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Biomedical subjects

P Navarra

Publications and source records attributed to P Navarra.

At least 37 records · Page 2Linked to original sources
PubMed1999

Inhibition of heme oxygenase in the central nervous system potentiates endotoxin-induced vasopressin release in the rat.

Previous in vitro studies have shown that increases in endogenous carbon monoxide (CO) generation via activation of the enzyme heme oxygenase (HO) within the rat hypothalamus are associated with the reduced release of the neuropeptides, vasopressin (AVP) and oxytocin, while evidence concerning corticotrophin-releasing hormone (CRH) is controversial. The present study investigated whether there is also a functional relationship between the HO-CO pathway and AVP and corticosterone (Cort) in vivo. Male Wistar rats were challenged with bacterial lipopolysaccharide (LPS) at doses producing significant activation of the hypothalamo-pituitary-adrenal (HPA) axis. LPS was given alone or after pretreatment with the HO inhibitor Sn-protoporphyrin-9 (SnPP9). The latter was injected either intraperitoneally (i.p.) or by intracerebroventricular (i.c.v.) route. SnPP9 given i.p. failed to modify either basal or LPS-stimulated levels of AVP and Cort. On the contrary, i.c.v. SnPP9 strongly potentiated LPS-induced AVP release and significantly enhanced basal serum Cort levels, although it failed to potentiate stimulation by LPS. The LPS + i.c.v. SnPP9 also significantly reduced the hypothalamic stores of AVP compared to controls, correlating with increased circulating levels of AVP. Taken collectively, these data are in concordance with previous in vitro observations showing that the HO-CO pathway acts centrally to attenuate endotoxin-stimulated AVP release, while having less effects on the pituitary-adrenal axis.

Animals↗
PubMed1999

Electromotive versus passive diffusion of mitomycin C into human bladder wall: concentration-depth profiles studies.

The objectives of these investigations were: (a) to make a preliminary study to assess concentration-depth profiles of mitomycin C (MMC) in the bladder wall at specified time intervals after passive diffusion (PD); and (b) to conduct a major study to compare concentration-depth profiles after PD and electromotive drug administration (EMDA) of MMC. Full thickness sections of viable human bladder wall were placed in two-chamber cells with urothelium exposed to donor compartments containing 40 mg of MMC in 100 ml of 0.96% NaCl solutions and with serosa-facing receptor compartments containing 0.9% NaCl solutions. In the preliminary study during each of nine experimental sessions, five sections of bladder wall were individually exposed to MMC for either 5, 15, 30, 45, or 60 min. In the major study, an anode and a cathode were sited in the donor and receptor compartments, and 14 paired experiments--current (20 mA)/no current--were conducted over a 30-min period. Bladder wall sections were cut serially into 40-microm slices parallel to the urothelium and analyzed by high-performance liquid chromatography for MMC concentration (microg/g wet tissue weight). Tissue viability and morphology and MMC stability were assessed by trypan-blue exclusion test, histological examination, and mass spectrometry analysis. In the preliminary study (PD only), mean MMC concentrations (microg) at 5, 15, 30, 45, and 60 min were: (a) for urothelium, 15.3, 60.0, 58.2, 60.1, and 57.8, respectively; (b) for lamina propria, 2.2, 18.9, 19.3, 16.1, and 17.3, respectively; and (c) for muscularis, 0.4, 2.0, 1.8, 1.3, and 2.4, respectively. In the comparative study, MMC concentrations and coefficients of variation (CV) were as follows: (a) for urothelium after PD, 46.6 with CV = 69%, and after EMDA, 170.0 with CV = 43% (P < 0.0001); (b) for lamina propria after PD, 16.1, with CV = 60%, and after EMDA, 65.6 with CV = 29% (P < 0.0001); and (c) for muscularis after PD, 1.9 with CV = 82%, and after EMDA, 15.9 with CV = 82% (P < 0.0005). All of the bladder sections remained viable, and the chemical structure of MMC was unchanged. It was concluded that EMDA significantly enhances MMC transport into all of the layers of the bladder wall, and sections of viable human bladder are a reliable tool for assessing different modes of drug delivery.

Biological Transport↗
PubMed1999

Bacterial lipopolysaccharide increases prostaglandin production by rat astrocytes via inducible cyclo-oxygenase: evidence for the involvement of nuclear factor kappaB.

