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Biomedical subjects

F Coceani

Publications and source records attributed to F Coceani.

At least 37 records · Page 2Linked to original sources
PubMed1996

Inhibition of the contraction of the ductus arteriosus to oxygen by 1-aminobenzotriazole, a mechanism-based inactivator of cytochrome P450.

1. We have proposed that contractile tension of the ductus arteriosus is sustained by a cytochrome P450-linked mechanism acting as a limiting step in the synthesis of endothelin-1 (ET-1). In the present study, we have used the isolated ductus from near-term foetal lambs and guinea-pigs to investigate the effect on both muscle tone and ET-1 formation of 1-aminobenzotriazole (ABT), a suicide substrate for mono-oxygenase reactions. 2. ABT relaxed the lamb ductus at rest (2.5% O2) and during the oxygen contraction (15 to 95% O2). The effect was seen at 40 microM, and at 0.8 mM active tone was almost completely abolished. ABT (1 mM) also reversed the oxygen contraction in the guinea-pig ductus. 3. In the lamb ductus, the ABT response was not affected by removal of the endothelium or by treatment with 2.8 microM indomethacin (at 2.5% O2) and the ensuing contraction. 4. At both low and high concentration, ABT relaxed marginally, or not at all, the potassium-contracted (55 mM) ductus from either species. 5. ET-1 release from either the intact or endothelium-denuded lamb ductus tended to decrease in the presence of ABT (1 mM), whilst during the same treatment cyclic GMP content of the tissue remained unchanged. 6. We conclude that ABT relaxation is due to suppression of a contractile mechanism and not to activation of prostaglandin- and NO-mediated relaxing mechanisms. This contractile mechanism has a cytochrome P450-based mono-oxygenase reaction as a key component.

Animals↗
PubMed1996

Carbon monoxide-induced relaxation of the ductus arteriosus in the lamb: evidence against the prime role of guanylyl cyclase.

1. We have previously found that carbon monoxide (CO) potently relaxes the lamb ductus arteriosus and have ascribed this response to inhibition of a cytochrome P450-based mono-oxygenase reaction which sustains contractile tone. Our proposal, however, has been questioned on the evidence of findings in other blood vessels implicating the guanylyl cyclase-based relaxing mechanism as the target for CO. To investigate this issue further, we have carried out experiments in the isolated ductus from near-term foetal lambs and have examined the effect of CO concomitantly on muscle tone and cyclic GMP content, both in the absence and presence of guanylyl inhibitors, or during exposure to monochromatic light at 450 nm. 2. CO (65 microM) reversed completely, or nearly completely, the tone developed by the vessel in the presence of oxygen (30%) and indomethacin (2.8 microM). Cyclic GMP content tended to increase with the relaxation, but the change did not reach significance. Sodium nitroprusside (SNP), a NO donor, mimicked CO in relaxing the ductus. Contrary to CO, however, SNP caused a marked accumulation of cyclic GMP with levels being positively correlated with the relaxation. 3. Methylene blue (10 microM) reduced marginally the CO relaxation, whilst LY-83583 (10 microM) had an obvious, albeit variable, inhibitory effect. Basal cyclic GMP content was lower in tissues treated with either compound and rose upon exposure to CO. However, the levels attained were still within the range of values for tissues prior to any treatment. Furthermore, the elevation in cyclic GMP was not related to the magnitude of the CO relaxation. 4. Illumination of the ductus with monochromatic light at 450 nm reversed the CO relaxation and any concomitant increase in cyclic GMP. In the absence of CO, light by itself had no effect. 5. Ductal preparation with only muscle behaved as the intact preparations in reacting to CO, both in the absence and presence of guanylyl cyclase inhibitors, or during illumination. 6. We conclude that the primary action of CO in the ductus arteriosus is not exerted on the guanylyl cyclase heme and that cyclic GMP may only have an accessory role in the relaxation to this agent. This finding reasserts the importance of a cytochrom P450-based mono-oxygenase reaction for generation of tone and as a target for CO in the ductus.

Aminoquinolines↗
PubMed1995

Response of newborn and adult sheep to pyrogens: relation between fever and brain eicosanoid changes.

