto rats. HHF also had a biphasic inhibitory effect on hepatocyte NOS activity that was more potent when obtained from SHR. It is proposed that the increase in HHF, a novel form of NOS inhibitor that is elevated in SHR, may be involved in the rise in arterial pressure.

Coronary artery constriction by the isoprostane 8-epi prostaglandin F2 alpha

1. This study was undertaken to compare the effects of 8-epi prostaglandin F2 alpha (8-epi PGF2 alpha) to those of prostaglandin F2 alpha (PGF2 alpha) and U46619, a thromboxane mimetic, on ovine, bovine and porcine coronary arteries. 2. 8-epi PGF2 alpha constricted porcine and bovine coronary arteries in a concentration-dependent manner with EC50 values of 689.0 +/- 229.3 and 1361.0 +/- 272.3 nM, respectively, but had no effect on ovine coronary arteries. 3. U46619 was a potent vasoconstrictor of porcine, ovine and bovine coronary arteries with EC50 values of 33.0 +/- 23.5, 373.3 +/- 69.7 and 254.1 +/- 134.3 nM, respectively. Emax values were significantly greater than those obtained with 8-epi PGF2 alpha. 4. PGF2 alpha constricted procine and bovine coronary arteries in a concentration-dependent manner with EC50 values of 1631.0 +/- 207.6 and 3644.0 +/- 344.8 nM, respectively, but had no effect on ovine coronary arteries. 5. Concentration-dependent constriction to U46619 in porcine coronary arteries was competitively inhibited by SQ29548 (10(-8) M to 10(-7) M) and BM13505 (10(-8) M to 10(-6) M) with no decrease in maximal responses. 6. Concentration-dependent constriction to 8-epi PGF2 alpha in porcine coronary arteries was inhibited in a concentration-dependent manner by SQ29548 (10(-8) M to 10(-7) M) and BM13505 (10(-8) M to 10(-6) M). However, the inhibition was associated with a decrease in maximal response. 7. Maximal responses of porcine coronary artery to U46619 (1 microM) and 8-epi PGF2 alpha (30 microM) were inhibited in a concentration-dependent manner by SQ29548 with IC50 values 99 +/- 12.36 nM and 46.5 +/- 18.67 nM, respectively. 8. Although ovine coronary arteries did not constrict to 8-epi PGF2 alpha pre-incubation of these vessels with 8-epi PGF2 alpha caused a rightward shift of the U46619 response curve in a concentration-dependent manner. 9. Pre-incubation of porcine coronary arteries with 8-epi PGF2 alpha competitively inhibited responses to U46619 with a Schild slope of 0.99 and a pA2 of 6.13. 10. We conclude that 8-epi PGF2 alpha is a vasoconstrictor within porcine and bovine coronary arteries, with a potency approximately twice that of PGF2 alpha but 5-20 times lower than U46619. The data suggest that 8-epi PGF2 alpha is acting as a partial agonist on the TP-receptor in the coronary vasculature.

WEB 2086 inhibits neutrophil dependent increases in coronary resistance in blood perfused rabbit heart

OBJECTIVE

The aim was to investigate the mechanism of the pressor action of the chemotactic peptide formyl-methionyl-leucyl-phenylalanine in the blood perfused Langendorff preparation of the isolated rabbit heart; and in particular to establish whether the response was dependent on the presence of neutrophils and whether the release of platelet activating factor contributed to the pressor effect.

METHODS

An isolated rabbit heart was perfused with blood from an anesthetised support rabbit. Formyl-methionyl-leucyl-phenylalanine was injected intra-arterially proximal to the isolated heart and measures of cardiac performance recorded. In some experiments the support animal was depleted of neutrophils by pretreatment with mechlorethamine while in others the specific platelet activating factor receptor antagonist WEB 2086 was given to the support animal before formyl-methionyl-leucyl-phenylalanine. Differential blood cell counts were determined throughout the course of each experiment. Each heart was examined histologically after the experiment.

