Somatostatin and macrophage function: modulation of hydrogen peroxide, nitric oxide and tumor necrosis factor release

Somatostatin Derivate (smsDX) Attenuates the TAM-Stimulated Proliferation, Migration and Invasion of Prostate Cancer via NF-κB Regulation

Tumor development and progression are influenced by macrophages of the surrounding microenvironment. To investigate the influences of an inflammatory tumor microenvironment on the growth and metastasis of prostate cancer, the present study used a co-culture model of prostate cancer (PCa) cells with tumor-associated macrophage (TAM)-conditioned medium (MCM). MCM promoted PCa cell (LNCaP, DU145 and PC-3) growth, and a xenograft model in nude mice consistently demonstrated that MCM could promote tumor growth. MCM also stimulated migration and invasion in vitro. Somatostatin derivate (smsDX) significantly attenuated the TAM-stimulated proliferation, migration and invasion of prostate cancer. Immunohistochemistry revealed that NF-κB was over-expressed in PCa and BPH with chronic inflammatory tissue specimens and was positively correlated with macrophage infiltration. Further investigation into the underlying mechanism revealed that NF-κB played an important role in macrophage infiltration. SmsDX inhibited the paracrine loop between TAM and PCa cells and may represent a potential therapeutic agent for PCa.

Octreotide negates the benefit of galantide when used in the treatment of caerulein-induced acute pancreatitis in mice

BACKGROUND

We have previously shown that galantide, a non-specific galanin receptor antagonist, ameliorates acute pancreatitis (AP) induced in mice. Octreotide, a somatostatin analogue, has been used in the treatment of AP with inconsistent outcomes. This study set out to compare the efficacy of a combined treatment of galantide and octreotide with the efficacy of each agent individually in experimental AP.

METHODS

Acute pancreatitis was induced in mice with 7-hourly caerulein injections. Galantide and/or octreotide were co-administered with each caerulein injection commencing with the first injection. Control animals received galantide, octreotide or saline alone. Pancreata were harvested for histological examination and estimation of myeloperoxidase (MPO) activity. Plasma amylase and lipase activities were measured.

RESULTS

Galantide significantly reduced AP-induced hyperenzymaemia by 39-45%. Octreotide alone, or in combination with galantide, did not significantly alter AP-induced hyperenzymaemia. Plasma enzyme activity in the control groups was comparable with pre-treatment activity. Galantide and octreotide administered individually reduced MPO activity by 79% and 50%, respectively; however their combination was without effect. Galantide, octreotide and their combination significantly reduced the percentage of abnormal acinar cells by 28-45%.

CONCLUSIONS

Treatment with galantide alone ameliorated most of the indices of AP studied, whereas treatment with octreotide reduced pancreatic MPO activity and acinar cell damage. Combining the two peptides appears to negate their individual benefits, which suggests an interaction in their mechanism of action.

Differential between protein and mRNA expression of CCR7 and SSTR5 receptors in Crohn's disease patients

Crohn's disease (CD) is a multifactorial chronic inflammatory bowel disease of unknown cause. The aim of the present study was to explore if mRNA over-expression of SSTR5 and CCR7 found in CD patients could be correlated to respective protein expression. When compared to healthy donors, SSTR5 was over-expressed 417 ± 71 times in CD peripheral blood mononuclear cells (PBMCs). Flow cytometry experiments showed no correlation between mRNA and protein expression for SSTR5 in PBMCs. In an attempt to find a reason of such a high mRNA expression, SSTR5 present on CD PBMCs were tested and found as biologically active as on healthy cells. In biopsies of CD intestinal tissue, SSTR5 was not over-expressed but CCR7, unchanged in PBMCs, was over-expressed by 10 ± 3 times in the lamina propria. Confocal microscopy showed a good correlation of CCR7 mRNA and protein expression in CD intestinal biopsies. Our data emphasize flow and image cytometry as impossible to circumvent in complement to molecular biology so to avoid false interpretation on receptor expressions. Once confirmed by further large-scale studies, our preliminary results suggest a role for SSTR5 and CCR7 in CD pathogenesis.

