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P Navarra

Publications and source records attributed to P Navarra.

At least 55 records · Page 3Linked to original sources
PubMed1997

The release of immunoreactive interleukin-1 beta from rat hypothalamic explants is modulated by neurotransmitters and corticotropin-releasing hormone.

Both constitutive and inducible interleukin-1 (IL-1) gene expressions have been described in the central nervous system, the former being associated with immunoreactive IL-1 neurons in human and rat hypothalami. While most studies have focused on the role of IL-1 as a mediator of pathological events in the brain, the cytokine of neuronal origin might also be involved in the regulation of physiological processes. In this study we used a previously validated technique to investigate the effects of classical neurotransmitters and the hypophysiotropic peptide corticotropin-releasing hormone (CRH) on the release of immunoreactive (ir) IL-1 beta from acute rat hypothalamic explants. We found that basal irIL-1 beta secretion is significantly inhibited by acetylcholine and histamine and increased by dopamine, while dexamethasone, IL-4 and IL-10 have no effect. Moreover, cytokine release is dose-dependently increased by CRH. Such effects of the neurotransmitters and CRH are observed in short-term incubation experiments, indicating that a pre-formed pool of hypothalamic IL-1 beta is involved. These findings also suggest that the interaction between IL-1, neurotransmitters and neuropeptides might play a role in the physiological regulation of such processes as body temperature, food intake and the control of hypothalamic-hypophyseal axes.

Acetylcholine↗
PubMed1997

Evidence that carbon monoxide stimulates prostaglandin endoperoxide synthase activity in rat hypothalamic explants and in primary cultures of rat hypothalamic astrocytes.

Carbon monoxide (CO) shares with nitric oxide (NO) the ability to modulate the release of hypophysiotropic peptides from rat hypothalamic explants. While both gases are believed to act as neural messengers in the brain via the activation of soluble guanylyl cyclase, the latter is almost undetectable in the rat hypothalamus. NO has been shown to exert some of its biological actions through the modulation of prostaglandin endoperoxide synthase (PGHS) activity. We have, therefore, investigated whether CO also can use PGHS as a signaling pathway in the hypothalamus. Endogenous CO is produced in equimolar amounts with biliverdin (BV) by the catabolism of hemin through heme oxygenase (HO). Hemin, two inhibitors of HO, zinc-protoporphyrin-9 (ZnPP9) and tin-mesoporphyrin-9 (SnMP9), ferrous hemoglobin (Hb), indomethacin and dexamethasone (DEX) were used as pharmacological tools. Prostaglandin E2 (PGE2) released from rat hypothalamic explants or primary cultures of hypothalamic astrocytes was taken as a marker of PGHS activity. It was found that: (1) hemin evokes an increase in PGE2 release from hypothalamic explants; (2) this effect is counteracted by ZnPP9, SnMP9, Hb and indomethacin; (3) the metallo-porphyrins and indomethacin, but not Hb, are also able to inhibit basal PGE2 release from hypothalamic explants; and (4) dexamethasone does not inhibit, and even potentiates, the stimulatory effect of hemin on PGE2 release from hypothalamic astrocytes. The evidence presented here suggests that the catabolism of endogenous or exogenously added hemin is associated with an increase in PGE2 production in the rat hypothalamus. This effect can be attributed to the formation of CO, since the other end-product of HO, BV, does not enhance PGE2 release. Thus, at least some of the biological effects of CO at the hypothalamic level might be mediated by the activation of the PGHS pathway.

Animals↗
PubMed1997

Hydroxyurea induces the gene expression and synthesis of proinflammatory cytokines in vivo.