RESULTS

Formyl-methionyl-leucyl-phenylalanine caused a significant rise in perfusion pressure which was virtually abolished by leucocyte depletion of the support animal. The response could also be reduced by about 80% with intravenous WEB 2086. Histological examination of the perfused hearts showed that the number of accumulated neutrophils was very variable and not correlated with the rise in perfusion pressure. There was no significant difference between control hearts and those receiving WEB 2086.

CONCLUSIONS

The results confirm previous reports that the response to formyl-methionyl-leucyl-phenylalanine is neutrophil dependent and show that this model of a blood perfused heart can be used successfully to examine the response to a leucocyte dependent stimulus. The results also suggest that the response to formyl-methionyl-leucyl-phenylalanine may not only be due to physical obstruction of the coronary circulation or "neutrophil plugging", but may also be due to the release of platelet activating factor.

Interactions between second messengers: cyclic AMP and phospholipase A2- and phospholipase C-metabolites

The article reviews several new findings on the interactions between phospholipase A2- and phospholipase C-derived metabolites and cyclic AMP, in view of the developments recently achieved in studies on intracellular signal transduction. A complex network of multi-directional regulative mechanisms in the airways and inflammatory blood cells is briefly outlined.

Structure-activity relationship of human calcitonin-gene-related peptide

The calcitonin-calcitonin-gene-related peptide (CGRP) gene complex encodes a small family of peptides: calcitonin, CGRP and katacalcin. Calcitonin is a circulating hormone that prevents skeletal breakdown by inhibiting the resorption of bone by osteoclasts. CGRP, a potent vasodilator, is involved in normal regulation of blood flow. The calcitonins structurally resemble the CGRP peptides, and both are known to cross-react at each others' receptors. The present study was undertaken to examine the structural prerequisites for biological activity of the intact CGRP molecule. We therefore prepared eight chymotryptic and tryptic fragments of CGRP and synthesized its acetylated and S-carboxyamidomethylcysteinyl analogues. The analogues were purified by h.p.l.c. and their structures were confirmed by fast-atom bombardment mass spectrometry. We have examined the effects of structurally modified analogues and fragments of human CGRP in a calcitonin-receptor-mediated assay, the osteoclast bone resorption assay, and in one or two CGRP-receptor-mediated assays, the rabbit skin blood flow assay and the oedema formation assay. The results showed that (1) in the osteoclast bone resorption assay, both CGRP peptides, alpha and beta, were equipotent, and were both at least 1000-fold were both approx. 1000-fold more potent than salmon calcitonin; human calcitonin had no effect; (3) the bis- and N-acetylated CGRP analogues retained reduced levels of biological activity in all assays, whereas S-carboxyamidomethylcysteinyl-human CGRP was without activity; and (4) all tryptic and chymotryptic fragments of CGRP were without biological activity, with the exception of hCGRP-(Ala1-Lys35): this fragment had much reduced activity compared with the intact peptide in inhibiting osteoclastic bone resorption and increasing blood flow in the rabbit skin. The results suggest that: (1) calcitonin and CGRP act at distinct receptors to mediate different physiological effects; (2) minor amino acid substitutions, as between the alpha and beta forms of CGRP (these two forms have 94% structural similarity) do not result in differences in biological activity; (3) the intact peptide is required for full biological activity of the CGRP molecule, and even the loss of two amino acids at the C-terminus of the molecule results in a marked decrease in activity; (4) the disulphide bridge appears to play an important role in the interaction of the intact CGRP molecule with its receptor; and (5) the C-terminal region is probably necessary for the peptide to assume the right conformation in the interaction with the receptor.

