Loop electrosurgical excision procedure for the treatment of cervical intraepithelial neoplasia: how much excision is enough?

This is a retrospective observational study to compare outcomes in patients with cervical intraepithelial neoplasia (CIN) treated with loop electrosurgical excision procedure (LEEP) using combined ectocervical/endocervical resection vs ectocervical resection alone. We demonstrated that additional endocervical resection during loop electrosurgical excision procedure did not significantly lower the risk of subsequent recurrence compared with ectocervical resection alone, in the treatment of CIN. With current published data supporting subsequent increased adverse effects of LEEP on future obstetrical outcomes, endocervical excision should be applied selectively. We recommend that additional endocervical excision should be reserved only for patients with a strong suspicion of underlying endocervical canal involvement based on colposcopic assessment or in patients with unsatisfactory colposcopy, where it is essential to evaluate the endocervical canal.

Live-cell three-dimensional single-molecule tracking reveals modulation of enhancer dynamics by NuRD.

To understand how the nucleosome remodeling and deacetylase (NuRD) complex regulates enhancers and enhancer-promoter interactions, we have developed an approach to segment and extract key biophysical parameters from live-cell three-dimensional single-molecule trajectories. Unexpectedly, this has revealed that NuRD binds to chromatin for minutes, decompacts chromatin structure and increases enhancer dynamics. We also uncovered a rare fast-diffusing state of enhancers and found that NuRD restricts the time spent in this state. Hi-C and Cut&Run experiments revealed that NuRD modulates enhancer-promoter interactions in active chromatin, allowing them to contact each other over longer distances. Furthermore, NuRD leads to a marked redistribution of CTCF and, in particular, cohesin. We propose that NuRD promotes a decondensed chromatin environment, where enhancers and promoters can contact each other over longer distances, and where the resetting of enhancer-promoter interactions brought about by the fast decondensed chromatin motions is reduced, leading to more stable, long-lived enhancer-promoter relationships.

The flavonoid luteolin inhibits niacin-induced flush.

BACKGROUND AND PURPOSE: Sustained release niacin effectively lowers serum cholesterol, LDL and triglycerides, while raising HDL. However, 75% of patients experience cutaneous warmth and itching known as flush, leading to discontinuation. Acetylsalicylic acid (aspirin) reduces this flush only by about 30%, presumably through decreasing prostaglandin D2 (PGD2). We investigated whether niacin-induced flush in a rat model involves PGD2 and 5-HT, and the effect of certain flavonoids. EXPERIMENTAL APPROACH: Three skin temperature measurements from each ear were recorded with an infrared pyrometer for each time point immediately before i.p. injection with either niacin or a flavonoid. The temperature was then measured every 10 min for 60 min. KEY RESULTS: Niacin (7.5 mg per rat, equivalent to a human dose of 1750 mg per 80 kg) maximally increased ear temperature to 1.9+/-0.2 degrees C at 45 min. Quercetin and luteolin (4.3 mg per rat; 1000 mg per human), administered i.p. 45 min prior to niacin, inhibited the niacin effect by 96 and 88%, respectively. Aspirin (1.22 mg per rat; 325 mg per human) inhibited the niacin effect by only 30%. Niacin almost doubled plasma PGD2 and 5-HT, but aspirin reduced only PGD2 by 86%. In contrast, luteolin inhibited both plasma PGD2 and 5-HT levels by 100 and 67%, respectively. CONCLUSIONS AND IMPLICATIONS. Niacin-induced skin temperature increase is associated with PGD2 and 5-HT elevations in rats; luteolin may be a better inhibitor of niacin-induced flush because it blocks the rise in both mediators.

Intravesical nanocrystalline silver decreases experimental bladder inflammation.