The anticancer agent hydroxyurea (HU) was previously found to cause dose-dependent adrenal activation in the rat. The increased secretion of corticosterone (CORT) that results appeared to protect animals against HU toxicity, which was dramatically enhanced in adrenalectomized (ADX) rats. Similarities with the endocrine and toxicological profiles of proinflammatory cytokines such as interleukin (IL)-1 and tumor necrosis factor (TNF) led us to suggest that these effects of HU might be mediated by an increased synthesis of these cytokines. The goal of this study was therefore to demonstrate that HU induces the gene expression and synthesis of proinflammatory cytokines in vivo. Intact and ADX rats were treated with HU, mRNA was extracted from spleen cells 2 and 24 hr after treatment and message levels for IL-1 alpha, IL-2, IL-4, IL-6, TNF alpha and interferon-gamma were evaluated using the reverse transcriptase-polymerase chain reaction technique. In some experiments, circulating levels of CORT and TNF were also measured. We found that transcripts of the proinflammatory cytokines, TNF, IL-6 and (though less clearly) IL-1 alpha, were expressed in the majority of intact rats treated with HU but were absent or less evident in most controls. In contrast, gene expression of IL-2, IL-4 and interferon-gamma was not influenced by drug treatment. Adrenalectomy markedly enhanced the effects of HU. Twenty-four hours after administration of the drug, the expression of TNF and IL-6 mRNAs was still higher in ADX rats compared with intact animals. Parallel measurements of plasma CORT levels revealed that gene expression of IL-1 alpha and, to a lesser extent, TNF was inversely related to levels of circulating CORT. Adrenalectomy per se caused a significant increase in plasma TNF levels compared with intact controls. Hydroxyurea elicited significant increases in circulating TNF in both ADX and intact rats. These findings lend support to our working hypothesis and provide an explanation for both the rise in glucocorticoid secretion induced by HU in intact rats and the increase in lethality observed in animals with disruptions of the hypothalamo-pituitary-adrenal axis.

Adrenalectomy↗
PubMed1996

Evidence for the neuronal origin of immunoreactive interleukin-1 beta released by rat hypothalamic explants.

In this study, we have investigated the release of immunoreactive interleukin-1 beta (irIL-1 beta) from the rat hypothalamus in vitro. It was found that (1) tissue explants release sizable amounts of irIL-1 beta (ranging from 0.43 to 0.52 pg/mg of wet tissue) in 20 min incubations; (2) basal release in significantly increased by depolarization induced with 56 mM KCl; (3) K(+)-induced irIL-1 beta release is inhibited by the specific blocker of N-type calcium channels, omega-conotoxin, and by verapamil, but not by nifedipine; (4) K(+)-induced release is also inhibited by the Na+ channel blockers tetrodotoxin and lidocaine; (5) irIL-1 beta release is significantly increased by noradrenalin; such increase is antagonized by verapamil and the beta-blocker propranolol, but not by the alpha-blocker phentolamine. The present evidence suggests that irIL-1 beta released by rat hypothalamic explants following KCl depolarization is neuronal in origin.

Animals↗
PubMed1996

Synthetic alleles at position 121 define a functional domain of human interleukin-1 beta.

The non-conservative substitution of the tyrosine residue at position 121 of human interleukin-1 beta (IL-1 beta) generates protein mutants showing strong reduction of the capacity to induce (a) prostaglandin E2 (PGE2) release from fibroblasts and smooth muscle cells, (b) murine T-cells proliferation and (c) activation of interleukin-6 (IL-6) gene expression. It is generally accepted that these functions are mediated by the type-I interleukin-1 receptor (IL-1RI). However, the mutant proteins maintain the binding affinity to the types-I and II IL-1 receptors, which is the same as the control IL-1 beta, suggesting that this amino acid substitution does not alter the structure of the molecule, except locally. Thus we have identified a new functional site of IL-1 beta different from the known receptor binding region, responsible for fundamental IL-1 beta functions. Moreover, we show that the same mutants maintain at least two hypothalamic functions, that is, the in vitro short-term PGE2 release from rat hypothalamus and the induction of fever in rabbits. This result suggests that there is yet another site of the molecule responsible for the hypothalamic functions, implying that multiple active sites on the IL-1 beta molecule, possibly binding to more than one receptor chain, trigger different signals.

Alleles↗
PubMed1996

The effects of inhibitors of cyclo-oxygenase, lipoxygenase and nitric oxide synthase pathways on the toxicity of hydroxyurea in adrenalectomized rats.