This study was set to investigate the mechanisms through which bacterial lipopolysaccharide (LPS) stimulates prostaglandin (PG) production in rat astrocytes. Primary cultures of rat hypothalamic astrocytes were established. Cells were treated with LPS alone or LPS plus antagonists of various pathways, and the subsequent changes in cyclo-oxygenase (COX) activity were monitored by measuring a COX end product, PGE2, released into the incubation medium. It was found that (i) LPS produced a concentration-dependent increase in PGE2 release from astrocytes. The potency of LPS was significantly increased by the addition of serum into the incubation medium; (ii) after 24 h of incubation, inducible COX (COX-2) accounts for most of the LPS-stimulated PG production, as the latter was markedly reduced by dexamethasone and the specific COX-2 inhibitor NS 398; and (iii) nuclear factor kappaB appears to play a role in the activation of COX-2 induced by LPS, since certain inhibitors of this transcription factor were able to antagonize, at least in part, the effects of LPS on PGE2 release.

Animals↗
PubMed1999

No cardiovascular effects of single-dose pseudoephedrine in patients with essential hypertension treated with beta-blockers.

OBJECTIVE: The use of the decongestant pseudoephedrine has been cautioned in patients with arterial hypertension, due to the possible rise in blood pressure induced by the sympathostimulatory properties of the drug. This effect could be enhanced in hypertensives treated with beta-blockers, in whom the vasoconstrictor effect of alpha-adrenergic stimulation is unbalanced. The purpose of this study was to investigate the cardiovascular response to pseudoephedrine in hypertensive patients treated with different types of beta-blockers. METHODS: We recruited 29 (18 males) mild-to-moderate essential hypertensive patients [mean age 49(2) years] in a randomized, placebo-controlled, crossover trial. All participants received either placebo, or a nonselective (propranolol 160 mg once daily) or a selective (atenolol 100 mg once daily) beta-blocker for 1 week. At the end of each period, all patients received a single oral dose of pseudoephedrine (60 mg) and their blood pressure and heart rate were monitored at repeated intervals for 2 h. RESULTS: After 1 week of propranolol or atenolol, patients had significantly lower systolic blood pressure and heart rate than after placebo, whereas diastolic blood pressure was not significantly modified. The acute administration of pseudoephedrine did not change systolic and diastolic blood pressure and heart rate from baseline at the end of any of the treatment periods. CONCLUSIONS: A standard oral dose of pseudoephedrine does not significantly affect blood pressure values in hypertensive patients treated with beta-blockers, and therefore may be safely used in this subset of patients.

Adrenergic alpha-Agonists↗
PubMed1999

Antiphospholipid antibodies inhibit prostaglandin release by decidual cells of early pregnancy: possible involvement of extracellular secretory phospholipase A2.

OBJECTIVE: To investigate the effect of antiphospholipid antibodies on eicosanoid production by human decidual cells and the in vitro interaction between antiphospholipid antibodies and secretory phospholipase A2. DESIGN: Cultures of human decidual cells from early pregnancy. SETTING: All decidual specimens were obtained from the Obstetrics and Gynecology Department of the Catholic University, Rome, Italy. PATIENT(S): Patients were undergoing operative laparoscopy for extrauterine pregnancy, with a period of amenorrhea ranging from 6 to 9 weeks. INTERVENTION(S): Decidual samples were collected at laparoscopy by routine uterine curettage. MAIN OUTCOME MEASURE(S): Decidual cells were incubated with antiphospholipid antibodies, and eicosanoids (prostaglandin [PG] E2, PGF2alpha, and thromboxane B2) were assayed by RIA after 24 hours of culture. In vitro interactions between antiphospholipid antibodies and secretory phospholipase A2 were investigated with use of a modified ELISA for phospholipase A2. RESULT(S): Antiphospholipid antibodies reduced eicosanoid release from decidual cells in a dose-dependent fashion. In vitro assays showed that antiphospholipid antibodies bound secretory phospholipase A2 and that a competition occurred between antiphospholipid antibodies and secretory phospholipase A2 for the common substrate cardiolipin. CONCLUSION(S): In light of the critical role played by eicosanoids in decidual function, we suggest that an interaction between antiphospholipid antibodies and secretory phospholipase A2 occurring in vivo might impair important cellular communications at the decidual level in the antiphospholipid antibody syndrome.

