Responses of human dermal microvascular endothelial cells to histamine and their modulation by interleukin 1 and substance P.

The action of histamine on human dermal microvascular endothelial cells and modulation of its effects by the cytokine interleukin-1 and the vasoactive neuropeptide substance P have been investigated. Histamine (10(-6)-10(-3) M) induces release of prostaglandin E2 in a concentration- and time-dependent manner. Prostaglandin E2 release is facilitated principally by histamine H1 receptors as the H1 receptor antagonist pyrilamine attenuates prostaglandin E2 release whereas the H2 receptor antagonist cimetidine only slightly reduces release. In contrast to other cells, the histamine/receptor interaction is not associated with increased intracellular accumulation of the cyclic nucleotides, cyclic AMP, or cyclic GMP. Interleukin-1 induces a concentration-dependent release of prostaglandin E2 following 24 h incubation. However, substance P does not increase release of prostaglandin E2 above baseline. In cells incubated with 1 U/ml human recombinant interleukin 1 alpha for 24 h prior to stimulation with histamine (10(-5)-10(-3) M) for 30 min, there is a significant potentiation of histamine-induced release of prostaglandin E2 (p less than 0.05). Using a solubilized cell sonicate prepared from human dermal microvascular endothelial cells incubated with 1 U/ml human recombinant interleukin 1 alpha for 24 h, conversion of exogenous arachidonic acid into prostaglandin E2 increased by 60.19 +/- 18.28%. Cycloheximide partially reduces the increased conversion but completely blocks interleukin-1-induced release of prostaglandin E2 from intact cells. Substance P does not potentiate histamine-induced release of prostaglandin E2 or increase arachidonic acid conversion. These results demonstrate that human dermal microvascular endothelial cells are responsive to histamine and that interleukin-1, but not substance P, can potentiate histamine-induced release of prostaglandin E2. Interleukin-1 appears to act, at least in part, by regulating the availability of free arachidonic acid. Interactions between histamine and interleukin-1 may be important in the modulation of inflammatory reactions in skin.

Digital cutaneous vascular responses to histamine and neuropeptides in Raynaud's phenomenon.

The pathophysiology of Raynaud's phenomenon is not well defined, but active cutaneous microvascular vasoconstriction and emptying must occur to account for the pallor and are reasons for studying the microvasculature. It has been proposed that there may be a defect in a local histamine vasodilator mechanism. The role of the peptidergic nervous system in Raynaud's phenomenon has not been previously investigated. To study the histaminergic and peptidergic axes in Raynaud's phenomenon, we measured the cutaneous microvascular responses of patients with Raynaud's phenomenon to digital intradermal injections of saline, histamine, the histamine-releasing agent, compound 48/80, substance P, and calcitonin gene-related peptide. We compared these results with those obtained in normal subjects. Intradermal cutaneous microvascular blood flow responses were quantified by planimetry and laser Doppler flowmetry. The results show: a) that in primary Raynaud's phenomenon there is no evidence of local deficiency in histamine release or insensitivity to histamine in the cutaneous microvasculature; and b) that patients with Raynaud's phenomenon react normally to the neuropeptides calcitonin gene-related peptide and substance P, providing a rationale for treating Raynaud's phenomenon with vasoactive peptides.

12-Hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) does not stimulate proliferation of human neonatal keratinocytes.

We have developed an assay to study the effect of drugs on the proliferation of neonatal human skin-derived keratinocytes in vitro. Expanding populations of neonatal keratinocytes were cultured in low concentrations (0.5%) of fetal calf serum for up to 12 d. Growth of the cultures was determined by measurement of DNA using a sensitive fluorimetric assay. Addition of 10(-9)-10(-6) M 12(RS)-hydroxy-5,8,10,14-eicosatetraenoic acid (12(RS)-HETE) neither stimulated keratinocyte proliferation nor enhanced the incorporation of [3H]thymidine. The ability of neonatal keratinocytes in low serum medium to respond to exogenous factors was demonstrated by increased growth in response to a mixture of cholera toxin, hydrocortisone, and epidermal growth factor. Confluent keratinocyte cultures in 10% human AB serum exposed to 12(S)-HETE for 72 h also showed no changes in DNA, [3H]thymidine incorporation, or labeling index. Metabolism of 12(S)-[3H]HETE was greater in cultures containing low concentrations of serum but there was no evidence for the formation of 12,20-dihydroxyeicosatetraenoic acid.