PURPOSE: Interstitial cystitis is a sterile bladder inflammatory disease characterized by pelvic pain, urinary urgency and frequency. Nanocrystalline silver has anti-inflammatory properties, prompting us to investigate its effect in experimental bladder inflammation. MATERIALS AND METHODS: Nanocrystalline silver (0.01%, 0.05%, 0.1%, 0.5% or 1%) or phosphate buffered saline (Invitrogen) (0.5 ml) was introduced intravesically in Sprague-Dawley female rat (Charles River Laboratories, Wilmington, Massachusetts) bladders for 20 minutes, followed by vehicle or protamine sulfate (10 mg/ml for 30 minutes) and lipopolysaccharide (Sigma) (2 mg/ml for 45 minutes). Urine was collected throughout for histamine assay. The catheter was removed, the rat was returned to its cage and 4 hours later it was sacrificed. The bladder was harvested, minced and cultured overnight. The medium was collected for tumor necrosis factor-alpha assay. RESULTS: Mean +/- SD total urine histamine increased from 270 +/- 190 ng in 4 controls to 842 +/- 239 ng after protamine sulfate/lipopolysaccharide and it decreased to 505 +/- 187 ng in 6 animals after pretreatment with 1% nanocrystalline silver (p = 0.036). Tumor necrosis factor-alpha release in explant medium increased from 0.02 +/- 0.03 pg/mg in 6 controls to 0.28 +/- 0.15 pg/mg in 14 animals after treatment with protamine sulfate/lipopolysaccharide and it decreased to 0.12 +/- 0.11 pg/mg in 10 animals pretreated with nanocrystalline silver (p = 0.009). Nanocrystalline silver was not effective at less than 1% and at 1% alone it released 0.05 +/- 0.07 pg/mg tumor necrosis factor-alpha in 7 rats (vs phosphate buffered saline in 6, p = 0.387). Nanocrystalline silver (1%) significantly decreased bladder inflammation and mast cell activation. These effects were apparent even 4 days later. CONCLUSIONS: Intravesical administration of nanocrystalline silver (1%) decreased urine histamine, bladder tumor necrosis factor-alpha and mast cell activation without any toxic effect. This action may be useful for interstitial cystitis.

Anti-chemokine therapy for inflammatory diseases.

Chemokines are inflammatory proteins acting via G-protein coupled chemokine receptors that trigger different signaling pathways. Monocyte chemoattractant protein-1 (CCL2/MCP-1) and regulated on activation, normal T expressed and secreted (CCL5/RANTES) are the two major members of the CC chemokine beta subfamily. The roles of RANTES and MCP-1 are emerging in regulating the recruitment of inflammatory cells into tissue during inflammation. The inhibition of MCP-1 and RANTES with corresponding antibodies or other inhibitors may provide benefits in different clinical scenarios including cancer, inflammation, CNS disorders, parasitic disease, autoimmune and heart diseases. RANTES and MCP-1 may represent targets for diagnostic procedures and therapeutic intervention, and may be useful as a prognostic factor in the above diseases.

Progesterone inhibits mast cell secretion.

Mast cells are involved in allergic reactions, where they secrete numerous vasoactive, inflammatory and nociceptive mediators in response to immunoglobulin E (IgE) and antigen. However, they have also been implicated in inflammatory conditions, such as painful bladder syndrome/interstitial cystitis (PBS/IC), irritable bowel syndrome (IBS) and migraines, all of which occur more often in women and are exacerbated during ovulation, but are suppressed during pregnancy. Mast cells express high affinity estrogen receptors and estradiol augments their secretion, while tamoxifen inhibits it. Here we report that progesterone (100 nM), but not the structurally related cholesterol, inhibits histamine secretion from purified rat peritoneal mast cells stimulated immunologically or by substance P (SP), an effect also documented by electron microscopy. These results suggest that mast cell secretion may be regulated by progesterone and may explain the reduced symptoms of certain inflammatory conditions during pregnancy.

IL-15 an immunoregulatory and anti-cancer cytokine. Recent advances.

Interleukins are mediators of inflammation, immunity and cancer. IL-15 is a cytokine produced by several leukocytes including phagocytes in response to infections and other signals that trigger innate immunity. IL-15 has many homologies to interleukin-2 (IL-2) and like IL-2, stimulates NK cells. This cytokine acts also on memory CD8+ T-cell. IL-15, therefore acts, probably through selective inhibition of tumor promoting molecules, as a new compound for the adjuvant treatment of solid tumors. In this review we propose a newly revised mechanism of interleukin 15 in inflammation and cancer.

C19-radiosteroid disposition in organ cultures of transplanted prostatic adenocarcinomas of the Noble rat.