We investigated whether the weak febrile response to pyrogens in newborns is due to a diminished activation of the putative pyrogen mediator, prostaglandin (PG)E2. Indwelling cannulas in the third ventricle of lambs (age, 5-31 days) and adult ewes were used to collect cerebrospinal fluid (CSF) for radioimmunoassay of PGE2. Intravenous (i.v.) endotoxin caused a smaller increase in body temperature but a larger increase in CSF PGE2 in lambs compared to adults. PGE2 by intracarotid infusion raised body temperature in 5 of 7 trials in 3 lambs and in 4 of 4 trials in 1 adult. Endotoxin given intracerebroventricularly (i.c.v.) induced a rise in temperature and CSF PGE2 in the lamb but, in the adult, these responses were delayed and smaller. Interleukin-1 i.c.v. and PGE2 i.c.v. were weak pyretic agents at both ages. We conclude that the lamb's diminished febrile response to endotoxin i.v. is not caused by a lesser rise in CSF PGE2, rather it may be due, at least in part, to reduced responsiveness to this putative mediator. Regardless of age, the sheep differs from other species in that pyrogen/PGE2 coupling occurs primarily at a site in brain that is better accessible from blood than CSF.

Animals↗
PubMed1995

Involvement of endothelin-1 in hypoxic pulmonary vasoconstriction in the lamb.

1. Using isolated pulmonary resistance vessels from mature fetal lamb and chronically instrumented lambs (8-17 days old), we have examined whether hypoxic pulmonary vasoconstriction is sustained by activation of a constrictor mechanism or suppression of a dilator mechanism. 2. Hypoxia contracted both arteries and veins in vitro, and the contraction was greater with the former. After removing the endothelium, arteries responded faster to hypoxia, but the magnitude of the response remained unchanged. 3. Hypoxic arteries, unlike normally oxygenated arteries, did not contract with either indomethacin (2.8 microM) or N omega-nitro-L-arginine methyl ester (L-NAME, 100 microM). The same vessels relaxed with sodium nitroprusside (SNP, 0.001-10 microM) but not with bradykinin (0.1-100 nM). 4. Endothelin-1 (ET-1, 0.01-10 nM) contracted isolated arteries and veins under normoxic and hypoxic conditions. In both vessels, the contraction was fast in onset and subsidence, and was inhibited by the ETA receptor antagonist BQ123 (1 microM). The ET-1 precursor, big ET-1 (100 nM), also contracted arteries and veins, but compared with ET-1 its action was slower in development. Big ET-1 contraction, unlike ET-1 contraction, was curtailed by the inhibitor of the ET-1-converting enzyme, phosphoramidon (50 microM). 5. ET-1 (0.1-10 nM) had no effect on isolated arteries precontracted with a thromboxane A2 (TXA2) analogue (ONO-11113) and treated with BQ123 (10 microM). Under the same conditions, ET-1 relaxed the veins. Accordingly, in the absence of BQ123 treatment, the selective ETB receptor agonist IRL-1620 (0.1-100 nM) relaxed the contracted veins but not the arteries. 6. BQ123 (10 microM) inhibited the constriction of isolated arteries and veins to hypoxia. Likewise, in the conscious lamb a bolus of BQ123 (0.4 mg kg-1, injected into the pulmonary artery) curtailed the rise in pulmonary vascular resistance (Rpa) brought about by alveolar hypoxia without changing significantly systemic vascular resistance (Rao). Under normoxia, Rpa was insignificantly affected by BQ123. 7. The results indicate that pulmonary resistance arteries are more susceptible to hypoxia than the veins, and that hypoxic vasoconstriction does not require an intact endothelium to occur. Hypoxic tone is ascribed primarily to intramural generation of ET-1, while removal of the tonic action of a relaxant may only have an accessory role in the response.

Animals↗
PubMed1995

Pyrogen - prostaglandin coupling in the pathogenesis of fever: evidence against a role for nitric oxide.