The synthesis, release and action of leukotrienes in the isolated, unstimulated, buffer-perfused rat heart

When the perfusion medium of an isolated, non-recirculating, Langendorff rat heart is changed from Krebs buffer to coronary effluent, a significant vasoconstriction (23%, P less than 0.005) is observed. In this study we have investigated the involvement of leukotrienes in this phenomenon. We have extracted and quantified leukotrienes C4, D4 and E4 in samples of coronary effluent taken at different times during the first 2 h of perfusion; the total amounts released during this time were 9, 5 and 32 pmol of LTC4, LTD4 and LTE4 respectively. We have used two different methods to prevent the action of the effluent leukotrienes on the heart. Firstly, we have blocked the leukotriene receptors in the heart, with FPL 55712 (3.8 microM), during perfusion with effluent and, secondly, we have perfused with coronary effluent which was collected in the presence of a leukotriene synthesis inhibitor, AA861 (1 microM). The addition of FPL 55712 to the effluent decreased the normally observed vasoconstriction such that after 30 min the coronary flow rate (CFR) was 114 +/- 3% (n = 6) compared with 66 +/- 1% (n = 7) with effluent alone (P less than 0.005). Effluent collected in the presence of AA861 also caused a decrease in the normally observed vasoconstriction such that by 30 min the CFR was still 88 +/- 2% (n = 6, P less than 0.005 compared to controls). We have confirmed the proposed involvement of leukotrienes in the effluent-induced vasoconstriction by investigating the effect of a mixture of the synthetic leukotrienes C4, D4 and E4, when each of them was present at the same concentration as measured in the coronary effluent; the vasoconstriction observed was superimposable upon that seen with effluent. This vasoactive effect of the leukotriene mixture was not secondary to a change in contractility, since this only decreased to 97 +/- 5% (n = 9) during the 30 min of the leukotriene infusion. Finally, we have studied the effects of the same two leukotriene blockers in normal, buffer-perfused hearts after an initial perfusion of either 30 or 120 min. Application of either AA861 or FPL 55712 resulted in a dramatic vasodilatation (25 to 45% increase), a larger effect always being observed after the shorter initial period of perfusion. Our conclusions are two-fold. Firstly, isolated, buffer-perfused rat hearts synthesize leukotrienes C4, D4 and E4 in considerable amounts and release them into the coronary effluent and secondly, the coronary flow rates of isolated, buffer-perfused rat hearts are partly controlled by the action of internally produced leukotrienes.

The role of cyclic AMP in the inhibition of leukotriene biosynthesis by neuropeptides

Certain neuropeptides, including vasoactive intestinal peptide, inhibit peptidoleukotriene release from platelet activating factor-stimulated rat lung. We have now shown that vasoactive intestinal peptide will also inhibit peptidoleukotriene release from platelet activating factor-stimulated or ovalbumin-challenged guinea pig lung, but not from calcium ionophore-stimulated rat or guinea pig lung. In rat lung a pre-incubation with the peptide prior to addition of platelet activating factor was required for the effect to be maximal. When vasoactive intestinal peptide was substituted with cyclic AMP, the inhibitory effect was reproduced. In addition, pre-incubation with MDL 12330A, an inhibitor of adenylate cyclase, reduced the inhibitory effect of vasoactive intestinal peptide on platelet activating factor-stimulated leukotriene C4 biosynthesis. We suggest that the inhibition of platelet activating factor-stimulated peptidoleukotriene release in rat lung by vasoactive intestinal peptide involves the events prior to phospholipase A2 activation and requires cyclic AMP as a mediator.

Coronary vasodilatation induced by calcitonin gene-related peptide in the anaesthetised pig

The ability of CGRP to increase blood flow in the coronary circulation of the anaesthetized pig was studied in a constant pressure perfusion model. Human alpha-CGRP, when infused close-arterially into the left anterior descending coronary artery perfused at constant pressure, produced a marked and prolonged dose-related increase in coronary flow, at doses above 10 pmol min-1. The gradient of the flow/pressure curves at each dose increased with an increase in pressure, indicating a drop in the resistance of the coronary bed. No significant change was observed in heart rate, left ventricle pressure, mean arterial pressure or cardiac output.