Our previous observations on the toxic effects of hydroxyurea (HU) in adrenalectomized (ADX) rats prompted us to suggest that these effects might be mediated by an increased synthesis of proinflammatory cytokines, which display similar toxicological profiles (e.g. increased lethality in adrenal-ablated animals). The present study was aimed at investigating whether some of the mediators of the biological effects of pro-inflammatory cytokines (i.e. prostaglandins, leukotrienes, and nitric oxide) are involved in the severe HU toxicity seen in ADX rats. The latter were treated over a 5-day period with HU alone or HU plus specific inhibitors of prostaglandin, leukotriene and nitric oxide synthetic pathways. Mortality was recorded throughout the experiments. Results showed that, while corticosterone and dexamethasone afford significant protection against HU toxicity, the latter is not reduced and may even be aggravated by treatments with specific inhibitors of cyclo-oxygenase, lipoxygenase or nitric oxide synthase.

Adrenalectomy↗
PubMed1996

Increased production and release of prostaglandin-E2 by human granulosa cells from polycystic ovaries.

This study was conducted to compare the levels of prostaglandin E2 (PGE2) released by cultured granulosa cells collected from normally-ovulating women (normal cells, NC) and those with polycystic ovaries (polycystic ovary granulosa cells, POGC). Granulosa cells were collected from 7 normal women and 7 anovulatory women with polycystic ovaries. Both groups underwent laparoscopic oocyte retrieval for gamete intra-fallopian transfer. Cell cultures were carried out under basal conditions and in the presence of various substances known to influence PGE2 biosynthesis. Prostaglandin E2 concentrations in the incubation media were taken as a marker of cyclo-oxygenase activity. Unexpectedly, POGC appeared to release greater amounts of PGE2 compared to the NC. There was no difference between the levels of PGE2 produced by the two types of cells during the first 3 hours after cell explants, whereas a difference (P < 0.01) was observed after 24 and 48 hours of incubation. Interleukin-1 beta enhanced PGE2 secretion (P < 0.01) in both POGC and NC, while lipopolysaccharide increased prostaglandin release only by the NC cells. Indomethacin inhibited PGE2 production to a greater extent in POGC (from -70 to -90% with respect to basal release, P < 0.01) than NC (approximately -50%, P < 0.01). Blockade by indomethacin and the weak inhibitory effect of the glucocorticoid, dexamethasone (P < 0.05 only in NC, and only at 24 hours), provided pharmacological evidence that PG production by granulosa cells in vitro might depend primarily on constitutive cyclo-oxygenase activity.

Administration, Topical↗
PubMed1996

Oxytocin release is inhibited by the generation of carbon monoxide from the rat hypothalamus--further evidence for carbon monoxide as a neuromodulator.

Recent evidence suggests that the gas nitric oxide can modulate the secretion of a number of hypothalamic hormones, and may be co-localized particularly to oxytocin-containing neurons. Another gas, carbon monoxide (CO), has also been suggested to play a role in neural signaling in the brain, and the synthetic enzyme responsible for the generation of carbon monoxide has been reported to be present in the rat hypothalamus. In this study, we have therefore investigated whether CO has the ability to modify the release of oxytocin from acute rat hypothalamic explants. Hemin, a specific CO precursor through the enzyme heme oxygenase (the enzymatic pathway synthesizing endogenous CO, was found to inhibit KCl-stimulated oxytocin release, with a maximal effect at 10(-5) M, while showing no effect on basal oxytocin secretion. The stimulation of oxytocin by serotonin 10 ng/ml was also significantly antagonized by hemin 10(-7) M. An inhibitor of heme oxygenase, zinc-protoporphyrin-9, had no effect on basal or stimulated oxytocin release. When hemin and zinc-protoporphyrin-9 were given together, the hemin-induced inhibition of oxytocin was completely antagonized by the enzyme inhibitor. Ferrous hemoglobin A0, a substance known to bind CO with high affinity, had no effect on either basal or stimulated oxytocin release, but when hemin and ferrous hemoglobin A0 were given together the hemin-induced inhibition of oxytocin was completely blocked. These findings provide evidence that endogenous CO may play a role in the control of oxytocin release and that, by analogy with nitric oxide, CO may represent a major new neuroendocrine modulator.