There is much debate on the mechanism by which blood-borne pyrogens trigger prostaglandin E2 (PGE2) synthesis in brain and fever. This investigation was undertaken to determine whether nitric oxide qualifies as a signal transducer for pyrogens at the interface between blood and brain. Experiments were carried out in vitro and in vivo using, respectively, preparations of cerebral tissue and microvessels from the rat, and the conscious, chronically instrumented cat. In vitro preparations produced PGE2 and its production increased during a 30-min treatment with interleukin 1 (brain tissue) or endotoxin (microvessels). In addition, both pyrogens increased cyclic GMP levels in cerebral microvessels. In both brain tissue and microvessels, NG-nitro-L-arginine had no effect on basal PGE2 release, while it curtailed the pyrogen-stimulated release. The same treatment reduced the cyclic GMP accumulation brought about by pyrogens in the microvessels. Conversely, in the conscious cat, inhibitors of nitric oxide synthesis (NG-monomethyl-L-arginine, NG-nitro-L-arginine) had no effect on fever and the concomitant elevation of PGE2 in cerebrospinal fluid, regardless of the pyrogen used (endotoxin, interleukin 1) and the route of administration (intravenous, intracerebroventricular). We conclude that nitric oxide may serve as a pyrogen mediator in brain. This mediator function, however, is seemingly not important in the development of fever.

Animals↗
PubMed1994

Endothelium-denuded pulmonary resistance arteries from the fetal lamb: preparation and response to vasoactive agents.

A method was developed for preparing endothelium-denuded resistance arteries (mean internal diameter, 176 microns) from the term fetal lung to be used for tests in vitro. The endothelium was removed mechanically by passing a sandpaper-polished cat whisker through the lumen. Ultrastructurally, the preparation had a well-preserved internal elastic lamina which was facing the lumen without any endothelium superimposed. Its response to contractile agents (excess potassium, a thromboxane A2 analogue, endothelin-1) tended to be greater compared to the intact artery. Conversely, the relaxation to acetylcholine was abolished in the endothelium-denuded artery and, in its place, a modest contraction ensued. Sodium nitroprusside relaxation, unlike acetylcholine relaxation, was affected insignificantly by endothelium denudation. This preparation, in combination with the preparation of the intact resistance artery, is a useful, new tool for studying local factors responsible for pulmonary hemodynamic control in utero and through the transitional period at birth.

Acetylcholine↗
PubMed1994

Occurrence of endothelium-derived relaxing factor--nitric oxide in the lamb ductus arteriosus.

To determine whether the ductus arteriosus can form endothelium-derived relaxing factor--nitric oxide, we used isolated ductal strips from near-term fetal lamb and examined their response to bradykinin (a nitric oxide stimulator), L-arginine (a nitric oxide precursor), and agents interfering with the synthesis (N omega-nitro-L-arginine) and action (methylene blue) of nitric oxide. Bradykinin relaxed the indomethacin-contracted ductus dose dependently from a threshold of about 10(-10) M, and peak relaxation was greater at high (176-210 mmHg; 1 mmHg = 133.3 Pa) than low (15-25 mmHg) PO2. Bradykinin relaxation was nearly completely or completely abolished in endothelium-denuded preparations and, in its place, there was often a small contraction. Pretreatment with nitric oxide inhibitors also prevented, in part (methylene blue, 1 microM) or in full (N omega-nitro-L-arginine, 100 microM), the relaxant effect of bradykinin. Paradoxically, L-arginine (10 microM) had an inhibiting rather than an enhancing effect on the bradykinin relaxation. N omega-Nitro-L-arginine (100 microM) and methylene blue (1-100 microM) contracted by themselves the untreated ductus, and their action persisted after removal of the endothelium. These findings indicate the presence in the ductus arteriosus of a nitric oxide based relaxing mechanism, which may supplement prostaglandin E2 in keeping the vessel patent in the fetus. This mechanism may, on one hand, afford protection against nonsteroidal anti-inflammatory drugs in utero and may, on the other hand, complicate the management of prematures with persistent ductus and account for failures of the indomethacin therapy.

Animals↗
PubMed1994

Cytochrome P450 during ontogenic development: occurrence in the ductus arteriosus and other tissues.