Antibodies, Anticardiolipin↗
PubMed1999

The effect of growth hormone secretagogues and neuropeptide Y on hypothalamic hormone release from acute rat hypothalamic explants.

Growth hormone (GH) secretagogues (GH-releasing peptides and their non-peptide analogues) stimulate growth hormone release via specific G-protein coupled receptors both directly from the pituitary gland and through stimulation of the hypothalamus. The exact mechanism of action in the hypothalamus is not known. The presence of endogenous GH releasing hormone (GHRH) seems to be necessary for the in-vivo actions of growth hormone secretagogues (GHSs), but data suggest that further factors must be involved as well. The effect of GHSs is not entirely specific for the GH axis; they release prolactin and stimulate the hypothalamo-pituitary-adrenal axis causing elevations in circulating ACTH and cortisol levels in both animal and human studies. Recently, it has also been suggested that GHSs stimulate hypothalamic neuropeptide Y (NPY) neurones. In the present study, we have therefore investigated the direct effect of several GHSs (GHRP-6, hexarelin and the non-peptide analogues L-692, 429 and L-692, 585) on GHRH, somatostatin (SS), corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) release in vitro in an acute rat hypothalamic incubation system. We also assessed the effect of NPY on GHRH, SS and AVP release. Freshly removed hypothalami were incubated in control media for 20 min and then in 1-4 consecutive 20-min periods in each of the test substances at different concentrations. There was no significant change in either the basal or potassium-stimulated release of GHRH or SS at low concentrations of any of the secretagogues; however, at millimolar doses a paradoxical inhibition of GHRH was observed with GHRP-6, hexarelin and L-692 585 (data are expressed as the ratio of treated to preceding basal release; at 20 min control group: 0.97+/-0.02, GHRP-6: 0.55+/-0.04, P<0.001 compared to control group; hexarelin: 0. 56+/-0.06, P<0.001, L-692,585: 0.70+/-0.03, P<0.001), while SS was stimulated after 60 or 80 min (at 80 min control: 0.80+/-0.03, hexarelin: 1.23+/-0.07, P<0.05 and L-692,585: 1.37+/-0.11, P<0.05). GHSs stimulated hypothalamic AVP release (at 20 min control: 0. 99+/-0.06 ratio to basal release, 10-4 M concentration of GHRP-6: 6. 31+/-1, P<0.001, hexarelin: 1.88+/-0.4, P<0.01, L-692,429: 1.90+/-0. 5, P<0.05 and L-692,585: 2.34+/-0.96, P<0.01), while no stimulatory effect was found on CRH release. NPY significantly stimulated SS and inhibited basal and potassium-stimulated GHRH release, while potentiating potassium-evoked AVP secretion. The Y1 receptor antagonist BIBP 3226 did not inhibit the effects of NPY on SS, GHRH or AVP release. We therefore conclude that, in this in-vitro rat hypothalamic incubation model, growth hormone secretagogues stimulate the release of AVP but have no effect on either GHRH, SS or CRH at low doses; at high doses paradoxically they inhibit the hypothalamic GH axis similar to in-vivo data in the rat. We speculate that these effects might be mediated by NPY.

Animals↗
PubMed1999

Paracrine regulation of insulin-like growth factor I (IGF-I) an IGF-II on prostaglandins F2alpha and E2 synthesis by human corpus luteum in vitro: a possible balance of luteotropic and luteolytic effects.

The existence of a complete intraovarian insulin-like growth factor (IGF) system replete with ligands, receptors, and binding proteins has been demonstrated as well as the ability of IGF-I to positively affect steroidogenesis in human granulosa cells. Furthermore, we recently showed that IGF-I and IGF-II stimulate progesterone secretion by human luteal cells. As the PGs, PGE2 and PGF2alpha, are classically known to have luteotropic and luteolytic effects, we wanted to determine whether the IGFs could affect the human luteal phase by influencing the PG system. For this reason, human luteal cells were cultured for different times (12, 24, and 48 h) with IGF-I, IGF-II (10-100 ng/mL), and GH (100 ng/mL), and both PGs were assayed in the medium culture. We found that both IGF-I and IGF-II were able to stimulate PGE2 synthesis in a time- and dose-dependent way, whereas they both inhibited PGF2alpha production. GH, too, significantly reduced PGF2alpha synthesis; this effect was IGF-I mediated because it was reverted by increasing dilutions of an anti-IGF-I antibody. On the contrary, no GH effect was observed on PGE2 production. In conclusion, based on these data and on our previous results, we speculate that IGFs could influence luteal steroidogenesis through PG system.

