The effect of Δ9-tetrahydrocannabinol on 5-HT3 receptors depends on the current density.

The effects of Δ(9)-tetrahydrocannabinol (THC), the psychoactive component of cannabis, on the function of 5-HT type 3 (5-HT(3)) receptors were investigated using a two-electrode voltage clamp technique in Xenopus oocytes, and a whole-cell patch clamp technique in rat nodose ganglion neurons. In oocytes injected with 3 ng cRNA of 5-HT(3A) receptor, THC reversibly inhibited currents evoked with 5-HT (1 µM) in a concentration-dependent manner (IC(50)=1.2 µM). The extent of THC inhibition was inversely correlated with the amount of cRNA injected and the mean 5-HT(3A) receptor current densities. Pretreatment with actinomycin D, which inhibits transcription, decreased the mean 5-HT(3) receptor current density and increased the extent of THC inhibition on 5-HT(3) receptor-mediated currents. The IC(50) values for THC increased from 285 nM to 1.2 µM in oocytes injected with 1 and 3 ng of 5-HT(3A) cRNA, respectively. In radioligand binding studies on membrane preparations of oocytes expressing 5-HT(3A) receptors, THC did not alter the specific binding of a 5-HT(3A) receptor antagonist, [(3)H]GR65630. In the presence of 1 µM THC, the maximum 5-HT-induced response was also inhibited without a significant change in 5-HT potency, indicating that THC acts as a noncompetitive antagonist on 5-HT(3) receptors. In adult rat nodose ganglion neurons, application of 1 µM THC caused a significant inhibition of 5-HT(3) receptors, extent of which correlated with the density of 5-HT-induced currents, indicating that the observed THC effects occur in mammalian neurons. The inhibition of 5-HT(3) receptors by THC may contribute to its pharmacological actions in nociception and emesis.

Contact dermatitis in UAE.

Twenty five cases (22 females) who attended the Dermatology out-patient in Dubai dermatology clinic, U.A.E were entered in this study. All of them complained of hand eczema which was diagnosed as contact dermatitis (C D) of the hands. The closed patch test technique was performed for all of them using the standard European battery containing 22 allergens. The results were interpreted and analyzed using the ICDG mode of interpretation after 48 and 96 hours, respectively. We found that nickel sensitivity represented the most common type of sensitivity in hand eczema in both citizens and expatriates living in Dubai, while parabens of perfumes represented the second common sensitizers. We think that patch testing in case of C D of hand is a very good tool for investigating hand eczema.

Streptozotocin-induced diabetic nephropathy in rats: the role of inflammatory cytokines.

The role of inflammatory cytokines in the pathogenesis of diabetic nephropathy has been studied in streptozotocin-induced diabetic rats. Rat kidneys were examined by light and electron microscopy and kidney homogenates were also analyzed by Western blot and flow cytometry for the expression of markers of inflammation namely, CD4+ and CD8+ T cells, macrophages, MHC classes I and II, the proinflammatory cytokines tumor necrosis factor-alpha, interferon-gamma and nitric oxide (NO). Light and electron microscope examination revealed infiltration of mononuclear cells throughout the renal parenchyma, with the glomeruli being more severely affected especially at 8 months after disease induction. Western blot and flow cytometric analyses revealed the infiltrating cells to be CD4+ T cells, CD8+ T cells and macrophages. Western blot analyses also revealed increased expression of the proinflammatory and Th1 cytokines tumor necrosis factor-alpha, interferon-gamma as well as nitric oxide. Using flow cytometry, we have shown that the difference in expression of CD4+ T cells in control and diabetic kidneys is more significant at 1 month than at 8 months, while expression of CD8+ T cells is more significant at 8 months. We speculate therefore that diabetic nephropathy is probably initiated and driven by a Th1 process. CD8+ T cells, however, become more significant at later stages of the disease when tissue loss is evident. Since NO induction also occurs only after 8 months, we hypothesize that NO might be significant for the later stages of the disease. Our data implicate inflammation in the pathogenesis of diabetic nephropathy in view of the overexpression of the proinflammatory cytokines TNF-alpha and IFN-gamma and the cells that secrete them in the early and late phases of the disease.