Somatostatin actions via somatostatin receptors on the ocular surface are modulated by inflammatory processes

Recent investigations support the presence of human somatostatin (SS) in the excretory system of the human lacrimal gland. To get deeper insights into a possible role of SS at the ocular surface and in the lacrimal apparatus, we investigated the distribution pattern of SS and its receptors 1-5 (SSTR1-5) by means of RT-PCR, real-time RT-PCR, Western blot and immunodot blot analysis as well as immunohistochemistry in lacrimal gland, tear fluid, conjunctiva, cornea, nasolacrimal duct epithelium, and conjunctival (HCjE) and corneal (HCE) epithelial cell lines. Cell culture experiments with HCjE and HCE were performed to analyze a possible impact of SS and inflammatory mediators on the regulation of SSTR. The results confirmed the presence of SS in lacrimal gland and tear fluid, whereas it was absent at the protein level in all other tissues and cell lines investigated. Expression of SSTR1, -2, and -5 was detectable in lacrimal gland, conjunctiva, cornea, and nasolacrimal ducts. HCjE expressed only hSSTR1 and -2, and HCE revealed only SSTR2. SSTR3 and -4 were not detected in any of the analyzed samples or cell lines. In vitro on cultured immortalized HCjE cells SS leads to a concentration-dependent down-regulation of SSTR1 mRNA but does not affect SSTR2 mRNA expression. Relative expression of SSTR1 and -2 is differentially modulated by proinflammatory cytokines and bacterial components, suggesting that the expression of both receptors is immunomodulated. Our data support an autocrine and paracrine role of SS in the lacrimal system and at the ocular surface and implicate a role of SS in corneal immunology.

Somatostatin receptors and autoimmune-mediated diabetes

Somatostatin (SST) peptide is produced by various SST-secreting cells throughout the body and acts as a neurotransmitter or paracrine/autocrine regulator in response to ions, nutrients, peptides hormones and neurotransmitters. SST is also widely distributed in the periphery to regulate the inflammatory and immune cells in response to hormones, growth factors, cytokines and other secretive molecules. SST peptides are considered the most important physiologic regulator of the islet cell, gastrointestinal cell and immune cell functions, and the importance of SST production levels has been implicated in several diseases including diabetes. The expression of SST receptors has also been found in T lymphocytes and primary immunologic organs. Interaction of SST and its receptors is also involved in T-cell proliferation and thymocyte selection. SSTR gene-ablated mice developed diabetes with morphologic, physiologic and immunologic alterations in the endocrine pancreas. Increased levels of mononuclear cell infiltration of the islets are associated with the increased levels of antigen-presenting cells located in the islets and peripancreatic lymph nodes. Increased levels of SST were also found in antigen-presenting cells and are associated with a significant increase of CD8 expression levels on CD4(+)/CD8(+) immature thymocytes. These findings highlight the crucial role of this neuroendocrine peptide and its receptors in regulating autoimmune functions.

Induction of experimental allergic encephalomyelitis in a low-susceptible Albino Oxford rat strain by somatostatin analogue SMS 201-995

OBJECTIVE

The effect of the somatostatin analogue SMS 201-995 (octreotide; OCT) on the course of experimental allergic encephalomyelitis (EAE) in the relatively resistant Albino Oxford (AO) strain of rats was studied.

METHODS

Animals were actively immunized with bovine brain homogenate in complete Freund's adjuvant. OCT was given subcutaneously in the hind legs on days 7, 8 and 9 after immunization, at a dose of 3 x 5 microg/kg/day. Rats in control groups were treated with saline or were left untreated. EAE was scored clinically and immunophenotypically, estimating by flow cytometry the changes in the popliteal lymph nodes (PLN) and spleen and monitoring immunohistologically the brain sections of rats recovered from disease.