Our previous investigations have implicated a cytochrome P450 mechanism in the oxygen contraction of the ductus arteriosus and, by extension, in the closure of the vessel at birth. This study was undertaken in fetal and newborn sheep to characterize the ductal cytochrome and gather insight into its operation. Other tissues, vascular and extravascular, were used as a reference. Benzo[a]pyrene hydroxylation (a marker for the 3-methylcholanthrene-inducible isozyme) and aminopyrine N-demethylation (a marker for the glucocorticoid-inducible isozyme) had insignificant activity in the ductus and aorta from fetal sheep, and no increase was noted after exposing the animal in utero to beta-naphthoflavone or dexamethasone, both alone and in combination with phenobarbital. However, dexamethasone and, particularly, dexamethasone plus phenobarbital produced a variable constriction of the fetal ductus. No monooxygenase activity was found in the naturally closing ductus of the newborn. Conversely, both enzyme reactions were measurable in the fetal liver, and they became more active after treatment with the inducers or at birth. Scanning immunoelectron microscopy of cultured endothelial and muscle cells from both ductus and aorta showed specific gold labelling for the glucocorticoid-inducible cytochrome P450 only in ductal muscle. By transmission electron microscopy, this immunoreactivity was located along the sarcolemma and in the sarcoplasmic reticulum. These findings indicate the presence in the ductus arteriosus of a cytochrome P450 belonging to the 3A subfamily. However, considering the uneven action of the inducers on enzyme activity in ductal tissue and muscle tone, the role of this cytochrome in closure of the vessel at birth remains to be ascertained.

Aging↗
PubMed1994

EDRF in pulmonary resistance vessels from fetal lamb: stimulation by oxygen and bradykinin.

Endothelium-derived relaxing factor-nitric oxide (EDRF-NO) has been studied in isolated, pulmonary resistance vessels from term fetal lambs at a fetal (21 +/- 0.2 mmHg) and neonatal (69 +/- 0.4 mmHg) PO2. Bradykinin dose dependently (0.1-100 nM) relaxed arteries and veins that had been precontracted with a thromboxane A2 analogue. Their response did not differ at low PO2, whereas the response of the arteries was greater at high PO2. Sodium nitroprusside was almost as potent as bradykinin on the arteries, but its action did not vary with PO2. Acetylcholine also relaxed the arteries at higher concentrations (0.1-100 microM). N omega-mono-methyl-L-arginine (L-NMMA) and N omega-nitro-L-arginine methyl ester (L-NAME) (both at 100 microM) weakly contracted arteries at low PO2. The contraction to L-NAME, but not L-NMMA, increased with the PO2. In the arteries, L-NAME had no effect on bradykinin relaxation at low PO2, whereas it was an inhibitor at high PO2. Conversely, L-NMMA slightly inhibited bradykinin relaxation regardless of PO2. In the veins, L-NAME transiently increased basal tone and inhibited bradykinin relaxation at either PO2. Indomethacin (2.8 microM) had no effect on arteries at low PO2, whereas it was a constrictor at high PO2. No indomethacin constriction occurred in the veins. We conclude that fetal pulmonary resistance vessels possess an EDRF-NO relaxing mechanism that is stimulated by bradykinin. In the arteries, this mechanism is more effective at high PO2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Prostaglandin E2 in cerebrospinal fluid of fetal and newborn sheep: central versus peripheral source.

During the perinatal period, prostaglandin (PG) E2 levels show parallel changes in cerebrospinal fluid (CSF) and blood which may be important for the adaptation of the fetus to extrauterine life. It is not known, however, whether PGE2 in the CSF originates from a local or a peripheral source. Experiments were carried out in term fetal and newborn sheep chronically instrumented with a cannula inside the third ventricle and vascular lines. Indomethacin was given intracerebroventricularly (i.c.v.) (50 or 100 micrograms at hourly intervals), alone or in combination with intravenous (i.v.) PGE2 (1 or 1.5 micrograms/kg/min). In the fetus, i.c.v. indomethacin reduced PGE2 levels in both CSF and plasma. Conversely, no significant change was noted at either site when indomethacin was given i.c.v. to the newborn. At both ages, PGE2 increased in the CSF during i.v. infusion of the compound, but this elevation was proportionately smaller than in plasma. We conclude that, in the perinatal period, brain and peripheral circulation function as separate compartments with respect to PGE2, though there is passage of the compound across the blood-brain barrier. Results provide indirect evidence that perinatal brain produces PGE2 in measurable amounts.