The Src-protein tyrosine kinase Lck is required for IL-1-mediated costimulatory signaling in Th2 cells.

Src-protein tyrosine kinases are intimately involved in TCR-initiated signaling in T lymphocytes. One member of this family, Lck, is also involved in CD28-mediated costimulation in Th1 cells. In Th2 lymphocytes, the costimulatory signal can also be provided by the interaction of IL-1 with type I IL-1R (IL-1RI), culminating in the activation of NF-kappaB transcription factors. Proximal steps in the IL-1R pathway, however, remain poorly understood, and there is conflicting evidence as to the importance of tyrosine phosphorylation in IL-1R signaling. We have addressed this issue by examining the ability of IL-1 to costimulate the activation of Lck-deficient Th2 cells. Our data demonstrate that, in the absence of Lck, the IL-1 costimulatory pathway is blocked despite the expression of normal levels of IL-1RI. Moreover, the block is associated with a defective degradation of IkappaB-alpha and an incomplete activation of NF-kappaB heterodimeric complexes. Protein expression of NF-kappaB monomers, including p50, p65, and c-Rel, is equivalent in both wild-type and Lck-deficient Th2 cell clones. Finally, we demonstrate that, in normal Th2 cells, stimulation with IL-1 leads to a rapid induction in tyrosine phosphorylation of several substrates including Lck itself. These findings strongly suggest that Lck is required for signaling in the IL-1 costimulatory pathway in Th2 lymphocytes.

FAS activation induces dephosphorylation of SR proteins; dependence on the de novo generation of ceramide and activation of protein phosphatase 1.

The search for potential targets for ceramide action led to the identification of ceramide-activated protein phosphatases (CAPP). To date, two serine/threonine protein phosphatases, protein phosphatase 2A (PP2A) and protein phosphatase 1 (PP1), have been demonstrated to function as ceramide-activated protein phosphatases. In this study, we show that treatment with either anti-FAS IgM (CH-11) (150 ng/ml) or exogenous d-(e)-C(6-)ceramide (20 microm) induces the dephosphorylation of the PP1 substrates, serine/arginine-rich (SR) proteins, in Jurkat acute leukemia T-cells. The serine/threonine protein phosphatase inhibitor, calyculin A, but not the PP2A-specific inhibitor, okadaic acid, inhibited both FAS- and ceramide-induced dephosphorylation of SR proteins. Anti-FAS IgM treatment of Jurkat cells led to a significant increase in levels of endogenous ceramide beginning at 2 h with a maximal increase of 10-fold after 7 h. A 2-h pretreatment of Jurkat cells with fumonisin B(1) (100 microm), a specific inhibitor of CoA-dependent ceramide synthase, blocked 80% of the ceramide generated and completely inhibited the dephosphorylation of SR proteins in response to anti-FAS IgM. Moreover, pretreatment of Jurkat cells with myriocin, a specific inhibitor of serine-palmitoyl transferase (the first step in de novo synthesis of ceramide), also blocked FAS-induced SR protein dephosphorylation, thus demonstrating a role for de novo ceramide. These results were further supported using A549 lung adenocarcinoma cells treated with d-(e)-C(6-)ceramide. Dephosphorylation of SR proteins was inhibited by fumonisin B(1) and by overexpression of glucosylceramide synthase; again implicating endogenous ceramide generated de novo in regulating the dephosphorylation of SR proteins in response to FAS activation. These results establish a specific intracellular pathway involving both de novo ceramide generation and activation of PP1 to mediate the effects of FAS activation on SR proteins.

Cloning and characterization of a novel human alkaline ceramidase. A mammalian enzyme that hydrolyzes phytoceramide.