RESULTS

In control AO rats, EAE was induced in only 2 of 22 rats (9%). In OCT-treated rats, however, EAE developed in 11 of 20 rats (55%), in comparison with 3 of 17 saline-treated animals (17%) (p <0.05). In PLN of OCT-treated rats during the clinical course of EAE, a decreased proportion of OX8+ cells was seen, followed by increases in OX39+ and W3/25+ cells on days 17 and 26. In spleen, OCT decreased the proportion of OX1+, OX39+ and OX8+ cells (on days 12 and/or 17), and increased the proportion of OX39+ cells on days 26 and 31. In the brain sections of saline-treated rats recovered from EAE, numerous Mac-1+, Mac-3+ and OX8+ cells were found. These cells were, however, absent in OCT-treated rats; instead, several W3/25+ cells were noticed.

CONCLUSIONS

These data imply that OCT increases the susceptibility of AO rats to EAE, interfering with specific and/or nonspecific defense mechanisms operating in both the initial and recovery phase of EAE.

Somatostatin receptor distribution and function in immune system

Somatostatin and cortistatin, a recently discovered endogenous neuropeptide relative of somatostatin, have multiple modulatory effects on the immune system. The specific somatostatin receptor distribution might in part explain the heterogeneity of effects of somatostatin or its analogs on immunocytes. In fact, somatostatin receptor subtypes are differentially expressed on specific cell subsets within the organs of the immune system and the expression is dynamically regulated and seems to depend on the traffic of these cells through and within lymphoid structure and homing in tissues. Somatostatin effects on immune cells are mainly based on autocrine and paracrine modes of action. In fact, activated cells producing somatostatin (or cortistatin) may interact with other cells expressing the receptors. Here, we review the postulated modes of action of somatostatin and somatostatin-like peptides, including the currently available synthetic somatostatin analogs, in cells of the immune system. We also discuss the wide distribution of somatostatin and its specific five receptor subtypes in immune cell lines, as well as throughout animal and human lymphoid organs, in both normal and pathological conditions.

Somatostatin analogs and radiopeptides in cancer therapy

Since the discovery of somatostatin (sst) in 1973, numerous chemical and biological studies have been carried out to develop sst analogs with enhanced resistance to proteases and prolonged activity. Three highly potent sst analogs-octreotide, lanreotide, and vapreotide-are now available in the clinic, and demonstrate efficacy in the treatment of tumors of the pituitary and the gastroenteropancreatic tract. The most striking effect is the control of hormone hypersecretion associated with these tumors. Available data on growth suppression in patients indicate a limited antiproliferative action, tumor shrinkage is observed in 10-20% patients, and tumor stabilization in about half of the patients for duration of 8-16 months. Eventually, however, all patients escape from sst analog therapy with regard to both hormone hypersecretion and tumor growth, the only exception being observed in acromegalic patients who do not experience tachyphylaxis even after more than 10 years of daily octreotide injection. The mechanism underlying the escape phenomenon is not yet clarified. Regarding the molecular mechanisms involved in sst antineoplastic activity, both indirect and direct effects via specific somatostatin receptors (SSTRs) expressed in the target cells have be described. Direct action may result from blockade of mitogenic growth signal or induction of apoptosis following interaction with SSTRs. Indirect effects may be the result of reduced or inhibited secretion of growth-promoting hormones and growth factors that stimulate the growth of various types of cancer; also, inhibition of angiogenesis or influence on the immune system are important factors. Five SSTR subtypes have been identified so far, which are variably expressed in a variety of tumors such as gastroenteropancreatic (GEP) tumors, pituitary tumors, and carcinoid tumors. Although all five SSTR subtypes are linked to adenylate cyclase, they are now known to affect multiple other cellular signaling systems and hence they differentially participate in the regulation of the various cellular processes. The finding of several laboratories that SSTR-expressing tumors frequently contain two or more SSTR subtypes, and the recent discovery that SSTR subtypes might form homo/heterodimers to create a novel receptor with different functional characteristics, expand the array of selective SSTR activation pathways and subsequent intracellular signaling cascades. This may lead to improved clinical protocols that take into account possible synergistic interactions between the SSTR subtypes present on the same cancer cell. Radiolabeled sst analogs, such as [(111)In]-[diethylenetriamine pentaacetic acid (DTPA)-D-Phe(1)]-octreotide (OcreoScan), have proved to be very useful for tumor scintigraphy and internal radiotherapy of SSTR overexpressing tumors. The recent introduction of the metal chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) considerably improved the stability of the radioconjugates, making possible the incorporation of a variety of radionuclides, such as (90)Y for receptor-mediated radionuclide therapy or (68)Ga for positron emission tomography (PET). Another promising area is the development of sst conjugates incorporating cytotoxic anticancer drugs.