Animals↗
PubMed1996

Interleukin-1 beta release from rat gastric fundus.

Interleukin-1 (IL-1) is known to regulate gastric functions via a central action at the hypothalamic level, and it has also been shown that this cytokine can directly modulate rat gastric motility. This study was conducted to determine whether IL-1 beta is produced and released by rat gastric fundi in vitro. IL-1 beta immunoreactivity was released in measurable amounts from explanted rat gastric tissue. This release was not affected by electrical stimulation of the gastric strips or by agents that induce IL-1 biosynthesis. It could be inhibited only by the glucocorticoid dexamethasone. Ex vivo experiments confirmed the inhibitory role of glucocorticoids and showed that IL-1 beta release can be inhibited by agents that reduce gastric acid secretion, suggesting that the latter might stimulate IL-1 beta synthesis and release. In light of the well-established gastroprotection exerted by IL-1, H(+)-induced IL-1 beta release might serve as a protection against mucosal injuries caused by acid secretion, and the inhibition of this release by glucocorticoids might be involved in the pathogenesis of gastric damage associated with severe stress or steroid therapy.

Adrenalectomy↗
PubMed1995

Interleukin-1 receptor antagonist displays intrinsic agonist activity on rat gastric fundus motility in vitro.

It has been shown previously that both forms of interleukin-1, 1 alpha and 1 beta, produce dose-dependent relaxation of the rat gastric fundus in vitro, accompanied by an increased production and release of eicosanoids. This effect appears to be mediated, at least in part, by leukotrienes, since the inhibition of 5-lipoxygenase by specific drugs counteracts interleukin-1-induced gastric relaxation. In the present study, we attempted to antagonize interleukin-1-induced inhibition of gastric fundus motility with a interleukin-1 receptor antagonist. Surprisingly, the interleukin-1 receptor antagonist itself possessed interleukin-1-like agonist activity, since: (a) it produced rapid, dose-dependent relaxation of the rat gastric fundus, with an estimated EC50 of 70 pg/ml and a maximal effect at 10 ng/ml; (b) interleukin-1 receptor antagonist-induced relaxation was dose dependently inhibited by N-(3-phenoxycinnamyl)acetohydroxamic acid (BW A4c), a specific inhibitor of 5-lipoxygenase; (c) in the first 5 min after its addition to the bath solution, interleukin-1 receptor antagonist produced a significant increase in prostaglandin E2 release from the gastric strips. This evidence suggests that, shortly after receptor occupancy, in this experimental model interleukin-1 and interleukin-1 receptor antagonist share the same pattern of mechanical and biochemical activities.

Analysis of Variance↗
PubMed1995

Evidence that the interleukin-1 beta-induced prostaglandin E2 release from rat hypothalamus is mediated by type I and type II interleukin-1 receptors.

Interleukin-1 beta (IL-1 beta) has been shown to specifically increase the release of prostaglandin (PG) E2 from rat hypothalamic explants in short-term experiments. In this study we attempted to characterize the receptor subtype(s) involved in this response. Rat hypothalamic explants were incubated with mouse monoclonal antibodies (mAbs) raised against human IL-1 type I or type II receptors, IL-1 receptor antagonist (IL-1ra) and alpha-melanocyte-stimulating hormone (alpha-MSH) (which appears to antagonize certain IL-1 induced inflammatory effects in vivo), alone and in the presence of IL-1 beta. PGE2 released into the incubation medium was measured by radioimmunoassay. The anti-type I mAb reduced both basal and IL-1 beta-stimulated PGE2 release at 10 micrograms/ml, but not at lower concentrations. The anti-type II mAb also produced a significant decrease in stimulated release but had no effect on basal release. IL-1ra mimicked the effects of the anti-type I mAb, while alpha-MSH failed to alter either basal or stimulated PGE2 release. These findings suggest that IL-1 beta controls production and release of PGE2 by the rat hypothalamus via both type I and type II receptors, although the latter appear to be involved only in the response to high levels of IL-1.

Animals↗
PubMed1995

Anticancer drug toxicity via cytokine production: the hydroxyurea paradigm.