Ceramidases are enzymes involved in regulating cellular levels of ceramides, sphingoid bases, and their phosphates. Based on sequence homology to the yeast alkaline ceramidases YPC1p (Mao, C., Xu, R., Bielawska, A., and Obeid, L. M. (2000) J. Biol. Chem. 275, 6876--6884) and YDC1p (Mao, C., Xu, R., Bielawska, A., Szulc, Z. M., and Obeid, L. M. (2000) J. Biol Chem. 275, 31369--31378), we report the identification and cloning of a cDNA encoding for a novel human alkaline ceramidase (aPHC) that hydrolyzes phytoceramide selectively. Northern blot analysis showed that aPHC was ubiquitously expressed, with the highest expression in placenta. Green fluorescent protein tagging showed that it was localized in both the Golgi apparatus and endoplasmic reticulum. Overexpression of aPHC in mammalian cells elevated in vitro ceramidase activity toward N-4-nitrobenz-2-oxa-1,3-diazole-C(12)-phytoceramide. Its expression in a yeast mutant strain devoid of any ceramidase activity restored the ceramidase activity and caused an increase in the hydrolysis of phytoceramide in yeast cells, thus leading to the decreased biosynthesis of sphingolipids. These data collectively suggest that, similar to the yeast phytoceramidase YPC1p, aPHC has phytoceramidase activity both in vitro and in cells; hence, it is a functional homolog of the yeast phytoceramidase YPC1p. However, in contrast to YPC1p, aPHC exhibited no reverse activity of ceramidase either in vitro or in cells. Biochemical characterization showed that aPHC had a pH optimum of 9.5, was activated by Ca(2+), but was inhibited by Zn(2+) and sphingosine. Substrate specificity showed that aPHC hydrolyzed phytoceramide preferentially. Together, these data demonstrate that aPHC is a novel human alkaline phytoceramidase, the first mammalian alkaline ceramidase to be identified as being specific for the hydrolysis of phytoceramide.

Longer breast-feeding and protection against childhood leukaemia and lymphomas.

The role of breast-feeding in protecting against childhood acute leukaemia and lymphomas is uncertain. We investigated this issue in a case-control study comprising 117 patients, aged 2-14 years, with acute lymphocytic leukaemia (ALL), Hodgkin's (HL) and non-Hodgkin's lymphoma (NHL), as well as 117 controls matched for age, sex and ethnicity. Information was collected via a telephone interview of the mothers. The median duration of breast-feeding among patients was significantly shorter than among controls, 7 (range 0-23) and 10 (range 0-20) months, respectively (P<0.0001). Breast-feeding of 0-6 months' duration, when compared with feeding of longer than 6 months, was associated with increased odds ratios (OR) for ALL (OR=2.47, 95% confidence interval (CI) 1.17-5.25), HL (OR=3.75, 95% CI 0.80-18.69), NHL (OR=4.06, 95% CI 0.82-22.59), and overall (OR=2.79, 95% CI 1.54-5.05). In the patient group, there were a significantly higher number of children and people per family, and patients were of a higher birth order than controls. In multivariate analysis, breast-feeding duration continues to be an independent predictor of lymphoid malignancies (P=0.015). In conclusion, breast-feeding lasting longer than 6 months may protect against childhood acute leukaemia and lymphomas.

Lack of apoptosis of infiltrating cells as the mechanism of high susceptibility to EAE in DA rats.

Dark Agouti (DA) rats are highly susceptible to induction of Th-1-mediated autoimmunity disease, including experimental allergic encephalomyelitis (EAE). In contrast to other susceptible rat strains in which disease is induced only with encephalitogen emulsified in complete Freund's adjuvants (CFA), in DA rats EAE develops after injection of encephalitogen in incomplete Freund's adjuvants (IFA) or Titermax, putative Th-2 directed adjuvant. Lymph node cells derived from immunized DA rats and stimulated in vitro produce significantly more Interferon-gamma (IFN-gamma) than resistant Albino Oxford (AO) rats. However, cells derived from both strains produce large amounts of IL-10 but not IL-4. Immunized lymph node cells derived from EAE susceptible (AO x DA) F1 rats induce clinical signs of disease in sublethally irradiated parental DA but not AO rats. The pathohistology of the target tissue in these recipients clearly demonstrated infiltration of mononuclear cells in both parental strains. However, the number of CD4+ cells was significantly higher and number of apoptotic cells significantly lower in DA rats sacrificed 8 days after passive transfer. We postulate that in addition to higher IFN-gamma and TNF-alpha production, resistance to early apoptosis of the invading cells in the target tissue possibly due to lack of downregulation by TGF-beta leads to exceptional susceptibility to EAE in DA rats.

Effects of cations on ceramide-activated protein phosphatase 2A.