Nitric oxide and octreotide in retinal ischemia-reperfusion injury

This experimental study was performed to investigate the role of ischemia-reperfusion injury on retinal nitric oxide activity and to determine whether octreotide, the synthetic analogue of natural somatostatin, modifies the nitric oxide activity during retinal ischemia-reperfusion in a quinea pig model. Three groups of seven pigmented male quinea pigs were formed; Control, Ischemia and the Ischemia/Octreotide groups. 90 minutes of pressure-induced retinal ischemia and 24 h of reperfusion were established in the ischemia and ischemia/octreotide groups. Saline for the ischemia group and 50 microg/kg of octreotide for the ischemia/octreotide group were administered intraperitoneally five times with 6-h intervals. At the end of the reperfusion period both eyes of the animals of the three groups were enucleated. One eye of each animal was randomly selected for biochemical assay and the other for histopathological analysis. Retinal nitrate levels were measured and histopathological changes were evaluated in the groups. The mean retinal nitrate levels of the control, ischemia and ischemia/octreotide groups were 157.6 +/- 25.2, 106.4 +/- 20.1 and 96.4 +/- 17.7 micromol/l, respectively. Nitrate levels decreased significantly both in the ischemia (p < 0.01) and ischemia/octreotide (p < 0.01) groups versus control. In the ischemia group, retinal histopathological changes, which were different from the control group, were prominent edema, polymorphonucleated leukocytes infiltration and vacuolated spaces in the inner retina. No significant change was observed in the histopathological specimens of the ischemia/octreotide group. Significant increase in the thickness of the inner plexiform layer of the retina of the ischemia group was observed versus the control and ischemia/octreotide groups (p < 0.01 and p < 0.01, respectively). The thickness of the inner plexiform layer of the retina of the ischemia/octreotide group did not change versus the control group. It was concluded that nitric oxide activity decreased during retinal ischemia-reperfusion and, although octreotide prevented the histopathological damage, it could not ameliorate the nitric oxide activity of the retina.

Regulation of apoptosis by somatostatin and substance P in peritoneal macrophages

Recent studies have shown that somatostatin (SOM) inhibits interleukin 6 (IL-6) and interferon gamma (IFNgamma) production by lymphocytes and peritoneal macrophages, whereas substance P (SP) enhances these cytokines production. To define the mechanism of the cytokine production enhancements and inhibitions by SOM and SP, we examined the expression of apoptosis modulator, p53, Bcl-2, Bax, inducible nitric oxide synthase (iNOS), Fas, caspase-8 and nitric oxide (NO) in thioglycolate-elicited peritoneal macrophages. SOM caused up-regulation of p53, Bcl-2, Fas and caspase-8 activities, and down-regulation of iNOS expression and NO production. On the other hand, SP slightly induces p53 and highly induces Bcl-2, iNOS expression and NO production. These data suggest that apoptosis by SOM may occur by a Bax- and NO-independent p53 accumulation, and through Fas and caspase-8 activation pathways, and that the inducible expression of Bcl-2 and NO production by SP may contribute to prevent the signals of apoptosis by Bax, and via Fas and caspase-8 activation.