This study compares the disposition of 8.5-nM C19-radiosteroids in 21-h cultures of Noble rat dorsolateral prostate (DLP) and transplanted adenocarcinomas derived from the DLP. Our purpose was to determine whether differences in androgen activation could be detected between the androgen-stimulated tumor (AST) line, an androgen-independent tumor line carried in intact (AIT-I) and castrated (AIT-C) rats and their DLP tissue of origin. No differences were found between DLP, AST, AIT-I, and AIT-C for the following parameters: 5 alpha-reduction of [3H]testosterone to dihydrotestosterone (DHT); however, conversion to total 5 alpha-reduced metabolites was lower in AIT-C than DLP cultures; explant retention of [3H]testosterone-derived DHT; tissue capacity to hydroxylate [3H]5 alpha-androstane-3 beta,17 beta-diol; total and nuclear high-affinity binding of [3H]DHT to salt-extractable explant protein, except for one AIT-C which yielded half the number of binding sites. Since AIT carried in either intact or castrated hosts is competent as regards formation, retention and high-affinity binding of [3H]DHT in organ culture, we conclude that the neoplasm possesses some of the characteristics considered essential for the expression of androgen responsiveness in vivo.

Theophylline as "add-on" therapy in patients with delayed pressure urticaria: a prospective self-controlled study.

Delayed pressure urticaria (DPU) is a skin condition that involves the gradual development of wheals and edema at sites of physical pressure. Its pathogenesis is not clear and histamine-1 receptor (H-1R) antagonists provide only partial relief. In this prospective, clinical study, we investigated the effect of theophylline, which has a long history of benefit in allergic asthma, added to cetirizine in patients with DPU. Twenty three patients received during period 1 cetirizine (10 mg po QD) and theophylline (200 mg po BID) for 6 months, followed by period 2 of 1 month washout with only rescue medication as needed, and then by period 3 with cetirizine (10 mg QD plus placebo (BID) for 5 more months. The addition of theophylline resulted in statistically significant improvement over cetirizine alone by 2 months and continued for the duration of treatment. Treatment of cultured human mast cells with theophylline (10 microM) did not inhibit allergic histamine release, but the in vivo beneficial effect of theophylline may require significant pretreatment period to manifest itself, or may involve inhibition of other mast cell dependent mediators. A double-blind study, accompanied by serum histamine and tryptase levels, should be in order.

Corticotropin-releasing hormone induces skin mast cell degranulation and increased vascular permeability, a possible explanation for its proinflammatory effects.

Mast cells are involved in atopic disorders, often exacerbated by stress, and are located perivascularly close to sympathetic and sensory nerve endings. Mast cells are activated by electrical nerve stimulation and millimolar concentrations of neuropeptides, such as substance P (SP). Moreover, acute psychological stress induces CRH-dependent mast cell degranulation. Intradermal administration of rat/human CRH (0.1-10 microM) in the rat induced mast cell degranulation and increased capillary permeability in a dose-dependent fashion. The effect of CRH on Evans blue extravasation was stronger than equimolar concentrations of the mast cell secretagogue compound 48/80 or SP. The free acid analog of CRH, which does not interact with its receptors (CRHR), had no biological activity. Moreover, systemic administration of antalarmin, a nonpeptide CRHR1 antagonist, prevented vascular permeability only by CRH and not by compound 48/80 or SP. CRHR1 was also identified in cultured leukemic human mast cells using RT-PCR. The stimulatory effect of CRH, like that of compound 48/80 on skin vasodilation, could not be elicited in the mast cell deficient W/Wv mice but was present in their +/+ controls, as well as in C57BL/6J mice; histamine could still induce vasodilation in the W/Wv mice. Treatment of rats neonatally with capsaicin had no effect on either Evans blue extravasation or mast cell degranulation, indicating that the effect of exogenous CRH in the skin was not secondary to or dependent on the release of neuropeptides from sensory nerve endings. The effect of CRH on Evans blue extravasation and mast cell degranulation was inhibited by the mast cell stabilizer disodium cromoglycate (cromolyn), but not by the antisecretory molecule somatostatin. To investigate which vasodilatory molecules might be involved in the increase in vascular permeability, the CRH injection site was pretreated with the H1-receptor antagonist diphenhydramine, which largely inhibited the CRH effect, suggesting that histamine was involved in the CRH-induced vasodilation. The possibility that nitric oxide might also be involved was tested using pretreatment with a nitric oxide synthase inhibitor that, however, increased the effect of CRH. These findings indicate that CRH activates skin mast cells at least via a CRHR1-dependent mechanism leading to vasodilation and increased vascular permeability. The present results have implications for the pathophysiology and possible therapy of skin disorders, such as atopic dermatitis, eczema, psoriasis, and urticaria, which are exacerbated or precipitated by stress.

Synergistic action of estradiol and myelin basic protein on mast cell secretion and brain myelin changes resembling early stages of demyelination.

