PubMed Health⌕ Search

Biomedical subjects

M O Carruba

Publications and source records attributed to M O Carruba.

At least 37 records · Page 2Linked to original sources
PubMed1997

Tumor necrosis factor-alpha induces apoptosis in rat brown adipocytes.

Accumulating evidence demonstrates that adipose tissue is a major site of tumor necrosis factor-alpha (TNF-alpha) gene expression, which is markedly high in obese animals and may contribute to obesity-linked insulin resistance. We now report that recombinant murine TNF-alpha triggers the apoptotic degeneration of brown adipocytes differentiated in culture. Moreover, noradrenaline, which has been described as having trophic effects on brown fat and accelerating the differentiation of brown adipocytes, is capable of dose-dependently preventing the TNF-alpha-induced apoptosis of brown fat cells. Since obesity is characterized by greatly increased TNF-alpha production and reduced catecholaminergic activity, apoptosis was studied in the brown fat of genetically obese animals. In situ DNA fragmentation analysis revealed a larger number of apoptotic cells in the brown fat of obese (fa/fa) than in that of lean (+/+) Zucker rats. The exposure of obese rats to low temperatures for 7 days, which increases the sympathetic activity of brown adipose tissue, significantly reduces the number of apoptotic brown adipocytes. We hypothesize that TNF-alpha may play a significant role in the control of brown fat homeostasis.

Journal Article↗
PubMed1997

Inducible nitric oxide synthase in rat brown adipocytes: implications for blood flow to brown adipose tissue.

Exposure of rat brown adipocytes differentiated in culture to norepinephrine (NE) results in the production of nitrites (NO2-), the breakdown product of nitric oxide (NO). This production, which is blocked by actinomycin D1 is directly related to the duration of exposure to and dose of NE. Cytosol from NE-treated brown fat cells, but not from untreated cultures, catalyzed the Ca(2+)-independent conversion of L-arginine to L-citrulline, which could be significantly blocked by the specific nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester. Reverse transcriptase-PCR demonstrates that the addition of NE; selective beta 1-, beta 2-, or beta 3-adrenergic receptor agonists; or agents increasing cAMP production, such as forskolin, to brown adipocytes stimulates inducible NOS (iNOS) messenger RNA, which is present within 4 h after exposure. That iNOS is synthesized in brown fat cells is confirmed by immunoblotting using an antibody to the iNOS of mouse macrophages, Finally, in both brown adipose tissue (BAT) and brown adipocyte preparations from animals exposed to low temperature, iNOS messenger RNA and protein were expressed, and NOS activity was detectable; these findings were unlikely for room temperature-acclimated rats. We conclude that brown fat cells can express an inducible form of NOS similar to the iNOS of macrophages, and that its production is directly dependent on sympathetic activity in physiological conditions. NO generated by stimulation of iNOS in brown adipocytes may represent an important mechanism to modulate different BAT functions, among which is vasodilation of the BAT microcirculation.

Adipocytes↗
PubMed1996

Salbutamol antagonizes insulin- and sodium mercaptoacetate-induced but not 2-deoxy-D-glucose-induced hyperphagia.

The role of beta-adrenoreceptors in modulating feeding in glucoprivation- and lipoprivation-induced hyperphagias was studied in rats by measuring the efficacy of the selective beta2-adrenoreceptor agonist salbutamol to antagonize the hyperphagic response induced by injection of 2-deoxy-D-glucose (2-DG), insulin, or sodium mercaptoacetate (MA). 2-DG and insulin are blockers of glucose utilization, and their administration stimulates receptor cells that are selectively sensitive to central glucose availability. MA stimulates feeding in rats maintained on a fat-supplemented diet, by blocking fatty acid oxidation at different levels in the metabolic pathway. We found that salbutamol dose-dependently antagonized both the insulin- and MA-induced hyperphagia, with reductions in food intake up to 100% compared with rats treated with insulin or MA alone. On the contrary, salbutamol, even at the highest dose (15 mg/kg, IP), was completely ineffective against 2-DG-induced hyperphagia. The present results support the previously proposed notion that there are different neuronal or humoral circuits underlying the hyperphagic responses to the metabolic stimuli induced by glucoprivation (i.e., 2-DG and insulin administration), and they extend our knowledge on the effects of salbutamol on glucoprivic and lipoprivic control of feeding.