Bolus somatostatin but not octreotide reduces hepatic sinusoidal pressure by a NO-independent mechanism in chronic liver disease

BACKGROUND

Evidence exists that somatostatin and octreotide might have different effects on hepatic haemodynamics.

AIM

The investigation of the effects of somatostatin and its octapeptide analogue, octreotide, on sinusoidal pressure measured by the wedged hepatic venous pressure in patients with cirrhosis or chronic hepatitis and the correlation with the levels of hepatic vein NO.

METHODS

Patients were randomly assigned to receive an injection of either 250 microg somatostatin (n=14: cirrhosis six, chronic hepatitis eight) or an injection of 125 microg octreotide (n=19: cirrhosis nine, chronic hepatitis 10) during hepatic vein catheterization. Baseline wedged hepatic venous pressure was measured, followed by measurements at 2, 5, 10 and 15 min after the injection of the drug. Nitrites/nitrates of the hepatic vein were measured before the injection and after 15 min.

RESULTS

Both agents showed a similar qualitative but a different quantitative haemodynamic profile. No change in the wedged hepatic venous pressure was observed during the first 2 min after the injection of both drugs. This was followed by a decrease: 18% at 5 min (N.S.), 23% at 10 min (P < 0.01) and 24% at 15 min (P < 0.01) for somatostatin. Octreotide induced a relatively smaller decrease in the wedged hepatic venous pressure: 8% at 5 min (N.S.), 20% at 10 min (P < 0.01) and 16% at 15 min (N.S.). Further analysis of the sub-groups of cirrhotic and chronic hepatitis patients revealed a different effect. In the sub-group of cirrhotic patients, somatostatin caused a maximum decrease of 34% at 15 min post-injection (P < 0.01), but octreotide failed to produce a significant change on the wedged hepatic venous pressure. In contrast, no change was observed in chronic hepatitis patients with either drug. No change in the hepatic vein concentration of NO after treatment was observed with either somatostatin or octreotide. Moreover, no correlation of the levels of NO with the wedged hepatic venous pressure values was found.

CONCLUSIONS

This study shows that somatostatin is more effective than octreotide in acutely reducing the wedged hepatic venous pressure after bolus injection and the observed change is probably mediated by a NO-independent mechanism.

Peptides as regulators of the immune system: emphasis on somatostatin

Study of the communication between nervous and immune systems culminated in the understanding that cytokines, formerly considered exclusively as immune system-derived peptides, are endogenous to the brain and display central actions. More recently, immune cells have been recognized as a peripheral source of "brain-specific" peptides with immunomodulatory actions. This article reviews studies concerning reciprocal effects of selected cytokines and neuropeptides in the nervous and immune systems, respectively. The functional equivalence of these two categories of communicators is discussed with reference to the example of the actions of neuropeptide somatostatin in the immune system.

Selenium stimulates estradiol production in bovine granulosa cells: possible involvement of nitric oxide

Reduction in fertility is well known to be possibly related to selenium deficiencies, even if target organ for selenium action is, at present, unclear. The present study was aimed to examine whether selenium directly influences granulosa cells. Bovine granulosa cells from different size follicles were used to investigate the effect of selenium (5 ng/ml), with or without bovine follicle-stimulating hormone (bFSH) (100 ng/ml), on proliferation and steroidogenesis. In addition, we sought to determine if selenium modulates the production of nitric oxide, which is known to play an important role in ovarian activity. Our data demonstrate that selenium significantly (P < 0.001) stimulates the proliferation of the cells from small follicles; moreover, it further potentiates the stimulatory effect of the gonadotropin in the same cells. Furthermore, selenium significantly (P < 0.01) augments E2 output by cells from both kinds of follicles. bFSH increases E2 production (P < 0.01) by cells from large follicles, whereas it exerts a stimulatory (P < 0.01) effect only in the presence of selenium in the cells from the small ones. The production of nitric oxide is significantly increased (P < 0.001) by bFSH, but only in cells from small follicles. Selenium inhibits (P < 0.001) nitric oxide production in cells from both kinds of follicles and significantly decreases (P < 0.001) bFSH-induced nitric oxide production in cells from the small ones. We conclude that selenium acts on granulosa cells by modulating their proliferation and E2 synthesis; moreover, its effect could be mediated, at least in part, through an inhibition of nitric oxide.