Adult↗
PubMed1998

Hypothalamic interleukin-1 in physiology and pathology.

The occurrence of interleukin-1 (IL-1) in the brain is usually associated with pathological events of the central nervous system (CNS), although there is evidence that the cytokine may also play a role in physiological processes. The ability of IL-1 to induce a damage in the CNS is dependent on the type of cell producing the cytokine and the length of exposure; on this regard, it is possible to distinguish between the minutes-to-days and the days-to-years time-frames. While the long-term action of IL-1 in the CNS is unambiguously associated with the activation of glial cells as well as the occurrence of chronic disorders such as Alzheimer's disease and AIDS-related dementia, it remains to be established whether glial cells, 'interleukinergic' neurons or both cell types are involved in CNS responses to acute noxiae, such as physical stress (restrain stress, nociceptive stimulation) or immune-inflammatory challenges.

AIDS Dementia Complex↗
PubMed1998

Bacterial lipopolysaccharide increases interleukin-6 and prostaglandin release in rat cortical type I astrocytes by different mechanisms: role of anti-inflammatory agents.

LPS stimulated IL-6 release in a concentration-dependent manner from rat cortical type I astrocytes. This stimulatory action was completely abolished by Dexamethasone (DEX), but was not affected by indomethacin (IND), a 5-cyclooxigenase inhibitor. LPS-induced IL-6 release was partially inhibited by BW 4AC, a 5-lipoxygenase inhibitor. LPS concentration-dependently increased the release of PGE2 from type I astrocytes, an effect completely inhibited by IND. To rule out the possibility that DEX was inhibiting LPS-induced IL-6 release by blocking IL-6 gene expression, we tested the effect of DEX on interleukin 1beta(IL-1)-induced IL-6 release. DEX slightly inhibited IL-1-induced IL-6 release, while IL-1 releasing action on IL-6 was significantly reduced by IND. The involvement of nitric oxide (NO) generation on LPS-induced IL-6 release was also studied. We found that L-NO-arginine, an inhibitor of nitric oxide synthase, concentration-dependently reduced LPS-induced IL-6 release in astrocytes. In conclusion, we provide evidence that LPS action on IL-6 and PGE2 release can be ascribed to the activation of different transduction mechanisms, which can be pharmacologically dissected with the aid of anti-inflammatory drugs.

Animals↗
PubMed1998

Endotoxin stimulates an endogenous pathway regulating corticotropin-releasing hormone and vasopressin release involving the generation of nitric oxide and carbon monoxide.

Although the administration of endotoxin in vivo activates the neuroendocrine stress axis in the process of crosstalk between the immune and endocrine axes, the direct application of endotoxin to the hypothalamus in vitro does not stimulate the release of the hypothalamic peptides controlling the hypothalamo-pituitary-adrenal (HPA) axis, corticotropin-releasing hormone (CRH) and vasopressin. The hypothesis has therefore been tested that endotoxin may also activate inhibitory pathways, specifically those involving the generation of nitric oxide (NO) and carbon monoxide (CO). Studies were performed on the isolated rat hypothalamus using endotoxin in the presence or absence of inhibitors of heme oxygenase (which generates CO) and nitric oxide synthase, and ferrous hemoglobin. Endotoxin alone decreased both CRH and vasopressin secretion from the hypothalamus. However, when applied together with a nitric oxide synthase inhibitor, the inhibitory effect on CRH was lost. Conversely, co-administration with heme oxygenase inhibitors transformed the inhibition of vasopressin to stimulation, while having no effect on the inhibition of CRH. Ferrous hemoglobin reversed the inhibition of vasopressin, but did not lead to stimulation. It is therefore concluded that endotoxin may stimulate endogenous pathways that lead to the generation of NO, which in turn inhibits CRH. In addition, it generates CO, which modulates the release of vasopressin. These gases are thus potential counter-regulatory controls to the activation of the HPA.