Adrenergic beta-Agonists↗
PubMed1996

Expression of nerve growth factor in brown adipose tissue: implications for thermogenesis and obesity.

The presence of nerve growth factor (NGF) and the ability of adrenergic stimulation to affect the rate of its synthesis in mouse, rat, and human brown adipose tissue (BAT) were investigated. Addition of conditioned medium, obtained from preconfluent and confluent brown adipocytes, to PC12 cells induced typical morphological changes similar to those due to NGF itself. Anti-NGF antibodies blocked this action. Moreover, NGF mRNA was detected by RT-PCR both in BAT and in brown adipocyte preparations. That NGF is synthesized in and released from brown fat cells was confirmed by immunoblotting. When the animals were exposed to low temperatures, NGF production declined. The effect of cold exposure could be mimicked by the addition of norepinephrine (NE) at day 4 or 8 (preconfluent and confluent cells, respectively). NE depletion obtained by reserpine injection induced a drastic increase of BAT NGF production. In both rat and human BAT, immunohistochemistry identified distinct anatomical structures that express the low affinity neurotropin receptor, termed p75NGFR. BAT production of NGF was higher in genetically obese rats and mice than in their lean counterparts, a difference that becomes more evident with age. Prolonged exposure to low temperature significantly decreased the BAT NGF synthesis also in obese animals. We conclude that NGF is synthesized in and released from brown fat cells, its production being inversely dependent on sympathetic activity, in both physiological and pathophysiological conditions, and increased in genetic animal models of obesity.

Adipose Tissue, Brown↗
PubMed1996

Functional studies of the first selective beta 3-adrenergic receptor antagonist SR 59230A in rat brown adipocytes.

The SS-enantiomer 3-(2-ethylphenoxy)-1-[(1S)-1,2,3,4-tetrahy dronaphth-1-ylaminol]-(2S)-2-propanol oxalate (SR 59230A) is proposed to be the first beta 3-adrenergic receptor antagonist. The present work shows that SR 59230A, unlike its inactive RR-enantiomer (SR 59483), antagonized a typical beta 3-adrenergic response in vitro, i.e., SR 58611A, the ethyl-[(7s)-7-[[(2R)-2-(3- chlorophenyl)-2-hydroxethyl]amino]-5,6,7,8-tetrahydronaphth- 2- yl]oxyacetate hydrochloride- or (-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one (CGP 12177)-stimulated synthesis of cAMP in rat brown adipose tissue membranes, with pKB values of 8.87 +/- 0.12 and 8.20 +/- 0.15. In addition, SR 59230A had no antagonistic effect on forskolin-induced cAMP accumulation in rat interscapular brown adipose tissue. SR 59230A, in contrast to the selective beta 1- and beta 2-adrenoceptor antagonists (+/-)[2-(3-carbamoyl-4-hydroxyphenoxy)-ethylamino]- 3-[4(1-methyl-4-trifluoromethyl-2-imidazolyl)-phenoxy]-2 propanol and erythro-(+/-)-1-(7-methylindan-4-yloxy)-3-isopropylaminob utan- 2-ol-hydrochloride did not counteract the cAMP production induced by (-)-isoprenaline or norepinephrine (NE) in rat brain areas rich in beta 1- or beta 2-adrenoceptors, such as frontal cortex and cerebellum. Moreover, in proliferating brown fat cells, in which the beta 1-adrenoceptor is the only beta-adrenergic subtype coupled to cAMP production, SR 59230A did not modify the production of cAMP induced by NE, whereas CGP 12177 did. In confluent brown fat cells, in which the beta 3-adrenoceptor is the functional beta-adrenergic subtype coupled to adenylyl cyclase, SR 59230A antagonized the NE-induced cAMP accumulation and glycerol release without affecting their basal values, whereas CGP 12177, which per se stimulated cAMP accumulation and glycerol release, did not change the NE-induced increase of either parameter. Finally, SR 59230A concentration-dependently counteracted the NE-stimulated synthesis of uncoupling protein gene in confluent brown fat cells, which is considered mainly a result of selective stimulation of beta 3-adrenoceptors. These results provide evidence that the new selective beta 3-adrenoceptor antagonist can contribute considerably to functional characterization of the beta 3-adrenoceptors.