Characterization of ceramide-effector(s), which includes protein phosphatase 2A (PP2A) is an important prelude to understanding the molecular basis of sphingolipid-mediated biological effects such as cell growth, differentiation and apoptosis. Recently, the existence of a metal-dependent form of PP2A has been reported (Cai et al., 1995). In this study, we investigated the effects of metal ions and chelators on ceramide-activated PP2A (CAPP). Our study demonstrates that at 0.5 mM concentration, Mg2+ appears to have no significant effect on either basal or ceramide-stimulated phosphatase activities, whereas Ca2+ stimulated the basal phosphatase activity, but was inhibitory towards CAPP. Moreover, the divalent cations Cr2+, Mn2+, Fe2+, Ni2+, Cu2+ and Zn2+ were tested and all were found to be inhibitory towards both CAPP and basal phosphatase activities. By contrast, Cs+ and Li+ had almost no effect on CAPP, although both stimulated basal phosphatase activity. The effects of EDTA and EGTA were tested and it was observed that EDTA decreased CAPP activity in a dose-dependent fashion, but had no effect upon basal phosphatase activity. These results suggest that CAPP is a metal-dependent protein, but, because Ca2+ inhibitied CAPP and EGTA was much less potent than EDTA in inhibiting CAPP, Ca2+ is unlikely to be its metal cofactor.

Proteolytic cleavage of phospholipase C-gamma1 during apoptosis in Molt-4 cells.

Apoptosis is a cell suicide mechanism that requires the activation of cellular death proteases for its induction. We examined whether the progress of apoptosis involves cleavage of phospholipase C-gamma1 (PLC-gamma1), which plays a pivotal role in mitogenic signaling pathway. Pretreatment of T leukemic Molt-4 cells with PLC inhibitors such as U-73122 or ET-18-OCH(3) potentiated etoposide-induced apoptosis in these cells. PLC-gamma1 was fragmented when Molt-4 cells were treated with several apoptotic stimuli such as etoposide, ceramides, and tumor necrosis factor alpha. Cleavage of PLC-gamma1 was blocked by overexpression of Bcl-2 and by specific inhibitors of caspases such as Z-DEVD-CH(2)F and YVAD-cmk. Purified caspase-3 and caspase-7, group II caspases, cleaved PLC-gamma1 in vitro and generated a cleavage product of the same size as that observed in vivo, suggesting that PLC-gamma1 is cleaved by group II caspases in vivo. From point mutagenesis studies, Ala-Glu-Pro-Asp(770) was identified to be a cleavage site within PLC-gamma1. Epidermal growth factor receptor (EGFR) -induced tyrosine phosphorylation of PLC-gamma1 resulted in resistance to cleavage by caspase-3 in vitro. Furthermore, cleaved PLC-gamma1 could not be tyrosine-phosphorylated by EGFR in vitro. In addition, tyrosine-phosphorylated PLC-gamma1 was not significantly cleaved during etoposide-induced apoptosis in Molt-4 cells. This suggests that the growth factor-induced tyrosine phosphorylation may suppress apoptosis-induced fragmentation of PLC-gamma1. We provide evidence for the biochemical relationship between PLC-gamma1-mediated signal pathway and apoptotic signal pathway, indicating that the defect of PLC-gamma1-mediated signaling pathway can facilitate an apoptotic progression.

Proto-oncogene ras GTPase-linked induction of glutathione-S-transferase by growth factors in PC12 cells.

This report provides evidence linking activation of Ras GTPase by growth factors and induction of glutathione-S-transferase isozymes in PC12 cells. Ras GTPase was activated by EGF, NGF, insulin and phorbolester in PC12 cells. Activation of Ras GTPase was found to be associated with induction of the expression of GST mu and pi isoenzymes while there was no detectable induction of GST alpha expression. GST pi was found to be induced by all the Ras GTPase activating agents tested while activation of Ras by phorbolester and insulin induced expression of GST mu only. These results suggest a role of Ras, at least in part, in controlling the expression of GST and that there might be independent signalling pathways for the expression of different GST isoenzymes. GST activity was found to be very high (4-fold) in the lysate obtained from retinoic acid treated PC12 cells when compared with untreated cells. Induction of GST expression was found to be initiated within 30 min of retinoic acid treatment in PC12 cells reaching a maximum level at 4 h. However, immunoblot analysis showed that retinoic acid (RA), unlike mitogens/growth factors, weakly induced the expression of GST pi but not the expression of alpha, mu and microsomal GSTs. Overxpression of inhibitory polypeptides that block signals generated from Ras and Cdc42 was found to reverse the retinoic acid activation-dependent induction of GST expression in PC12 cells. These results provide evidence for the first time suggesting a novel role of Ras GTPase in the regulation of GST expression which might have a significant implication in developing drug resistance and/or growth of cancer cells.