Effects of octreotide treatment on early TNF-alpha production and localization in experimental chronic colitis

BACKGROUND

Colitis induced by trinitrobenzene sulphonic acid (TNB) is a model of Th1 disease, mainly explored from the third day of induction. It has recently been shown that octreotide and other somatostatin analogues can modify inflammatory/immune processes by acting on cytokines.

AIM

To examine TNFalpha production and the effect of preventive treatment with octreotide, during the early phase of TNB-colitis.

METHODS

Thirty milligrams TNB with 50% ethanol was instilled into the colon of male Wistar rats. Treated groups received octreotide (2x10 microg x day/rat) or dexamethasone (1x2 mg x day/kg), subcutaneously, with the first injection before TNB. Eight and 80 h later, the colon was excised and processed for histology, TNFalpha immunohistochemistry, quantification of cytokine release ex vivo and tissue-inducible NO synthase (iNOS) activity.

RESULTS

Maximal TNFalpha production was observed at the 8th hour, associated with intense immunostaining of the external muscle layer. Octreotide treatment decreased TNFalpha expression (staining and activity) and iNOS activity. At the 80th hour, submucosal macrophages were positive for TNFalpha and colonic production of IL1beta and interferon gamma was increased; all these effects were reduced by octreotide treatment.

CONCLUSIONS

TNFalpha was expressed early by resident muscle cells, before staining of infiltrated immune cells and increased production of interferon gamma. TNFalpha regulation by octreotide suggests that this drug might exert anti-inflammatory properties via smooth muscle cells.

Somatostatin and octreotide modulate the function of Kupffer cells in liver cirrhosis

In our previous studies we have shown that somatostatin and octreotide modulate the function of peritoneal macrophages and Kupffer cells in noncirrhotic livers. However, the effects of somatostatin on the Kupffer cells in cirrhotic livers are not known. In the present study, Kupffer cells, obtained from male rats with carbon tetrachloride-induced cirrhotic livers, were treated in vitro with somatostatin or octreotide and their effects on the release of nitric oxide, tumor necrosis factor-alpha (TNF-alpha) and peroxide (H2O2) determined. At concentrations of 10(-13) or 10(-10) to 10(-6) M of somatostatin or 10(-12) to 10(-10) M, or 10(-6) M of octreotide, the amount of nitric oxide released by Kupffer cells was significantly suppressed relative to that of untreated cells. Kupffer cells treated with less than 10(-12) M or greater than 10(-12) M of somatostatin or octreotide released less TNF-alpha compared to the untreated controls. In addition, zymosan-induced H2O2 release by Kupffer cells treated with 10(-9) to 10(-7) M somatostatin or with 10(-15) to 10(-13) M and 10(-9) to 10(-7) M of octreotide was greater than that of the untreated controls. These findings demonstrate that somatostatin and octreotide modulate the release of nitric oxide, TNF-alpha and H2O2 by Kupffer cells in cirrhotic livers depending on the concentrations of hormones used.

Growth hormone. A paracrine growth factor?

A number of tissues, including the brain, pituitary, immune system, placenta, mammary gland, and testis, may be self-contained units of GH regulation, production, and action. The production of GH and GH-releasing factors outside the hypothalamo-pituitary axis complements, rather than replaces, the traditional endocrine interactions between GH-releasing factors, GH, and its target tissues.