Endothelin-1 is a potent constrictor in conductive and resistive coronary arteries

The action of endothelin-1 (ET-1) in canine and porcine coronary artery ring preparations and perfused canine and porcine myocardium was examined in vitro to determine the site of action of ET-1 in the coronary vasculature. ET-1 had a vasoconstrictor effect that was more potent in smaller diameter ring preparations. The EC50s for both canine and porcine ring preparations decreased with a decrease in vessel diameter and the EC50 of ET-1 in the perfused myocardium was three to four times lower than in the smallest ring preparation. The results suggest that ET-1 may cause cardiac ischemia by constriction of resistive vessels rather than by epicardial coronary artery spasm.

Endothelin induces potent microvascular constriction

Endothelin is a recently discovered peptide produced by endothelial cells. It has been shown to have potent constrictor effects on major arteries in vitro and to raise rat blood pressure in vivo. The present experiments show that endothelin has a potent constrictor action on the microvasculature. Blood flow changes were measured by a xenon clearance technique in rabbit skin. Endothelin, when injected intradermally into rabbit skin, decreased local blood flow in a dose-dependent manner. Endothelin reduced basal skin blood flow and reversed the increased blood flow induced by a vasodilator. These results show that endothelin, administered extravascularly, has potent vasoconstrictor activity. This adds further support to the suggestion that endothelin may have an important role in the physiological control of blood flow and pressure.

Leukotriene release by human fetal membranes, placenta and decidua in relation to parturition

Complete placentas and membranes were obtained from women after uncomplicated singleton pregnancies. Six were collected after labour at term, six after preterm labour and six after elective Caesarean section at term. Leukotriene C4 (LTC4), leukotriene D4 (LTD4) and leukotriene E4 (LTE4) release was examined using a short-term incubation technique. Release by amnion was significantly higher than that by the other tissues for the three modes of delivery. Comparison of LTC4, LTD4 and LTE4 release by individual tissues with regard to the type of delivery showed no significant difference.

Bradykinin- and chemotactic peptide fMLP-stimulated leukotriene biosynthesis in rat lungs and its inhibition by vasoactive intestinal peptide

The release/biosynthesis of peptidoleukotrienes (pLT) from rat lung tissue was stimulated with either bradykinin (Bk) or the chemotactic peptide formyl-methionyl-leucinyl-phenylalanine (fMLP). Bk- and fMLP-induced stimulation of pLT levels was dose-related for leukotriene D4 (LTD4), E4 (LTE4) and total pLTs and was maximal when a 10 microM concentration of either peptide was used. This stimulation was partially counteracted by vasoactive intestinal peptide (VIP), in agreement with the previously reported VIP inhibition of platelet activating factor- and IgG-stimulated pLT biosynthesis.

Neuropeptides and leukotriene biosynthesis: the effect of calcitonin, peptide histidine valine-42, helodermin, neuropeptide Y and galanin

The effect of five neuropeptides was tested on platelet activating factor (PAF)-stimulated peptidoleukotriene biosynthesis in rat lungs. Calcitonin and peptide histidine valine-42 (PHV-42) were found to inhibit leukotriene C4 (LTC4) and D4 (LTD4) biosynthesis to an extent similar to the previously reported effects of calcitonin gene-related peptide (CGRP) and peptide histidine isoleucine (PHI) respectively. Helodermin potently inhibited the biosynthesis of all three peptidoleukotrienes. Neuropeptide Y and galanin, both present in airways, enhanced the levels of LTD4 and had no effect on LTC4 or leukotriene E4 (LTE4) levels. The theoretical implications of these findings are discussed.