Purification and characterization of ceramide-activated protein phosphatases.

Ceramide has emerged as a potential regulator of diverse cellular functions, and a few direct targets have been identified for its action including protein kinases and phosphatases. In this study, we have purified the predominant ceramide-activated protein phosphatase (CAPP) from rat brain. Utilizing a novel chromatographic approach, CAPP was purified to near homogeneity using hydrophobic interaction chromatography on phenyl Sepharose followed by anion-exchange chromatography on MonoQ. The purified protein was composed of three major bands on SDS-polyacrylamide gel electrophoresis which comigrated with the three subunits of heterotrimeric PP2A. Immunologic studies further identified CAPP to be composed predominantly of heterotrimeric AB'C and ABalphaC as well as heterodimeric PP2A (AC), where C is the catalytic subunit, and A and B are regulatory subunits. These results were also supported by the coelution of CAPP with trimeric and dimeric PP2A on size-exclusion chromatography. These studies provide a convenient and efficient method for the isolation of trimeric and dimeric PP2A, and they allow the biochemical investigation of CAPP.

Src homology domains of phospholipase C gamma1 inhibit nerve growth factor-induced differentiation of PC12 cells.

Phospholipase C gamma1 (PLC-gamma1) is phosphorylated on treatment of cells with nerve growth factor (NGF). To assess the role of PLC-gamma1 in mediating the neuronal differentiation induced by NGF treatment, we established PC12 cells that overexpress whole PLC-gamma (PLC-gamma1PC12), the SH2-SH2-SH3 domain (PLC-gamma1SH223PC12), SH2-SH2-deleted mutants (PLC-gamma1deltaSH22PC12), and SH3-deleted mutants (PLC-gamma1deltaSH3PC12). Overexpressed whole PLC-gamma1 or the SH2-SH2-SH3 domain of PLC-gamma1 stimulated cell growth and inhibited NGF-induced neurite outgrowth of PC12 cells. However, cells expressing PLC-gamma1 lacking the SH2-SH2 domain or the SH3 domain had no effect on NGF-induced neuronal differentiation. Overexpression of intact PLC-gamma1 resulted in a threefold increase in total inositol phosphate accumulation on treatment with NGF. However, overexpression of the SH2-SH2-SH3 domain of PLC-gamma1 did not alter total inositol phosphate accumulation. To investigate whether the SH2-SH2-SH3 domain of PLC-gamma1 can mediate the NGF-induced signal, tyrosine phosphorylation of the SH2-SH2-SH3 domain of PLC-gamma1 on NGF treatment was examined. The SH2-SH2-SH3 domain of PLC-gamma1 as well as intact PLC-gamma1 could be tyrosine-phosphorylated on NGF treatment. These results indicate that the overexpressed SH2-SH2-SH3 domain of PLC-gamma1 can block the differentiation of PC12 cells induced by NGF and that the inhibition appears not to be related to the lipase activity of PLC-gamma1 but to the SH2-SH2-SH3 domain of PLC-gamma1.

Priming and induction of anti-rotavirus antibody response by synthetic peptides derived from VP7 and VP4.