Mast cells are known for their participation in immediate and, more recently, delayed hypersensitivity reactions. They have been found in the meninges and certain brain areas where they are strictly perivascular, in close apposition to neurons, and they are activated by direct nerve stimulation or by neuropeptides. Intracranial mast cells contain many vasoactive substances which can increase the permeability of the blood-brain barrier, proteolytic enzymes which can degrade myelin in vitro, as well as chemotactic molecules which can attract inflammatory molecules in vivo. Connective tissue mast cells, with which intracranial mast cells share many characteristics, contain cytokines which can cause inflammation directly. Multiple sclerosis is a human demyelinating disease of unknown etiology, with a high prevalence in women which results in penetration of blood-borne immune cells within the brain parenchyma and subsequent destruction of myelin. Here, we report that 17 beta-estradiol and myelin basic protein, a major suspected immunogen in multiple sclerosis, had a synergistic action on inducing mast cell secretion. This effect was more pronounced in Lewis rats, which are susceptible to the development of experimental allergic encephalomyelitis, an animal model for multiple sclerosis, than in Sprague-Dawley rats, which are fairly resistant. Moreover, 18 h incubation of purified peritoneal mast cells with homogeneic slices of brain white matter in the presence of 17 beta-estradiol and myelin basic protein resulted in myelin changes resembling early stages of brain demyelination, which were also more evident in Lewis rats than in Sprague-Dawley rats. These results support the notion that mast cells could participate in the pathophysiology of demyelinating diseases.

IL-10 subfamily members: IL-19, IL-20, IL-22, IL-24 and IL-26.

It has been reported that the CD4+ T cell is a very important source of interleukin 10 (IL-10), while CD8+ cells produce low amounts. IL-10 exerts several immune stimulating, as well as inhibitory effects. There are at least five novel human IL-10 family-related molecules: IL-19, IL-20, IL-22, IL-24, and IL-26. Activated T cells produce IL-19, IL-22 and IL-26, while IL-24 is produced by activated monocytes and T-cells. IL-20 induces cheratin proliferation and Stat-3 signal transduction pathway, while IL-22 induces acute-phase production by hepatocytes and neonatal lethality with skin abnormalities reminiscent of psoriasic lesions in humans. In addition, IL-22 mediates inflammation and binds class II cytokine receptor heterodimers IL-22 RA1/CRF2-4. This cytokine is also involved in immuno-regulatory responses. IL-26 (AK155) is a novel cytokine generated by memory cells and is involved in the transformed phenotype of human T cells after infection by herpes virus. All these new IL-10 subfamily member cytokines are strongly involved in immune regulation and inflammatory responses.

Sites of interleukin-6 release in patients with acute coronary syndromes and in patients with congestive heart failure.

This study examines the source of elevated interleukin-6 (IL-6) levels in patients with acute coronary syndrome (ACS) and congestive heart failure (CHF). IL-6 is elevated in the peripheral blood of patients with ACS and CHF, but it is not known if this proinflammatory cytokine is from a cardiac or extracardiac source. Blood samples were obtained from the femoral artery, femoral vein, left main coronary artery, and coronary sinus in 57 patients during cardiac catheterization. IL-6 levels from 12 patients with ACS and 12 patients with CHF were compared with the IL-6 levels in 33 patients who had neither of these clinical conditions. Median IL-6 levels in the peripheral and coronary circulation were a minimum fivefold higher in patients with ACS or CHF relative to control patients. An elevated transcardiac IL-6 gradient (coronary sinus-left main level) was present in patients with ACS (median 5.2; 25th and 75th percentiles 3.9 and 29.3 pg/ml, respectively) compared with control patients (median 0, -0.7 and 0.5 pg/ml; p < 0.001), but not in patients with CHF (median 0.4, -0.7 and 3.5 pg/ml; p = NS). Elevated IL-6 levels in patients with ACS derive from a cardiac source, presumably from "inflamed" coronary plaques and areas of myocardial necrosis, whereas elevated levels in patients with CHF are most likely the result of extracardiac production.

Generation of histamine-releasing activity from serum albumin by medium derived from stimulated neutrophils of rat.