Animals↗
PubMed1998

Acute and subacute effects of endotoxin on hypothalamic gaseous neuromodulators.

Although two-way communication between the hypothalamus and the immune system in now well established, particularly for the hypothalamo-pituitary-adrenal axis, the role of the gaseous neurotransmitters nitric oxide (NO) and carbon monoxide (CO) is much less well understood in terms of hypothalamic function. These agents are an important part of the peripheral inflammatory response; and their synthetic enzymes, NO synthase (NOS) and heme oxygenase (HO), respectively, have been localized to the hypothalamic PVN and SON. The induced generation of both NO and CO leads to the suppression of CRH and vasopressin, the major stimulators of the HPA. Thus, the addition of hemin to hypothalamic explants is maximally active at 1 microM in attenuating the release of CRH and vasopressin, and this dose is also most effective in generating biliverdin and associated CO. CO generation is also able to stimulate cyclooxygenase to produce prostaglandin E2, an established intermediary in the cytokine-stimulated activation of the HPA. Finally, inducible NOS mRNA is specifically induced in the hypothalalmus in response to endotoxin, in parallel to interleukin-1. These data provide increasing evidence in favor of NO and CO as counterregulatory agents in the HPA response to immune activation.

Animals↗
PubMed1998

The relative contribution of constitutive and inducible cyclooxygenase activity to lipopolysaccharide-induced prostaglandin production by primary cultures of rat hypothalamic astrocytes.

In this study, we have compared the time-course effects of lipopolysaccharide (LPS) and interleukin-1beta on prostaglandin (PG) production by primary cultures of rat astrocytes. At variance with interleukin-1beta, LPS produced significant increases in PGE2 release after only 1 h of incubation, an effect unlikely to depend on new protein synthesis; the involvement of constitutive cyclooxygenase (COX-1) was therefore investigated. Experiments with acetylsalicylic acid showed that 80% of PGE2 production after 1 h of treatment with LPS is accounted for by COX-1; this figure decreases to about 30% after a 24-h treatment. The increase in PGE2 production occurring after a 24-h challenge with the endotoxin seems to involve the activation of phospholipase A2. In fact, LPS-stimulated PGE2 release was significantly reduced by a peptide from the primary sequence of lipocortin-1, peptide Ac2-26, which was previously shown to inhibit phospholipase A2 in several in vitro models.

Animals↗
PubMed1998

The generation of nitric oxide and carbon monoxide produces opposite effects on the release of immunoreactive interleukin-1beta from the rat hypothalamus in vitro: evidence for the involvement of different signaling pathways.

Both the cytokine, interleukin-1 (IL-1), and the gaseous neurotransmitters, nitric oxide (NO) and carbon monoxide (CO), have been implicated in the control of neuroendocrine functions, such as the release of CRH and luteotropic hormone-releasing hormone from the hypothalamus. Though increased levels of IL-1 in this brain region are unambiguously associated with enhanced CRH and reduced luteotropic hormone-releasing hormone release, the net effects of the two gases are still unclear, but in vivo and in vitro evidence suggests that the generation of NO and CO within the hypothalamus might counteract the stimulatory effects of IL-1 and bacterial lipopolysaccharide on the neuroendocrine stress axis. In this study, we have investigated the effects of NO and CO on the release of immunoreactive (ir)-IL-1beta from the rat hypothalamus in vitro. It was observed that the NO donor, sodium nitroprusside (SNP), stimulates ir-IL-1beta release under basal conditions, whereas the increase in CO levels obtained with hemin, the CO precursor through the heme oxygenase pathway, has no effect on basal ir-IL-1beta release but inhibits release stimulated by high K+ concentrations. The opposite effects of the two gases on cytokine release seemed to be caused by the activation of different signaling pathways, because: 1) SNP, but not CO-saturated solutions, is able to increase cyclic GMP levels in hypothalamic tissue; 2) CO-saturated solutions increase PGE2 production and release from the hypothalamic explants, whereas SNP has no effect; 3) SNP-stimulated ir-IL-1beta release is counteracted by a selective inhibitor of soluble guanylyl cyclase, LY 83583, but not by a cyclooxygenase inhibitor, indomethacin; and 4) conversely, indomethacin, but not LY 83583, reverses the inhibitory effect of hemin on K+-stimulated ir-IL-1beta release. It is concluded that NO and CO signal in the rat hypothalamus via the activation of soluble guanylyl cyclase and cyclooxygenase, respectively.