Serum from patients with Raynaud's phenomenon inhibits prostacyclin production.

Prostacyclin (PGI2) and PGE2, the predominant cyclooxygenase products of endothelial cells are potent vasodilators. An inability to produce appropriate concentrations of these prostanoids may be a factor in the pathogenesis of the digital vasospasm experienced by patients with Raynaud's phenomenon (RP). The effect of sera from normal subjects, patients with primary RP, and patients with RP in association with systemic sclerosis (SS) on the production of PGI2 and PGE2 by cultured human endothelial cells was investigated. All sera produced a dose-dependent inhibition of 6-keto-PGF1 alpha, but both the 10% and 20% sera from patients with RP and SS produced a significantly greater inhibition than control sera. The mean production of 6-keto-PGF1 alpha expressed in ng/10(4) cells was 2.278 (normal), 1.9311 (RP), and 2.1824 (SS) after incubation with 1% serum for 24 h. This decreased to 1.3647, 0.5927, and 0.4171, respectively following incubation with 20% sera for 24 h. This represented a 44% (normal), 76% (RP), and 83% (SS) inhibition of 6-keto-PGF1 alpha production compared with serum free media. Similar results were obtained after 1 h incubation experiments. There was a nonsignificant decrease in mean PGE2 production following similar incubations with 1% and 20% sera for 24 h. These results suggest that factor(s) present in the sera of patients with RP may reduce the ability of endothelial cells to synthesize or release the vasodilator and antiaggregatory prostanoid PGI2.

Neuropeptides induce release of nitric oxide from human dermal microvascular endothelial cells.

Nitric oxide is a potent mediator of endothelium-dependent vasodilation, the synthesis of which is catalyzed by the constitutively expressed enzyme endothelial nitric oxide synthase. In this study we have investigated whether human dermal microvascular endothelial cells express endothelial oxide synthase and whether the vasodilator neuropeptides, calcitonin gene-related peptide and substance P, stimulate the release of nitric oxide from these cells. Endothelial nitric oxide synthase was identified by immunohistochemistry in the blood vessels in both the papillary and deep dermis of normal skin, and also in monolayers of human dermal microvascular extracts prepared from both the dermis of normal human skin and human dermal microvascular endothelial cells, a 135-kDa band corresponding to endothelial nitric oxide synthase was identified. Nitric oxide was released from unstimulated human dermal microvascular endothelial cells as assessed by inhibition of platelet aggregation and nitrate formation. Endothelial cell-mediated inhibition of platelet aggregation was blocked by hemoglobin. Calcitonin gene-related peptide, (100 pM to 100 nM) directly inhibited platelet aggregation, and this direct effect was not modulated by microvascular endothelial cells. Substance P (10 nM to 1 muM) and calcitonin gene-related peptide (100 pM to 10 nM) significantly (p<0.05) increased nitrite formation, and this increase was blocked by the competitive nitric oxide synthase antagonist, NG-monomethyl-L-arginine. These results demonstrate that endothelial nitric oxide synthase is expressed in the microvascular endothelium of normal human skin and that human dermal microvascular endothelial cells release nitric oxide constitutively and in response to vasodilator neuropeptides.

Cutaneous responses to endothelin-1 and histamine in patients with vibration white finger.