Platelet activating factor-mediated leukotriene biosynthesis in rat lungs: effect of prostaglandins E1 and F1 alpha

The effect of prostaglandins E1 and F1 alpha on peptidoleukotriene biosynthesis/release from rat chopped lung stimulated with platelet activating factor was studied. Prostaglandin E1, known to stimulate adenylate cyclase in airways, inhibited the biosynthesis of leukotrienes C4, D4 and E4 and total peptidoleukotrienes whereas prostaglandin F1 alpha, which has no effect on adenylate cyclase, did not exert any effect on total peptidoleukotriene release, though a small inhibition was found for leukotriene D4. Cyclic AMP itself inhibited peptidoleukotriene release from platelet activating factor-stimulated lung, suggesting that the effect of prostaglandin E1 is mediated by cyclic AMP.

Leukotriene release by endometrium and myometrium throughout the menstrual cycle in dysmenorrhoea and menorrhagia

Endometrium and myometrium were collected at hysterectomy from 21 women with measured menstrual blood loss. Eight women complained of dysmenorrhea and the remaining 13 had pain-free periods. Specimens were obtained throughout the menstrual cycle (menstrual, n = 5; follicular, n = 4; early luteal, n = 3; mid-luteal, n = 5; late luteal, n = 4). Leukotriene C4, leukotriene D4 and leukotriene E4 release were examined using a short-term incubation technique. Endometrial leukotriene release, which was always significantly greater than myometrial release, changed throughout the menstrual cycle and the highest concentrations were found during menstruation. Endometrial, but not myometrial, leukotriene concentrations were significantly higher in tissues obtained from women with a complaint of dysmenorrhoea compared with those in tissue from pain-free women. No correlation was found between leukotriene release in either endometrium or myometrium and menstrual blood loss (range 15-457 ml).

Neuropeptides and leukotriene release: effect of peptide histidine isoleucine and secretin in platelet activating factor-stimulated rat lung

We have previously demonstrated that vasoactive intestinal peptide and calcitonin gene-related peptide inhibit leukotriene release from platelet activating factor-stimulated rat lung. We now report evidence that Peptide Histidine Isoleucine and Secretin, two naturally occurring peptides which are structurally homologous to vasoactive intestinal peptide, show a significant ability to inhibit leukotriene release in the same animal model. A preliminary hypothesis about the mechanism of this inhibition by the neuropeptides is discussed.

The effect of vasoactive intestinal peptide and calcitonin gene-related peptide on peptidoleukotriene release from platelet activating factor stimulated rat lungs and ionophore stimulated guinea pig lungs

The effect of four neuropeptides and acetylcholine on the release of leukotrienes LTC4, LTD4 and LTE4 from platelet activating factor-stimulated rat lung and ionophore A23187-stimulated guinea pig lung, as detected by the combined use of HPLC and radioimmunoassay, was studied. Both vasoactive intestinal peptide and calcitonin gene-related peptide were found to inhibit the release of leukotrienes in both preparations. This effect was most marked in platelet activating factor-stimulated rat lung, where inhibition of LTC4 release was more pronounced than either inhibition of LTD4 or LTE4 production. The effect of vasoactive intestinal peptide on LTC4 biosynthesis was dose-related in rat lung. Neither substance P nor beta-endorphin were found to inhibit leukotriene release in rat lung. Vasoactive intestinal peptide inhibition of leukotriene release is independent from its actions on the muscarinic receptor, since acetylcholine was found to have no effect in the same preparation.

CGRP: a novel neuropeptide from the calcitonin gene is the most potent vasodilator known

The calcitonin gene has been shown to give rise to another peptide, calcitonin gene-related peptide (CGRP). The structure of human CGRP has been determined by mass spectrometry. Calcitonin gene-related peptide-containing neurons have been detected in a number of species, particularly in association with heart and blood vessels. Pharmacological studies have shown that CGRP is a potent vasodilator in a number of vessels and vascular beds, including the skin and coronary circulation. Investigations in humans have also reported the potent vasodilator action of CGRP. The evidence from these studies suggests that CGRP is an important regulator of vascular tone and blood flow.