Animals↗
PubMed1997

Activation of heme oxygenase and consequent carbon monoxide formation inhibits the release of arginine vasopressin from rat hypothalamic explants. Molecular linkage between heme catabolism and neuroendocrine function.

Heme oxygenase (HO)-catalyzed degradation of cellular heme moieties generates biliverdin and equimolar amounts of carbon monoxide (CO), which has been implicated as a possible modulator of neural function. Technical difficulties preclude direct measurements of CO within intact nervous tissues; hence, alternative procedures are needed to monitor the formation and possible biologic functions of this gas. In the present study rat hypothalamic explants were found to generate 114 +/- 5 or 127 +/- 11 pmol biliverdin/hypothalamus/1 h (n = 3) upon incubation with 1 or 10 microM hemin, respectively. Ten micromolar zinc-protoporphyrin IX (Zn-PP-IX), a known inhibitor of HO, significantly decreased the degradation of 10 microM hemin from 127 +/- 11 to 26 +/- 11 pmol biliverdin/hypothalamus/1 h (n = 3; P < 0.01). Biliverdin was the principal product of HO-dependent heme degradation, as its possible conversion into bilirubin was precluded by hemin-dependent inhibition of biliverdin reductase. Basal or hemin-supplemented hypothalamic incubations were also shown to generate sizable amounts of propentdyopents (PDPs), reflecting HO-independent degradation pathways which do not liberate CO and cannot be inhibited by Zn-PP-IX. Plotting the ratio of biliverdin to PDPs thus provided an index of the efficiency with which hemin was degraded through biochemical pathways involving CO. Under the experimental conditions of our study, the biliverdin/PDPs ratio varied from 0 to 32 or 15%, depending on the absence or presence of 1 or 10 microM hemin respectively: this suggested that the formation of CO was most efficient at 1 microM hemin. Under these defined conditions, 1 microM hemin was also found to inhibit the release of arginine vasopressin (AVP) evoked by depolarizing solutions of KCl. A series of experiments showed that the effect of hemin was counteracted by Zn-PP-IX, and also by tin-mesoporphyrin IX, which is even more selective in inhibiting HO; it was also attenuated in the presence of the gaseous scavenger ferrous hemoglobin. Furthermore, the inhibition of AVP release could be reproduced by omitting hemin and by incubating hypothalami under CO, whereas treatment with biliverdin had no effect. This suggested that the release of AVP was suppressed by HO degradation of hemin, yielding CO as a modulator of hypothalamic function. These observations may be relevant to diseases characterized by inappropriate secretion of AVP and enzymatic disturbances affecting the synthesis of heme and the formation of CO through the HO pathway (e.g., acute intermittent porphyria or lead intoxication).

Animals↗
PubMed1997

Disruptions of the hypothalamo-pituitary-adrenal axis increase anticancer drug lethality in the rat.

We have previously shown that toxicity of the anticancer agent hydroxyurea (HU) in the rat is markedly increased by hypophysectomy or adrenalectomy. In this study, we investigated whether increased toxicity in ablated animals is a unique feature of HU or it is shared with other anticancer agents; the toxic effects of five such drugs have been compared in intact, hypophysectomized (HYX) and adrenalectomized (ADX) rats. Bis-chloroethyl-nitrosourea (BCNU, 5-10 mg/kg), busulfan (0.1-10 mg/kg), cyclophosphamide (25-125 mg/kg), 5-fluorouracil (15-75 mg/kg) and vindesine (0.1-0.5 mg/kg) were given to intact and endocrine-ablated rats, and lethality was recorded over 3 weeks. It was found that mortality was low or absent in intact rats, whereas (with the exception of HYX rats receiving the highest dose of busulfan) it was dramatically increased by both hypophysectomy and adrenalectomy. However, replacement treatments with long-acting tetracosactrin and corticosterone to HYX and ADX rats respectively afforded significant protection against BCNU toxicity only. We conclude that the integrity of the hypothalamo-pituitary-adrenal axis is needed to tolerate the toxicity of various anticancer drugs, although complex mechanisms appear to underlie such protective effect.

Adrenalectomy↗