Inhibition of gamma interferon synthesis by catecholamines

In vitro incubation of Listeria monocytogenes immune spleen cells in the presence of the catecholamines epinephrine or norepinephrine inhibited the gamma interferon (IFN-gamma) synthesis induced by the mitogen PHA, in a manner that appeared to be concentration dependent. Moreover, the inhibitory effect of both catecholamines epinephrine and norepinephrine on the synthesis of IFN-gamma was prevented by incubating immune spleen cells in the presence of propranolol, a beta adrenergic antagonist agent.

Somatostatin modulates the function of Kupffer cells

Recent studies have shown that somatostatin modulates lymphocyte and peritoneal macrophage function, but the effects of somatostatin on hepatic macrophages (Kupffer cells) are not clearly defined. In the present study, hepatic macrophages obtained from male rats were treated in vitro with somatostatin or octreotide and their effects on the release of nitrite, tumor necrosis factor (TNF), and hydrogen peroxide (H2O2) determined. At concentrations of 10(-14) M to 10(-12) M, or greater than 10(-10) M, somatostatin suppressed nitrite release by Kupffer cells. At concentrations of less than 10(-9) M or greater than 10(-9) M, octreotide inhibited nitrite release by Kupffer cells. Kupffer cells treated with 10(-10) M to 10(-14) M or greater than 10(-8) M of somatostatin released significantly less amounts of TNF than did the untreated controls. TNF release by Kupffer cells treated with 10(-15) M to 10(-5) M of octreotide was significantly inhibited as compared to that of untreated controls. Kupffer cells treated with 10(-14) M to 10(-11) M and 10(-9) M to 10(-8) M of somatostatin released more H2O2 than did the untreated controls. The amount of H2O2 released by noncirrhotic Kupffer cells treated with 10(-6) M or 10(-5) M of somatostatin was less than that of controls. These findings demonstrate that somatostatin and octreotide modulate the release of nitric oxide, TNF, H2O be Kupffer cells depending on the concentration of hormones used.

Effects of atrial natriuretic peptide on phagocytosis and respiratory burst in murine macrophages

Atrial natriuretic peptide (ANP) is known to affect cardiovascular physiology displaying both hormone- and neurotransmitter characteristics. However, there is increasing evidence that ANP possesses additional biological activities referring to the immune system. To further strengthen this hypothesis the effect of ANP on two major functions of macrophages, i.e., phagocytosis and respiratory burst was tested. Both parameters were analyzed by flow cytometry employing bone marrow derived macrophages and the murine macrophage cell line J774. In both cell types preincubation with ANP dose dependently (10(-10)-10(-7) M) increases ingestion of opsonized fluorescent latex particles. The respiratory burst activity was monitored by oxidation of dihydrorhodamine-123 in cells stimulated either with phorbol-myristate (PMA, 10 ng/ml) or formyl-Met-Leu-Phe (fMLP, 1 microM). In both cases preexposure of cells to ANP (10(-8)-10(-6) M) for 2 h enhances reactive oxygen production. The data demonstrate an influence of ANP on important defense mechanisms of macrophages and thus extend the knowledge regarding the pharmacological profile of this natriuretic peptide.

Catecholamines inhibit alpha/beta interferon production induced by lipopolysaccharide

In vitro incubation of Listeria monocytogenes immune spleen cells in the presence of the catecholamines epinephrine or norepinephrine inhibited the alpha/beta-interferon (IFN alpha/beta) synthesis induced by the mitogen lipopolysaccharide, in a manner that appeared to be concentration-dependent. Moreover, the inhibitory effect of both catecholamines epinephrine and norepinephrine on the synthesis of IFN alpha/beta was prevented by incubating immune spleen cells in the presence of propranolol, a beta-adrenergic antagonist agent.