Vibration white finger (VWF) is the episodic blanching of the fingers that occurs in response to cold in those who work with hand-held vibrating tools. Clinically the condition differs from primary Raynaud's phenomenon as persistent pain and paresthesia are common in the hands and arms and occur independently of the "white attacks." We have previously reported a decrease in protein gene product 9.5 and calcitonin gene-related peptide-immunoreactive nerve fibers in the digital skin of individuals with VWF. In this study, we have sought to determine whether this deficit of immunoreactive sensory-motor nerves has a functional counterpart in vivo. Histamine produces a rapid wheal and flare response following intradermal injection, whereas endothelin-1 (ET-1) produces a central area of pallor with a surrounding neurogenic flare. In contrast, calcitonin gene-related peptide produces a non-neurogenic erythema. In this study, histamine and ET-1 were injected into the dorsum of the middle phalanx and the local neurovascular response was assessed by measuring the area of the visible flare or pallor. Basal finger blood flow was also measured by laser Doppler flowmetry in each of the digits prior to intradermal injection. The experiments were performed at 21 degrees C and 4 degrees C. Patients with VWF and asymptomatic vibration-exposed workers had significantly lower resting skin blood flow at both 21 degrees C and 4 degrees C than heavy manual workers with no vibration exposure. The size of the histamine- and ET-1-induced flares at both 21 degrees C and 4 degrees C was significantly smaller in patients with VWF when compared with the asymptomatic vibration-exposed workers and heavy manual workers. The size of the ET-1-induced pallor was smaller in patients with VWF when compared with the heavy manual workers at both 21 degrees C and 4 degrees C. In contrast, the area of erythema induced by intradermal injection of calcitonin gene-related peptide at both 21 degrees C and 4 degrees C was of a similar size in patients with VWF and in heavy manual workers. These results indicate that the neuroneal deficit identified by immunohistochemistry in the digital skin of patients with VWF has a functional counterpart in vivo and is evident as a reduced ability to propagate an axon-reflex vasodilator response when challenged with histamine and ET-1. Furthermore, these results enable patients with VWF to be differentiated from both asymptomatic vibration-exposed workers, in whom the histamine- and ET-1-induced flares are normal, and those with primary Raynaud's disease, in whom the ET-1 flare is reduced and the histamine-induced flare is normal.

Cutaneous responses to 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE).

The responses to 12-HETE in normal human skin have been investigated by means of intradermal and topical administration in 15 subjects. Intradermal infusion of 12-HETE produced a neutrophil polymorphonuclear and mononuclear infiltrate in the dermis. Topical administration resulted in a dose-related erythematous response to 200 ng-50 micrograms. This was accompanied by a neutrophil and mononuclear dermal infiltrate at 6 and 24 h after application. In addition, collections of neutrophils were present in the epidermis in 4 of 10 subjects biopsied at 6 h and in all patients biopsied 24 h after topical application. Intradermal and topical application of 9-hydroxyoctadecadienoic acid (9-HODD), a chemically similar but chemokinetically inactive substance, did not produce neutrophil infiltration of the epidermis, nor did the chemical irritant nonanoic acid. The results suggest that the cellular infiltrates produced in vivo in humans by 12-HETE are due to its chemoattractant properties and are not the result of a nonspecific inflammatory response.

Blood mononuclear cells from patients with psoriasis exhibit an enhanced adherence to cultured vascular endothelium.

Blood mononuclear cells (MNC) from patients with psoriasis were more adherent to monolayers of endothelial cells prepared from human umbilical cord vein than otherwise similar cells from control subjects. This increase in adherence occurred in the presence (mean 37% increase; p less than 0.01) and absence (mean 47% increase; p less than 0.05) of 10% autologous serum and was not related to the disease severity of the patients. The augmented adhesiveness of the patients' cells was also apparent when using monolayers of endothelial cells isolated from human skin. The levels of immune complexes, complement, alpha 2-macroglobulin, acute phase proteins (alpha 1-acid glycoprotein, C-reactive protein and alpha 1-antitrypsin), and tumor necrosis factor alpha (TNF alpha), interleukin-1 alpha (IL-1 alpha), and interleukin-1 beta (IL-1 beta) in the patients' sera were within normal limits. When MNC were added to endothelial monolayers that had been incubated with either TNF alpha or the highest concentration of rIL-1 beta used in the study, both the patients' and control's cells exhibited a similar increase in attachment (p less than 0.01). Pretreatment of endothelium with interferon-gamma did not enhance the attachment of MNC from either group of subjects. The augmented adherence of the patient's MNC appears to be due to an abnormal adhesiveness of the lymphocytes rather than the monocytes and is not related to an enhanced expression of the cell-surface adhesion molecules CD11a/CD18. It is likely that the circulating MNC of psoriatic patients may be predisposed for extravasation into skin.

Characterization of endothelin-binding sites in human skin and their regulation in primary Raynaud's phenomenon and systemic sclerosis.