1. Medium conditioned by rat neutrophils stimulated by N-formyl-methionyl-leucyl-phenylalanine (FMLP) has been found to generate mast cell histamine-releasing activity (HRA) when incubated with bovine serum albumin (BSA). 2. Histamine release increased as the concentration of BSA used to generate HRA was increased from 0.25 to 10 mg ml-1, as the concentration of neurotrophil conditioned medium was increased and as the concentration of FMLP used to stimulate the neutrophils was increased. Histamine release was non-cytotoxic as it was inhibited by energy deprivation or by removal of calcium and it was accompanied by degranulation. 3. HRA was detectable after 30 min of incubation with BSA and its generation continued to increase over the 18 h of our measurements. 4. Generation of HRA was dependent upon the presence of medium from stimulated neutrophils and on the presence of BSA, although plasma could substitute for BSA. Likewise, HRA could be generated from gamma-globulin although to a lesser extent than with albumin. 5. Generation was optimum at acid pH and was inhibited by prior boiling of the neutrophil conditioned medium or by the addition of pepstatin. 6. It is suggested that an enzyme(s) released from the neutrophil during stimulation acts on an albumin-like substrate to generate HRA. It is proposed that HRA is peptide in nature and may be generated during an inflammatory response.

Chondroitin sulphate inhibits connective tissue mast cells.

1. Mast cells derive from the bone marrow and are responsible for the development of allergic and possibly inflammatory reactions. Mast cells are stimulated by immunoglobulin E (IgE) and specific antigen, but also by a number of neuropeptides such as neurotensin (NT), somatostatin or substance P (SP), to secrete numerous pro-inflammatory molecules that include histamine, cytokines and proteolytic enzymes. 2. Chondroitin sulphate, a major constituent of connective tissues and of mast cell secretory granules, had a dose-dependent inhibitory effect on rat peritoneal mast cell release of histamine induced by the mast cell secretagogue compound 48/80 (48/80). This inhibition was stronger than that of the clinically available mast cell 'stabilizer' disodium cromoglycate (cromolyn). Inhibition by chondroitin sulphate increased with the length of preincubation and persisted after the drug was washed off, while the effect of cromolyn was limited by rapid tachyphylaxis. 3. Immunologic stimulation of histamine secretion from rat connective tissue mast cells (CTMC) was also inhibited, but this effect was weaker in umbilical cord-derived human mast cells and was absent in rat basophilic leukemia (RBL) cells which are considered homologous to mucosal mast cells (MMC). Oligo- and monosaccharides were not as effective as the polysaccharides. 4. Inhibition, documented by light and electron microscopy, involved a decrease of intracellular calcium ion levels shown by confocal microscopy and image analysis. Autoradiography at the ultrastructural level showed that chondroitin sulphate was mostly associated with plasma and perigranular membranes. 5. Chondroitin sulphate appears to be a potent mast cell inhibitor of allergic and nonimmune stimulation with potential clinical implications.

Inhibition of mast cell secretion by oxidation products of natural polyamines.

Mast cells secrete many biologically active compounds upon stimulation by immunoglobulin E (IgE) and specific antigen (Ag), anaphylatoxins, as well as a number of cationic compounds which include drugs, kinins and neuropeptides. The effects of the two naturally occurring polyamines, spermine (SP) and spermidine (SPD), on mast cell secretion were studied because they have been implicated in the modulation of cellular processes, possibly through their cationic charge or the regulation of calcium ions. SP and SPD over the range of 10(-7) to 10(-4) M inhibited the release of 5-hydroxytryptamine (5-HT, serotonin) triggered by compound 48/80 (C48/80) in a time- and concentration-dependent manner, as long as at least 2% calf serum (CS) was present. SP also inhibited secretion of both histamine and serotonin stimulated immunologically by using IgE and anti-rat IgE. This inhibition was not accompanied by cytotoxicity. The major available polyamine metabolites tested, N1-acetyl spermine (N1-acSP) and N8-acetyl spermidine (N8-acSPD), also showed inhibition in the presence of CS, whereas putrescine, N8,N1-hexamethylene-bis-acetamide (HMBA) and benzylamine did not. Fetal bovine serum (FBS), as well as human and rat serum, which do not contain polyamine oxidase, did not result in any inhibition with the polyamines tested. Inhibitors of the polyamine oxidase blocked the polyamine effect, indicating that the inhibition of mast cell secretion must derive from aldehydes produced from these polyamines. Addition of the aldehyde inhibitor phenylhydrazine (phi-HDZ), simultaneously with, but not following the polyamines, blocked their inhibitory effect, further strengthening the involvement of aldehydes. These results indicate that naturally occurring polyamines may regulate mast cell secretion through metabolic products of polyamine oxidase, a similar enzyme of which is also present in human liver, placenta and pregnant serum.