Synthetic peptides derived from bovine rotavirus C-486 (BRV) outer capsid (VP7 and VP4) and inner capsid (VP6) proteins were tested to evaluate their ability to prime and induce an anti-rotavirus antibody response. Peptides corresponding to the amino acid residues 232-255 of VP4 (VP4-peptide), 275-295 of VP7 (VP7-peptide) and 40-60 of VP6 (VP6-peptide) of BRV were chemically synthesized. These peptides were coupled to carrier proteins (either keyhole limpet haemocyanin (KLH) or recombinant rotavirus inner capsid protein-VP6 assembled into virus-like particles (VP6-carrier) were used as carrier to link the synthetic peptides under study), and the resulting conjugates were used to immunize rotavirus seronegative mice. An enzyme-linked immunosorbent assay (ELISA) was used to determine anti-peptide and anti-rotavirus antibody titres in serum samples collected after immunization. All peptides were immunogenic in mice and induced the production of anti-peptide antibodies, but with the exception of VP6-peptide they were not able to induce anti-rotavirus antibodies as measured by ELISA. Western blot analysis indicated that antibodies against each peptide were able to react with the respective authentic viral proteins of various rotavirus serotypes. To determine if a peptide-primed animal would respond to native viral proteins, animals were subsequently injected with purified BRV. A rapid and high anti-rotavirus antibody titre, in addition to a rise in anti-peptide antibody titre, was observed in peptide-primed mice. Furthermore, the sera obtained from these mice neutralized the virus under in vitro conditions. The significance of these results in relation to a potential rotavirus synthetic peptide-based vaccine is discussed.

Studies on the rate of selective uptake of amino acids by Trichinella larvae in vivo.

Groups of C57BL/6J mice, orally infected with 300 larvae each of Trichinella spiralis or T. pseudospiralis were injected with [3H]-alanine, tyrosine, tryptophan or glycine. The incorporation of isotope labelled amino acids into larval proteins was measured at 2, 6, and 12 months post-infection. It was shown that there is a significant increase in the in vivo uptake of isotope labelled amino acids with time by the larvae of T. spiralis and T. pseudospiralis. The level of uptake was highest for tyrosine followed by tryptophan, alanine and then glycine, for both species. The in vivo uptake of amino acids by T. pseudospiralis larvae was always higher than T. spiralis or the host at 6 and 12 months post-infection. At 2 months post-infection, T. spiralis uptake of these amino acids was higher, except for tyrosine. This may be related to the special needs of these larvae during the process of encystation. The higher metabolic requirements of T. pseudospiralis may be related to the higher energy needs of these non encapsulated, highly motile and mobile muscle larvae.

The effect of a cAMP analogue on Ca2+ ionophore-, antigen- and agonist-induced inositol phosphate release in rat basophilic leukaemia (RBL-1) cells.

The effect of the stable cAMP analogue 8-Br-cAMP on leukotriene D4 (LTD4)-, 5'-N-ethyl-carboxamidoadenosine (NECA)-, antigen- and Ca2+ ionophore-induced inositol phosphate (IP) production was studied in RBL-1 cells. The cAMP analogue significantly inhibited LTD4- and antigen induced-IP production, thus supporting the hypothesis of a negative interaction between cAMP and phosphoinositide breakdown in blood cells. Ionophore-induced IP release, which was blocked by a 5-lipoxygenase inhibitor and by a LT-receptor antagonist, and therefore is probably mediated by LTs, was also inhibited by 8-Br-cAMP. NECA-induced IP release was not significantly inhibited by the cyclic nucleotide, thus showing that the effect described herein is not a general action on receptor-activated phospholipase C. 8-Br-cAMP did, however, inhibit GTP gamma S-induced IP release in permeabilised RBL-1 cells, thus suggesting that the inhibition does not occur at the receptor level but might be due, at least in part, to an effect on some receptor-coupled G proteins.

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.

Novel interactions between second messengers in rat basophilic leukaemia (RBL-1) cells.

As a continuation of our efforts to understand leukotriene biosynthesis mechanisms, we have studied the effect on RBL-1 cells of a series of phospholipase C (PLC) and phospholipase A2 (PLA2) activators including calcium ionophore (A23187), leukotriene D4 (LTD4), PAF, fMLP and bradykinin. LTD4 and A23187 (the latter only at 20 microM concentration and only after a 45 min incubation time) were shown to induce phosphoinositide (PI) breakdown, whilst A23187 induced leukotriene biosynthesis. For the first time it was shown that cAMP analogues markedly inhibit LTD4-induced IP formation. Moreover, the 5-lipoxygenase inhibitor AA861 abolished the ionophore-induced PI breakdown, thus suggesting that this effect is a novel example of PLC activation following PLA2 activation and 5-lipoxygenase-derived metabolite production.

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.