Animals↗
PubMed1993

Interleukin-6 and tumor necrosis factor in cerebrospinal fluid: changes during pyrogen fever.

Several peptides (cytokines), viz., interleukin-1 (IL-1), interferon-alpha (IFN-alpha), interleukin-6 (IL-6), tumor necrosis factor (TNF), are formed in response to conditions causing tissue inflammation or damage and are implicated in reactive changes of the host, including fever, while IL-1 has been considered an important mediator of fever, the other cytokines, specifically IL-6 and TNF, have recently acquired prominence. The present study extends earlier research on IL-1 and addresses the question of the role of IL-6 and TNF in the genesis of fever. Experiments were conducted in the conscious cat, and IL-6 and TNF were assayed concomitantly in cerebrospinal fluid (CSF) from the third ventricle using specific bioassays. In the absence of fever, IL-6 was usually below the threshold of the assay (4-32 pg/ml), while TNF appeared measurable (424 +/- 57 pg/ml) in most experiments. A single intravenous injection of endotoxin (bolus) or continuous infusion of IL-1 at doses eliciting a sustained fever increased CSF levels of IL-6, but had no effect on concentrations of TNF. Intracerebroventricular injection of a pyrogenic dose of endotoxin led to an elevation of TNF and IL-6 and, in either case, the effect was manifest during the latent period before the fever. In addition, by the same route, IL-1 caused a rise in IL-6. We conclude that brain is intrinsically capable of producing both IL-6 and TNF depending on the site of challenge. However, since IL-6 CSF levels are elevated regardless of the site of pyrogen injection, IL-6 lends itself better to a role in the pathogenesis of fever.

Animals↗
PubMed1993

Eicosanoids in third ventricular cerebrospinal fluid of fetal and newborn sheep.

A method to serially sample cerebrospinal fluid (CSF) from the third ventricle of chronically catheterized fetal and newborn sheep was developed. Either sampling cannulas of preset lengths ("fixed-probe" technique) or a single cannula that could be positioned at the desired depth ("roving-probe" technique) was used. The roving probe proved superior because free CSF flow was obtained in seven of ten animals after surgery compared with two of nine animals implanted with a fixed probe. CSF (5 animals) and plasma (7 animals) was collected serially from 2 wk before to 2 wk after birth, including the time around labor. Prostaglandin E2 (PGE2) levels (means +/- SE) were significantly higher in CSF (366 +/- 120 pg/ml; n = 5) and plasma (520 +/- 69 pg/ml; n = 7) before the day of delivery than in the same animals after birth. During labor, CSF and plasma PGE2 levels increased significantly to 1,428 +/- 643 pg/ml in CSF and to 2,015 +/- 414 pg/ml in plasma. However, by 1 h after birth, PGE2 had fallen to 366 +/- 165 pg/ml in CSF and to 338 +/- 106 pg/ml in plasma; levels similar to those observed in the fetus before labor. PGE2 continued to decrease precipitously and, at 24 h of age, levels were significantly less than those observed in the fetus. PGE2 levels were near the limit of detection of the assay in CSF (< 5 pg/ml) and were 49 +/- 10 pg/ml in plasma. In contrast, CSF thromboxane B2 (n = 2) and total peptidoleukotriene content (n = 4) showed little change during labor or after birth.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Eicosanoid formation in the rat cerebral cortex. Contribution of neurons and glia.