Endothelin (ET), which mediates vasoconstrictor and vasodilator activities via multiple receptor subtypes, has been implicated in the control of blood flow and vascular tone in human skin, and possibly in the abnormal vasoconstrictor response in primary Raynaud's phenomenon and systemic sclerosis. Using in vitro autoradiography we have examined the endothelin-binding characteristics and receptor subtypes of human skin, and sought to provide evidence for endothelin receptor regulation in skin from patients with primary or secondary Raynaud's phenomenon. Specific 125I-ET-1 and 125I-ET-3 binding sites were localized to microvessels of the sub-epidermal plexus and dermal papillae, larger blood vessels, sweat glands, epidermis, and hair follicles. Both ETA and ETB receptors were demonstrated in microvessels and other structures. ET receptor heterogeneity in skin vasculature suggests a role for ET as an autocrine/paracrine regulator of vasoconstrictor and vasodilator pathways in human skin. The presence of binding sites in epidermis and hair follicles suggests a possible mitogenic function for endothelin in human skin. Endothelin-binding density was significantly higher (p < 0.05) in microvessels of skin from patients with systemic sclerosis but not significantly different in Raynaud's phenomenon patients, compared to controls. Lack of down regulation of ET receptors in Raynaud's phenomenon and systemic sclerosis may contribute to the pathogenesis of vasospasm in these diseases.

Basophil mediator release in atopic dermatitis.

Basophils have been implicated as a source of histamine and pro-inflammatory eicosanoids in atopic dermatitis. However, mechanisms regulating basophil mediator release are not understood. An H3 receptor involved in the control of histamine synthesis and release has been identified in nervous tissue. In this study we have investigated 1) release of histamine, leukotriene C4, and prostaglandin D2 from anti-immunoglobulin E (IgE)-stimulated basophils of adults with atopic dermatitis and unaffected individuals and 2) specific H3 receptor-dependent basophil mediator release, using an H3 receptor agonist and antagonist. Basophil-rich leukocyte fractions were prepared by dextran sedimentation of venous blood from 19 patients with atopic dermatitis (five male, 14 female, mean age 30.6 years, range 19-59 years) and 15 unaffected individuals (five male, 10 female, mean age 27.6 years, range 19-50 years). Anti-IgE (0.78-78.0 micrograms/ml) stimulation of basophils induced a concentration-dependent release of histamine and leukotriene C4, but not prostaglandin D2. Histamine release was maximally induced by 7.8 micrograms/ml anti-IgE with no significant (Mann-Whitney U test) difference between atopic basophils (n = 17; 43.65 +/- 4.16% mean +/- SEM) and normal basophils (n = 13; 52.23 +/- 4.39%). LTC4 release was maximal from atopic basophils incubated with 2.6 micrograms/ml anti-IgE (n = 5; 0.99 +/- 0.29 pg/10(6) cells) and from normal basophils incubated with 0.78 microgram/ml anti-IgE (n = 5; 25.38 +/- 5.79 pg/10(6) cells). Anti-IgE-stimulated release of leukotriene C4 from atopic basophils was significantly less than from normal basophils at all concentrations (p < 0.05). Basophils were co-incubated with anti-IgE (2.6 and 7.8 micrograms/ml) and either the H3 receptor agonist, (R)alpha-methylhistamine (10(-8) and 10(-7) M), or the H3 receptor antagonist thioperamide (10(-6) and 10(-5) M). Neither drug modulated anti-IgE-induced release of histamine (atopics, n = 10; normals, n = 8). These results indicate 1) that basophils from adults with atopic dermatitis release the same amount of histamine as, but less leukotriene C4 than, basophils of unaffected adults and 2) that H3 receptors are not involved in anti-IgE release of histamine from basophils. These data do not support a role for increased basophil release of histamine as a mediator in the itch and erythema of atopic dermatitis in adults.

Effects of the lupus anticoagulant in patients with systemic lupus erythematosus on endothelial cell prostacyclin release and procoagulant activity.

A disturbance in endothelial cell (EC) function may be pathogenetic in the thrombotic tendency of patients with the lupus anticoagulant (LA). The ability of serum from normal subjects and patients with systemic lupus erythematosus (SLE), with and without the LA, to modulate the release of prostacyclin (PGI2) and the expression of procoagulant activity by cultured human EC was investigated. Only the 10% and 20% serum concentrations from patients with SLE-LA produced a significantly greater inhibition of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) release (the stable metabolite of PGI2) than control serum. However, when patients with SLE-LA having Raynaud's phenomenon were excluded from this group, there was then no significant difference between the effect of the patient and control serum. Serum from patients with SLE +/- LA caused a significant increase in EC procoagulant activity compared to healthy controls. The two-stage partial thromboplastin time expressed in seconds decreased from 66 (normal) to 34 (SLE - LA) and 31 (SLE + LA), but there was no significant difference between the patients with and without the LA. The significantly increased EC procoagulant activity induced by serum from patients with SLE +/- LA may account for the observed increased incidence of thrombotic events in patients with SLE. Our data suggest that factors other than decreased prostacyclin release are responsible for the altered hemostasis observed in patients with SLE + LA.