Potent vasodilator activity of calcitonin gene-related peptide in human skin

We have recently shown that the novel neuropeptide calcitonin gene-related peptide, CGRP, is a potent vasodilator. In this paper we report a detailed study of the effects of CGRP in human skin. CGRP induces a clearly defined, long-lasting erythema. We have measured the effect of CGRP on blood flow in human skin using a laser Doppler technique and have demonstrated increased local blood flow that persists for a number of hours. We compared the response of CGRP with other known vasodilators [histamine, prostaglandin (PG) E2, PGI2, substance P, and vasoactive intestinal peptide (VIP)] in the skin, and in all subjects the erythema induced by CGRP was more persistent than that induced by the other mediators tested. Except at high doses the local vasodilatation induced by CGRP was not associated with a wheal and flare as seen with histamine, substance P, and VIP. CGRP is an extremely potent vasodilator and if released into the circulation, or locally from peripheral nerve endings, it could have a role in the regulation of blood flow in both physiologic and pathologic conditions; CGRP may be the endogenous mediator of the flare in the triple response. A deficiency in CGRP secretion or action could be an important component of peripheral vascular disease. Some flushing reactions (e.g., those associated with medullary thyroid carcinoma) may result from circulating CGRP.

Investigation of the structure/activity relationship of human calcitonin gene-related peptide (CGRP)

The biological activities of calcitonin gene-related peptide (CGRP) enzymic digest fragments, chemically modified products and beta-CGRP have been compared to that of intact alpha-CGRP on rat isolated paired atria. Tryptic and chymotryptic digests both produced inactive fragments. Acetylation of the N-terminal amino acid (Alanine) or either of Lys 24 or Lys 35, resulted in reduced, but measurable, biological activity. Destruction of the disulphide bridge between Cys 2 and Cys 7 abolished biological activity. Substitution of several amino acids, Asp 3, Val 22 and Asn 25, with Asn, Met and Ser respectively (beta-CGRP), produced a peptide with similar biological activity to alpha-CGRP.

Calcitonin gene-related peptide is a potent vasodilator

A novel peptide, calcitonin gene-related peptide (CGRP), has been predicted to result from alternative processing of the primary RNA transcript of the calcitonin gene in the rat. Several lines of evidence suggest that CGRP is a transmitter in the central and peripheral nervous system. Human CGRP has been isolated and characterized, and shown to have potent effects on the heart. The observations presented here indicate that human and rat CGRP also have potent effects on blood vessels. Intradermal injection of CGRP in femtomole doses induces microvascular dilatation resulting in increased blood flow, which we have detected in the rabbit by using a 133Xe clearance technique. In human skin, CGRP induces persistent local reddening. Microscopic observation of the hamster cheek pouch in vivo revealed that topical application of CGRP induces dilatation of arterioles. Furthermore, CGRP relaxes strips of rat aorta in vitro by an endothelial cell-dependent mechanism. Therefore, we suggest that local extravascular release of CGRP may be involved in the physiological control of blood flow and that circulating CGRP may contribute to hyperaemia in certain pathological conditions.

Leukotriene biosynthesis and metabolism detected by the combined use of HPLC and radioimmunoassay

A radioimmunoassay for leukotriene D4 (LTD4) has been developed which exhibits sufficiently high sensitivity to be useful in conjunction with RP-HPLC in the detection of LTC4, LTD4 and LTE4 in physiological samples. The detection limit of the assay was approximately 240 amoles, using antiserum TG1 at a dilution of 6 X 10(3), with 50% displacement at 70 fmoles. Antiserum NW1, also at a dilution of 6 X 10(3), displayed a detection limit of 9 fmoles with 50% displacement at 100 fmoles. The two antisera have similiar crossreactivities, both manifesting useful affinities for LTE4 and LTC4, and low or negligible affinities for other arachidonic acid metabolites, or their derivatives. The radioimmunoassay was used to detect 1) LTC4, LTD4 and LTE4 released from perfused rat lung in response to platelet-activating factor (PAF) stimulation, 2) conversion of exogenous LTD4 to LTE4 in human blood, and 3) endogenous leukotrienes in human blood samples.