Our previous observations on the toxic effects of hydroxyurea (HU) in adrenalectomized (ADX) rats prompted us to suggest that these effects might be mediated by an increased synthesis of proinflammatory cytokines. This study was conducted to determine whether HU stimulates cytokine gene expression in vivo. The polymerase chain reaction (PCR) technique was used to assess levels of mRNA for interleukin-1 alpha (IL-1 alpha), tumor necrosis factor (TNF) and interleukin-4 (IL-4) in spleen cells from intact and ADX rats treated with HU or vehicle. In ADX rats, expression of proinflammatory-cytokine mRNA was markedly increased by HU, but no expression of these genes was seen in intact animals after treatment. In the latter rats, cytokine-gene expression seemed to be down-regulated by HU-induced elevations in plasma corticosterone levels, since IL-1 alpha and TNF transcripts could be detected only after corticosterone levels had returned to normal (24 h after treatment). Interestingly, IL-4 mRNA could not be detected in either treated or untreated ADX rats, indicating that expression of this gene is closely related to circulating levels of corticosterone. These findings strongly suggest that the increased toxicity displayed by HU in ADX animals is mediated by stimulation of cytokine synthesis in vivo.

Adrenalectomy↗
PubMed1994

Evidence that interleukin-1 beta and tumor necrosis factor inhibit gastric fundus motility via the 5-lipoxygenase pathway.

In this study, we compared the effects of interleukin-1 beta and tumor necrosis factor (TNF) on in vitro rat gastric fundus motility. Interleukin-1 beta produced rapid, concentration-dependent relaxation of rat gastric fundus strips, similar to that seen with TNF, with a maximal effect at 30 U/ml and an estimated EC50 at 0.9 U/ml. The relaxant effects of interleukin-1 beta and TNF were not influenced by the inhibition of cyclooxygenase or nitric oxide-synthase activities. Interleukin-1 beta- and TNF-induced gastric relaxations were concentration dependently inhibited by BW 755c, which inhibits both cyclooxygenase and lipoxygenase, BW A4, which selectively inhibits the 5-lipoxygenase pathway, and SC 41930, a selective leukotriene B4 receptor antagonist, providing pharmacological evidence that leukotriene B4 is involved in the relaxant effects of both cytokines. The interleukin-1 beta- and TNF-induced activation of 5-lipoxygenase pathway did not appear to be triggered by phospholipase A2. An alternative pathway could involve the following steps: (i) activation of phospholipase C and the formation of diacylglycerol; (ii) diacylglycerol-induced activation of protein kinase C; (iii) formation of free arachidonic acid from diacylglycerol by diacylglycerol-lipase. This mechanism is suggested by the finding that leukotriene B4 is able to mimic cytokine-induced strip relaxation only in the presence of phorbol 12-myristate 13-acetate, which selectively activates protein kinase C.

Animals↗
PubMed1994

Regulation of interleukin 6 production by cAMP-protein kinase-A pathway in rat cortical astrocytes.

In this study we analysed the involvement of the cAMP-protein kinase-A system in the regulation of interleukin 6 production by cultured cortical astrocytes. Vasoactive intestinal peptide strongly increased, in a dose-dependent manner, interleukin 6 production. This effect was reduced when protein kinase A was blocked by KT-5720; it was not affected by calphostin C, a protein kinase C inhibitor. Forskolin caused a concentration-dependent increase in interleukin 6 release, that was also inhibited by KT-5720. Since prostaglandins are believed to play a role in interleukin 6 production, we tried to determine whether the stimulatory effects of vasoactive intestinal peptide and forskolin on cytokine release might be mediated by stimulation of prostaglandin production in cortical astrocytes. Vasoactive intestinal peptide did not increase the production of either prostaglandin E2 or F2 alpha. Conversely, forskolin concentration-dependently stimulated the production of both prostaglandins, an effect that was blocked by indomethacin. Indomethacin did not affect either vasoactive intestinal peptide- or forskolin-stimulated interleukin 6 production. To exclude the possibility that prostaglandins participate in interleukin 6 production induced by forskolin, we tested the effect of prostaglandins E2 and F2 alpha on the cytokine production. The former was completely ineffective in eliciting the cytokine production, while prostaglandin F2 alpha slightly increase interleukin 6 only at the highest concentration. 8-Br-cAMP and (BU)2- cAMP stimulated interleukin 6 production to a lesser extent than vasoactive intestinal peptide and forskolin. In conclusion, we provide evidence that vasoactive intestinal peptide increases interleukin 6 production by astrocytes through the stimulation of the cAMP-protein kinase-A pathway, an effect that is reproduced by cAMP analogues. In addition, we point out that prostaglandins are not involved in vasoactive intestinal peptide- and forskolin-mediated induction of interleukin 6 production in cultured astrocytes.