Despite the extensive literature on brain eicosanoids, no information is available on the cellular source of individual compounds in the mature organ and the relative contribution of different cell types to the total synthetic product. To address this problem, neurons and glia were isolated from the cerebral cortex of the adult rat by a process comprising, in order, trypsinization, selective sieving, differential centrifugation, and density gradient centrifugation. Enrichment of cells in the appropriate fractions was verified by morphological, immunocytochemical, and biochemical criteria. Both neuron- and glia-rich fractions retained synthetic activity throughout the period of incubation (max. 60 min). Among the eicosanoids examined, prostaglandin (PG) E2 was the predominant compound, followed by leukotriene (LT) E4 and thromboxane (TX) B2, whereas LTC4 occurred in minimal amounts. Although the rank order of eicosanoids did not vary with the cell type, absolute values of PGE2 and TXB2 were greater with neurons. PGE2 synthesis was increased by supplementation of the medium with arachidonic acid (2.6 microM), whereas indomethacin (5.6 microM) had the opposite effect. Conversely, LT synthesis was not altered by arachidonic acid and was only marginally reduced by the 5-lipoxygenase inhibitor, U-60,257 (10 microM). Several agonists (12-O-tetradecanoyl-phorbol-13-acetate, TPA; Ca ionophore A23187; platelet-activating factor; endotoxin; recombinant IL-1) were tested on both neuron- and glia-rich fractions but none of them had an effect. We conclude that freshly isolated neurons and glia are viable insofar as the basal rate of eicosanoid synthesis is concerned. No qualitative difference was noted between the two cell types in the spectrum of products formed and the spectrum itself accorded with early data on the biosynthetic activity of the intact tissue in vivo. Our isolation procedure appears useful for the analysis of the cellular source of eicosanoids under resting conditions, although it cannot be applied to the study of the site and mode of action of activators.

Animals↗
PubMed1992

Evidence for an effector role of endothelin in closure of the ductus arteriosus at birth.

The ductus arteriosus is a special muscular shunt that in the fetus allows blood to bypass the unexpanded lungs. It closes rapidly after birth and this event is initiated by the physiologic rise in blood oxygen tension. Endothelin-1 has been proposed by us as a local mediator for oxygen after demonstrating that it is formed within the ductus and is a potent ductus constrictor. To confirm this possibility, we have now measured the release of endothelin-1 from the isolated ductus of near-term fetal lambs at different oxygen concentrations of the medium. In addition, using the same preparation, we have examined the effect on contractile tone of compounds interfering with the synthesis (phosphoramidon, 50 microM) and action (BQ123, 1 microM) of endothelin-1. We report that release of endothelin-1 from the ductus tends to increase with the oxygen concentration up to a value mimicking the neonatal condition. Phosphoramidon and, to a greater degree, BQ123 inhibit the contraction of the vessel to oxygen. These results implicate endothelin-1 as the effector agent for oxygen in the ductus and, by extension, assign to this peptide a critical role in the closure of the vessel at birth.

Animals↗
PubMed1992

Interleukin-1 receptor antagonist: effectiveness against interleukin-1 fever.

Conscious cats were used to examine the effectiveness of the interleukin-1 receptor antagonist against the fever induced by interleukin-1 and endotoxin. Although inactive by itself, the antagonist (three 1-micrograms bolus injections at 10-min intervals), injected into the third ventricle, attenuated the febrile response to a subsequent intracerebroventricular bolus of interleukin-1. The rise in prostaglandin E2 levels in cerebrospinal fluid, which is a characteristic feature of fever, was curtailed as well. The interleukin-1 antagonist had little or no inhibitory effect on the response to an intracerebroventricular bolus of endotoxin, even though a higher dose was employed (2-micrograms bolus injections given three times at 10-min intervals and six times at 30-min intervals, respectively, before and after endotoxin administration). At either dosage, the intracerebroventricular antagonist was completely ineffective against an intravenous bolus injection of interleukin-1 or endotoxin and both fever and prostaglandin E2 elevation developed unabated. We conclude that brain receptors mediating the pyrogenic action of centrally injected interleukin-1 are susceptible to the antagonist. The same receptors, however, are seemingly not activated by systemic pyrogens. Our findings are consistent with the concept of circulating interleukin-1 acting outside the blood-brain barrier in the normal sequence of fever.

Animals↗