Platelet-activating factor stimulation of peptidoleukotriene release: inhibition by vasoactive polypeptide

Leukotriene (LT) release stimulated by platelet activating factor was inhibited by vasoactive intestinal polypeptide (VIP) in an in vitro rat lung preparation. This was detected by HPLC and radioimmunoassay. LTC4, although the major species in the stimulatory model used, was not detected in peptide-treated preparations and LTD4 and LTE4 levels were considerably reduced.

The myotropic and plasma-calcium modulating effects of calcitonin gene-related peptide (CGRP)

Human and rat calcitonin gene-related peptides cause a dose-related contraction of guinea pig ileum, which is antagonised by an anti-histamine, mepyramine, and an anticholinergic compound, hyoscine. Both peptides also cause a positive inotropic and a positive chronotropic effect in the rat isolated auricle and these responses are antagonised by propranolol, a B adrenoceptor blocker. Further, the peptides lower plasma calcium levels in both rats and rabbits in a dose-related manner resembling calcitonin; in the rabbit, but not in the rat, the initial calcium lowering effect is succeeded by hypercalcaemia at higher doses, while in the chick, only the parathyroid hormone-like calcium-raising effect is seen.

Slow reacting substances (leukotrienes): enzymes involved in their biosynthesis

Slow reacting substances (leukotrienes C4, D4, E4) are synthesized in vivo by a combination of two previously unrelated pathways: lipoxygenase oxygenation of arachidonic acid and the glutathione detoxification pathway. Enzymes involved in the latter pathway (glutathione transferase [RX: glutathione R-transferase, EC 2.5.1.18]; gamma-glutamyltransferase [(5-glutamyl)-peptide: amino acid 5-glutamyltransferase, EC 2.3.2.2] ) have been investigated in guinea pig lung and rat basophilic leukemia (RBL-1) cells. We report data on levels of enzymic activity both before and during the release of slow reacting substances. Both glutathione transferase and gamma-glutamyltransferase are present in significant quantities in guinea pig lung and RBL-1 cells. A model for the changes in gamma-glutamyltransferase during leukotriene release is proposed for the cell line, and differences from the guinea pig lung system are reported. Leukotriene C4 is converted to the more potent leukotriene D4 by the action of gamma-glutamyltransferase on guinea pig ileum during bioassay. gamma-Glutamyltransferase may represent a control feature in the biosynthesis of leukotriene D4, and thus be involved in leukotriene-induced bronchoconstriction in the lung.

Preparation, purification, and structure elucidation of slow-reacting substance of anaphylaxis from guinea pig lung

The work that we have described had originally three main aims: (a) to design a new purification system for SRS-A from which we would obtain pure material for the structural analysis: (b) to define the functional groups in the pure material by spectrophotometric, chemical, and enzymic inactivation methods; and (c) to deduce the complete covalent structure by an accepted spectroscopic method capable of defining structure in atomic detail. These aims have been achieved. The structure of SRS-A, the physiologically more relevant example of the SRSs that were studied, because it was derived immunologically from an animal model of an acute hypersensitivity reaction, has been rigorously defined. Of paramount importance in the determination of this structure was the mass spectrometric analysis of the intact molecule. Degradative and comparative studies are not capable of unequivocally defining structure. For example, the mass spectrum clearly showed the absence of an amide or similar C-terminal blocking groups or, as has been suggested, a sulfone in the molecule; such conclusions could not be drawn from comparative chromatographic data even on multiple systems. Mass spectrometric analysis of the intact molecule could overcome these problems by allowing the complete covalent structure to be collated from the information obtained from each fragmentation. The use of stable isotopes and accurate mass measurement removed possible ambiguities in the interpretation, and the sensitivity and specificity of mass spectrometry made it the method of choice for the structural analysis.