Animals↗
PubMed1994

Interleukin-1 beta- and tumour-necrosis-factor-induced inhibition of rat gastric fundus motility in vitro.

In this study, we compared the effects of interleukin-1 beta (IL-1 beta) and tumour necrosis factor (TNF) on in vitro rat gastric fundus motility. IL-1 beta and TNF produced rapid, concentration-dependent relaxation of the rat gastric fundus strips with maximal effect at 300 pg ml-1 and 10 ng ml-1, and estimated EC50S at 10 and 450 pg ml-1, respectively. The relaxant effects of IL-1 beta and TNF were not influenced by the inhibition of cyclo-oxygenase or NO-synthase activities. IL-1 beta- and TNF-induced gastric relaxations were inhibited by BW 755c, which inhibits both cyclo-oxygenase and lipoxygenase (LO), BW A4c, which selectively inhibits the 5-LO pathway, and SC 41930, a selective leukotriene B4 (LTB4) receptor antagonist, providing pharmacological evidence that LTB4 is involved in the relaxant effects of both cytokines. The IL-1 beta- and TNF-induced activation of 5-LO pathway did not appear to be triggered by phospholipase A2. An alternative pathway could involve the activation of a phospholipase C, specific for phosphatidylcholine, from which, in sequence: the formation of diacylglycerol (DAG), DAG-induced activation of protein kinase C and the formation of free arachidonic acid from DAG would ensue. This mechanism is suggested by the finding that LTB4 is able to mimic cytokine-induced strip relaxation only in the presence of phorbol 12-myristate 13-acetate, which selectively activates protein kinase C.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1994

Vasoactive intestinal peptide and forskolin stimulate interleukin 6 production by rat cortical astrocytes in culture via a cyclic AMP-dependent, prostaglandin-independent mechanism.

In this study we analyzed the involvement of the cyclic AMP (cAMP)-protein kinase A system in the regulation of interleukin 6 production by cultured cortical astrocytes. Vasoactive intestinal peptide strongly increased, in a dose-dependent manner, interleukin 6 production. This effect was reduced when protein kinase A was blocked by KT-5720; it was not affected by calphostin C, a protein kinase C inhibitor. Forskolin caused a concentration-dependent increase in interleukin 6 release that was also inhibited by KT-5720. Because prostaglandins are believed to play a role in interleukin 6 production, we tried to determine whether the stimulatory effects of vasoactive intestinal peptide and forskolin on cytokine release might be mediated by stimulation of prostaglandin production in cortical astrocytes. Vasoactive intestinal peptide did not increase the production of either prostaglandin E2 or F2 alpha. Conversely, forskolin concentration-dependently stimulated the production of both prostaglandins, an effect that was blocked by indomethacin. Indomethacin did not affect either vasoactive intestinal peptide- or forskolin-stimulated interleukin 6 production. To exclude the possibility that prostaglandins participate in interleukin 6 production induced by forskolin, we tested prostaglandins E2 and F2 alpha. The former was completely ineffective in eliciting the cytokine production, whereas prostaglandin F2 alpha slightly increased interleukin 6 production only at the highest concentrations. 8-Bromo-cAMP and dibutyryl-cAMP stimulated interleukin 6 production to a lesser extent than vasoactive intestinal peptide and forskolin. In conclusion, we provide evidence that vasoactive intestinal peptide increases interleukin 6 production by astrocytes through the stimulation of the cAMP-protein kinase A pathway, an effect that is reproduced by cAMP analogues.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