Inhibitors of nitric oxide synthase in human skin.

The aim of this study was to investigate in human skin in vivo the role of nitric oxide in maintaining resting vascular tone, in the vasodilatation caused by local warming and by ultraviolet B light exposure, and in the response to exogenous calcitonin gene-related peptide (CGRP). Cutaneous blood flow was assessed by planimetry of the visible erythema or pallor and by laser Doppler flowmetry. Intradermal injection of the inhibitor of nitric oxide synthase, NG-nitro-L-arginine methyl ester (L-NAME; 25 nmol), into forearm skin produced a visible pallor and a reduction of blood flow at a controlled ambient temperature of 21 degrees C. The control, NG-nitro-D-arginine methyl ester (D-NAME; 25 nmol) or NG-monomethyl-L-arginine (L-NMMA; 25 nmol) did not cause pallor or reduce blood flow. L-NAME and L-NMMA caused dose- and time-dependent increases in pallor, and reductions in cutaneous blood flow in skin that had been locally warmed by immersion in water at 45 degrees C and in skin that had been exposed to ultraviolet B light. D-NAME and D-NMMA at comparable concentrations did not have the effects on skin blood flow observed with the L forms. L-NAME and L-NMMA both inhibited the increased blood flow in human skin caused by the intradermal injection of CGRP (12.5 or 25 pmol). The reduction of CGRP-induced increase of blood flow by L-NAME was reversed by L-arginine. Neither D-NAME nor D-NMMA inhibited the increase in blood flow caused by CGRP. Neither L-NAME nor L-NMMA inhibited the increase in blood flow in human skin caused by the intradermal injection of prostaglandin E2 (63 pmol). The data show that nitric oxide is involved in the maintenance of resting blood flow in human skin and also in the cutaneous vasodilator responses to local warming, ultraviolet B irradiation, or injection of CGRP.

Endothelin-1 in human skin: immunolocalization, receptor binding, mRNA expression, and effects on cutaneous microvascular endothelial cells.

Endothelin-1 (ET-1), a potent vasoconstrictor peptide, has been implicated in the maintenance of systemic and peripheral vascular tone. We have therefore sought direct evidence of a role for ET-1 in the regulation of blood flow and vascular tone in the human cutaneous microvasculature. Immunostaining for ET-1 was observed in all cutaneous blood vessels of normal human skin including the capillaries of the dermal papillae. Autoradiography showed specific binding of 125I-ET-1 over capillaries and larger blood vessels as well as hair follicles and sweat glands. In situ hybridization with a 32P-labeled RNA probe for ET-1 demonstrated mRNA for ET-1 in cultured human dermal microvascular endothelial cells (HDMEC). In HDMEC, basal release of PGE2 was significantly attenuated by ET-1 (100 pM-100 nM) (p less than 0.05, n = 7) with maximum inhibition in cells incubated with 10 nM ET-1. ET-1 also increased intracellular cAMP in a dose-dependent manner with a significant increase in HDMEC incubated with 100 nM ET-1 (p less than 0.05, n = 4). In HDMEC incubated with 100 nM ET-1, inhibition of PGE2 release was unaffected by the dihydropyridine Ca++ channel antagonist nifedipine or the extracellular Ca++ chelator EGTA, whereas the intracellular Ca++ chelator TMB-8 partially blocked the action of ET-1. In contrast, cAMP accumulation was significantly attenuated by EGTA (p less than 0.05, n = 4), nifedipine (p less than 0.05, n = 4), and TMB-8 (p less than 0.05, n = 4), indicating that the endothelial cell responses to ET-1 are complex and appear to involve both Ca(++)-sensitive and -insensitive pathways. These results provide evidence of an autocrine/paracrine role for ET-1 in the human cutaneous microvasculature.

Src-related protein tyrosine kinases are physically associated with the surface antigen CD36 in human dermal microvascular endothelial cells.

Src-related cytoplasmic PTKs are physically and functionally associated with cell surface receptors and are involved in signal transduction. In this paper we report the identification of src-related proteins p59fyn, pp60c-src and p62yes in human microvascular endothelial cells cultured from normal human skin and their physical association with the thrombospondin receptor CD36. Such an association represents a potential signalling pathway by which thrombospondin may regulate angiogenesis.