Slow-reacting substances and their formation by a lipoxygenase pathway

Slow-reacting substances are formed from arachidonic acid by the action of a lipoxygenase, which leads to the formation of 5-hydroperoxy, 6, 8, 11, 14 eicosatetraenoic acid. The covalent structures of SRS-A from guinea-pig lung and SRS from RBL-1 cells have been determined by protein chemical analysis and electron impact mass spectrometry of a derivative of the intact molecules. The structures of SRS-A and SRS are identical, being 5-hydroxy-6-cysteinyl-glycinyl-7, 9, 11, 14-eicosatetraenoic acid. SRSs may be formed by a combination of the metabolism of arachidonic acid by the lipoxygenase pathway and the glutathione detoxification pathway involving nucleophilic attack on 5,6-oxidoeicosatetraenoic acid.

Slow reacting substance of anaphylaxis, SRS-A; assignment of the stereochemistry

We have recently described the structure elucidation of slow reacting substance of anaphylaxis S(SRS-A) from lung and of a slow reacting substance (SRS) from basophilic leukaemia cells as 5-hydroxy-6-cysteinylglycinyl-7,9,11,14-eicosatetraenoic acid. The stereochemistry of this molecule has now been shown to be 5(S)-hydroxy- 6(R)-cysteinylghlycinyl-7,9-trans-11,14-ciseicosatetraenoic acid by comparison of the synthetic and natural products and their derivatives using mass spectrometric and HPLC chromatographic techniques. The synthetic and natural compounds are also indistinguishable by their pharmacological properties, their conversion by soybean lipoxygenase, and their UV spectra.

The role of arachidonate lipoxygenase in the release of SRS-A from guinea-pig chopped lung

The immunological release of SRS-A was investigated in guinea-pig chopped lung. A number of unsaturated fatty acids, all of which are substrates for arachidonate lipoxygenase were found to potentiate the release of SRS-A. This potentiation was enhanced by indomethacin, a cyclo-oxygenase inhibitor, and completely reversed by nordihydroguaiaretic acid (NDGA) and eicosatetraynoic acid (ETA) which inhibit lipoxygenase. This suggests that some aspect of arachidonate lipoxygenase action stimulates release of SRS-A and that release of SRS-A is increased by redirection of arachidonic acid (AA) metabolism via the lipoxygenase pathway (Hamberg, 1976). However, although exogenous 14C-AA increased SRS-A output it was not incorporated into SRS-A.

Slow reacting substances (SRSs): the structure identification of SRSs from rat basophil leukaemia (RBL-1) cells

Slow Reacting Substances have been produced from RBL-l cells by calcium ionophore A23187 and purified to homogeneity by high pressure liquid chromatography (HPLC). The structure of the major biologically active species has been determined by mass spectrometric examination of the intact molecule as a derivative, together with amino-acid analysis and sequence determination. The characteristic triene chromophore which we originally identified in immunologically generated SRS-A is present in RBL-l SRS, and we determine the structure of this SRS as the thio-substituted dipeptide, 5-hydroxy-6-cysteinylglycinyl-7,9,11,14-eicosatetraenoic acid.

Comparative studies on immunologically and non-immunologically produced slow-reacting substances from man, guinea-pig and rat

1 Slow-reacting substance of anaphylaxis (SRS-A) was produced by antigen challenge of passively sensitized human lung and actively sensitized guinea-pig lung. 2 A slow-reacting substance (SRS) was prepared from the peritoneal fluid of rats treated with calcium ionophore A23187. 3 These substances were extensively purified by charcoal adsorption, Sephadex G-15 gel filtration, ether extraction and reverse phase high pressure liquid chromatography. 4 The three substances are pharmacologically, chemically and chromatographically indistinguishable. 5 Our data suggest that the same SRS entities are released from a variety of tissues and that these acidic lipids may have a wider physiological significance than just anaphylaxis.