Quercetin-induced expression of rat mast cell protease II and accumulation of secretory granules in rat basophilic leukemia cells.

Rat basophilic leukemia (RBL) cells are considered to be similar to bone-marrow derived mast cells and to mucosal mast cells (MMC), the latter of which may be involved in inflammatory bowel diseases. RBL cells are not able to accumulate histamine and secretory granules under regular growing conditions. Here we show that the flavonoid quercetin, which inhibits mast cell secretion of histamine, also inhibited RBL cell proliferation and constitutive histamine release while it induced synthesis of rat mast cell protease (RMCP) II and triggered processes leading to accumulation of secretory granules. Cell viability was also retained in the presence of quercetin, whereas untreated cells did not survive past 6 days of growth. Quercetin did not affect the expression of mRNA for alpha-subunit of immunoglobulin E (IgE) receptor, but led to increased expression of mRNA for, and synthesis of RMCP II, which is a marker protein for MMC. Many of these granules showed metachromasia with toluidine blue after 3 days of growth, stained red with alcian blue counterstained with safranin after 8 days of growth, and contained electron dense material. Our results suggest that RBL cells have the capacity to progress to a more mature state and may lend themselves to further analysis of a growth regulator(s) with action similar to that of quercetin.

Rapid degradation of neurotensin by stimulated rat mast cells.

A RIA towards neurotensin (NT) using C-terminal- and N-terminal-specific antisera was used to study degradation of this tridecapeptide by isolated rat mast cells. Incubation of NT (10 microM) with peritoneal or pleural mast cells resulted in a rapid loss of NT immunoreactivity (iNT), as measured by C-terminal-directed antiserum, with little effect on N-terminal iNT. The rate of the reaction was faster with pleural cells (T1/2, 30 s) than with peritoneal cells (T1/2, 180 s) and was greater than 10-fold slower in the presence of metabolic poisons. The enzyme(s) involved is most likely released from the cells during secretion, as NT was degraded by media conditioned by compound 48/80-stimulated mast cells 40-60 times faster than by media from unstimulated cells. This degradation by conditioned media was concentration dependent, pH dependent, and temperature sensitive. HPLC analyses indicated a near stoichiometric conversion of NT to NT(1-12) (66%) and NT(1-11) (34%) after incubation for 10-30 s with conditioned media. By 30 min only NT(1-11) and NT(1-10) were present. Phenanthroline (1 mM), an inhibitor of carboxypeptidase, prevented the loss of C-terminal iNT and the generation of NT(1-12) and NT(1-11). While NT(1-12) was effective in releasing histamine from mast cells in vitro and increasing vascular permeability in vivo, NT(1-11) was not. These results suggest that carboxypeptidase-like enzyme(s) could modulate the level and form of NT-related peptides in various states involving activation of mast cells.

Neurotensin elevates hematocrit and plasma levels of the leukotrienes, LTB4, LTC4, LTD4 and LTE4, in anesthetized rats.

The IV injection of neurotensin (NT) into anesthetized rats produced a marked increase in hematocrit, labored breathing and peripheral blood stasis with cyanosis. This effect could also be produced by the NT-related peptides, neuromedin-N and xenopsin; however, it was not observed when nine other biologically active peptides, including bradykinin and substance P, were tested. Associated with these responses were increases in the plasma levels of histamine (measured radioenzymatically) and the leukotrienes, LTB4, LTC4, LTD4, and LTE4 (measured by RIA and HPLC). The increment in hematocrit after varying doses of NT correlated to the increase in plasma levels of LTC4. Histamine and LTC4 were both capable of elevating hematocrit when given IV; however, LTC4 was approximately 1000 times more potent than histamine and active doses of histamine elevated LTC4 levels. Furthermore, the effects of NT on plasma LTC4 and hematocrit were reduced by pretreating animals with antagonists to histamine and serotonin. Pretreatment with the specific mast cell degranulating agent, compound 48/80, also blocked NT's ability to elevate plasma levels of histamine, LTB4 and LTC4 and prevented the increased hematocrit and cyanosis. These results indicate that NT-related peptides are very potent and specific stimulators of leukotriene release and that this action is mediated by mast cells and associated with loss of plasma volume and blood stasis. A working hypothesis is that histamine, released from mast cells in response to NT, stimulates LTC4 production by other cells.