Nerve growth factor contributes to the up-regulation of growth-associated protein 43 and preprotachykinin A messenger RNAs in primary sensory neurons following peripheral inflammation.

Peripheral inflammation induced in adult rats by an intraplantar injection of complete Freund's adjuvant results in a rapid (6 h) increase in the expression of the messenger RNAs for the neuronal growth-associated protein 43 and for preprotachykinin A, the precursor for substance P, in dorsal root ganglion sensory neurons innervating the inflamed area. This increase peaks at 48 h and then declines by five days. The changes are present in the dorsal root ganglion cells innervating the inflamed skin (lumbar 4 or 5) but no elevation was found in the third lumbar dorsal root ganglion which innervates neighbouring non-inflamed skin. The increased growth-associated protein 43 messenger RNA in the dorsal root ganglion is followed by a marked increase in growth-associated protein 43-like immunoreactive fibres in the epidermis of the inflamed skin. Systemic administration of neutralizing anti-nerve growth factor antibodies immediately prior to the inflammation prevents the increase in growth-associated protein 43 and preprotachykinin A messenger RNAs in the sensory neurons. A subcutaneous injection of nerve growth factor (200 ng) into the hindpaw elevates preprotachykinin A but not growth-associated protein 43 messenger RNA in the fourth lumbar dorsal root ganglion 48 h post-injection and this could be prevented by co-administration of the anti-nerve growth factor serum. The production of nerve growth factor in inflamed target tissues leads to alterations in the phenotype of responsive adult primary sensory neurons which include a change in the levels of a growth-related protein and a peptide neuromodulator.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 potentiates histamine-induced release of prostacyclin from human endothelial cells.

1. In human cultured umbilical vein endothelial cells, interleukin-1 potentiated histamine-induced release of prostacyclin in a time- and concentration-dependent manner. 2. In cells incubated with interleukin-1 for 24 h, maximal potentiation was observed when cells were pre-incubated with 0.5 u ml-1 interleukin-1 before stimulation with histamine (1 microM-1 mM). 3. In cells incubated with 0.5 u ml-1 interleukin-1, 20 min pre-incubation was sufficient to induce a statistically significant potentiation of prostacyclin release induced by 1 microM histamine (P less than 0.05). 4. Nifedipine but not cycloheximide, significantly (P less than 0.05) inhibited histamine-induced release of prostacyclin and interleukin-1 potentiation of histamine-induced release of prostacyclin (P less than 0.05). 5. Incubation with 1 u ml-1 interleukin-1 induced a two fold increase in cellular prostaglandin synthetase activity within 30 min. The enzyme activity increased up to 6 h and was maintained up to 24 h. In cells co-incubated with cycloheximide and 1 u ml-1 interleukin 1, prostaglandin synthetase activity at 24 h was the same as that in unstimulated cells. Prostacyclin release was not significantly inhibited in cells co-incubated with cycloheximide and interleukin 1. 6. These results suggest that interleukin-1 potentiates histamine-induced release of prostacyclin by rapid up-regulation of prostaglandin synthetase activity as well as by inducing synthesis of enzyme protein. These mechanisms may act to potentiate/regulate vascular endothelial responses in inflammatory reactions.

Characterization of histamine receptor sub-types regulating prostacyclin release from human endothelial cells.

1. The histamine receptor sub-types that are involved in the initiation and maintenance of prostacyclin (PGI2) release from human endothelial cells have been investigated. 2. Endothelial cells cultured from umbilical vein (HUVEC) were incubated with either histamine, the selective H1-receptor agonists, 2-methyl histamine (2-MeHA) or thiazolylethylamine (ThEA), the H1-agonist/H3-antagonist, beta-histidine (beta-His), the selective H2-agonist, dimaprit, the H2-agonist/H3-antagonist, impromidine, the selective H3-agonist, (R)alpha-methylhistamine ((R)alpha-MeHA) and the H3-antagonist, thioperamide. 3. The H1-agonists and the H3-agonist (R)alpha-MeHA induced a concentration (100 nM-1 mM) and time-dependent release of PGI2 as determined by radioimmunoassay for 6-keto-PGF1 alpha, but were less potent than histamine itself. The rank order of potency was the same following 30 min and 24 h incubation, i.e. histamine > ThEA > 2-MeHA >> beta-His > (R)alpha-MeHA. 4. Histamine and 2-MeHA (1 microM-1 mM), ThHEA (10 microM-1 mM) and (R)alpha-MeHA (1 mM), but not beta-His, induced a significantly greater increase in PGI2 release after 24 h incubation than after 30 min incubation (P < 0.05). 5. Neither the selective H2-agonist, dimaprit, nor the H2-agonist/H3-antagonist, impromidine alone induced release of PGI2. 6. The H1-antagonist, mepyramine (10 microM), abolished release of PGI2 induced by histamine, the H1-agonists and (R)alpha-MeHA but the H2-antagonist cimetidine (10 microM) and the H2/H3-antagonist, burimamide (10 microM) did not significantly modulate PGI2 release. 7. Although the H3-agonist (R)alphax-MeHA induced release of PGI2, it failed to modulate PGI2 release in the presence of histamine.8. Low concentrations of the H3-antagonist, thioperamide (100 nM) did not modulate histamine release of PGI2 at all but after 24 h incubation, thioperamide (10-4 M) partially reduced PGI2 release in the presence of histamine.9. These results indicate that PGI2 from HUVEC is initiated and maintained via histamine HI-receptor occupancy. There appears to be no involvement of either H2- or H3-receptors in this particular endothelial cell histaminergic response.

Leukotriene B4-like material in scale of psoriatic skin lesions.

Acidic lipid extracts of scale from the lesions of the skin disease, psoriasis, were purified by straight phase high performance liquid chromatography (h.p.l.c.). Assay of fractions by an agarose microdroplet chemokinesis method showed the presence of biologically active material that coeluted with standard leukotriene B4 (LTB4). LTB4-like chemokinetic activity was also detected in fractions collected on reversed phase h.p.l.c. of psoriatic scale extracts that were initially purified by straight phase h.p.l.c. No LTB4-like activity was detected after similar purification of scale obtained by abrasion of large areas of normal skin. The LTB4-like material found in extracts of psoriatic scale may play a role in the pathogenesis of the neutrophil infiltrate which characterizes psoriasis.

Cutaneous responses to 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) and 5,12-dihydroxyeicosatetraenoic acid (leukotriene B4) in psoriasis and normal human skin.

The arachidonate lipoxygenase products 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) and 5(S),12(R)-dihydroxy-6,8,10,14-eicosatetraenoic acid (leukotriene B4, LTB4) are potent leucocyte chemoattractants in vitro and in vivo. Both 12-HETE and LTB4-like material are found in increased amounts in lesional skin in psoriasis. Epicutaneous administration of 12(R,S)-HETE and LTB4 in normal skin evokes neutrophil and mononuclear dermal infiltrates accompanied by collections of neutrophils in the epidermis. Similar appearances result from the application of LTB4 to uninvolved skin in psoriasis. We have now investigated the effects of single and multiple epicutaneous applications of 12(R,S)-HETE and LTB4, both alone and in combination, in normal human skin and in clinically uninvolved skin of patients with psoriasis. As in the case of LTB4, erythematous responses to 12(R,S)-HETE were similar in normal skin and in psoriasis. Similar neutrophil polymorphonuclear responses were evoked by topical application of 50 ng LTB4 and 20 micrograms 12(R,S)-HETE. Application of the combination of 12(R,S)-HETE and LTB4 evoked only a partially additive erythematous response, and no evidence of an additive neutrophilotactic response was detected histologically. Multiple applications resulted in tolerance both clinically and histologically. Cross tolerance to 12(R,S)-HETE and LTB4 occurred in the majority of subjects. These results suggest that both 12(R,S)-HETE and LTB4 may be important in the production and control of the magnitude of the inflammatory events in psoriasis.

The new H1 antihistamines. Treatment of urticaria and other clinical problems.

The new H1 antihistamines are a major therapeutic advancement in the treatment of allergic disorders such as urticaria and allergic rhinitis. Their efficacy combined with greatly reduced sedating and anticholinergic side effects makes the new class of H1 antihistamines the first-line treatment in the management of urticaria and mild angioedema. The choice of a particular low-sedating H1 antihistamine depends on pharmacokinetic considerations, the severity of the problem (systemic steroids and epinephrine are the first-line treatment for severe angioedema), and the requirement for limiting the frequency of administration. The efficacy of the new H1 antihistamines in the treatment of itch due to atopic eczema and systemic disease remains uncertain, and further controlled clinical trials are needed to elucidate their possible role in these conditions.