Actins↗
PubMed1995

Pharmacological antagonism of lipoprivic feeding induced by sodium mercaptoacetate.

Drugs, such as sodium mercaptoacetate and methylpalmoxirate, which block fatty acid oxidation at different levels in the metabolic pathway, stimulate feeding. It is well known that selective centrally induced stimulation of dopamine, serotonin (5-hydroxytryptamine, 5-HT) and beta-adrenoceptors, or inhibition of the opiatergic system substantially decrease food intake in rats trained to eat 4 h a day. The results of the present study show that centrally acting dopaminergic and serotoninergic anorectic drugs, the opiate receptor antagonist naloxone, the alpha-adrenoceptor blocking drug phentolamine, and peripherally administered 5-HT counteract the overeating induced by mercaptoacetate. Comparing these effects to those described in 2-deoxy-D-glucose- and insulin-induced feeding, our data support the proposition that distinct neural circuits are involved in the hyperphagic responses to diverse metabolic stimuli.

Animals↗
PubMed1995

Rat frontal cortex beta 1-adrenoceptors are activated by the beta 3-adrenoceptor agonists SR 58611A and SR 58878A but not by BRL 37344 or ICI 215,001.

SR 58611A, a selective agonist of gut and brown adipose tissue beta 3-adrenoceptors (beta 3 ARs), has been reported to have antidepressant-like activity in rodents, by indicating brain beta 3ARs as the sites of this property. SR 58611A and its acid metabolite SR 58878A, as opposed to BRL 37344, ICI 215,001, and CGP 12177, increased cyclic AMP levels in rat frontal cortex. ICI 215,001, differently from BRL 37344, at concentrations in the millimolar range antagonized norepinephrine- or (-)-isoproterenol-stimulated adenylyl cyclase partially. The increase of cyclic AMP levels induced by SR 58878A was blocked selectively by beta 1AR antagonist CGP 20712A but not by beta 2AR antagonist ICI 118,551. In addition, PCR analysis did not reveal beta 3AR mRNA, and no specific beta 3AR binding sites were detected by [3H]CGP 12177 in rat frontal cortex. When down-regulation of the beta 1AR ligand binding and mRNA levels had been induced in frontal cortex by chronic administration of imipramine, SR 58878A as well as norepinephrine and (-)-isoproterenol inceased the cyclic AMP production less markedly. Our findings indicate that beta 3ARs are absent in the adult rat frontal cortex, and that various beta 3AR agonists differently affect the frontal cortex beta 1ARs, indicating that SR 58611A may exert its putative antidepressant effect acting on the frontal cortex beta 1ARS.

Adipose Tissue, Brown↗
PubMed1994

SR 58611A: a novel thermogenic beta-adrenoceptor agonist.

N(2S)-7-carbethoxymethoxy-1,2,3,4-tetrahydronaphth-2-yl]-(2R )-2-hydroxy-2-(3-chlorophenyl)ethanamine hydrochloride (SR 58611A) increased cyclic AMP levels in membrane homogenates from rat interscapular brown adipose tissue with an EC50 of 20 +/- 2 nM. Substitution of GTP with the GDP analog, guanosine-5'-O[thiodiphosphate], in the incubation medium suppressed the stimulation of adenylyl cyclase activity by SR 58611A. This compound also stimulated glycerol release from the brown fat cells, with an EC50 of 11 +/- 0.4 nM. Only at doses higher than 10 microM did the non-selective beta-adrenoceptor antagonists, propranolol and alprenolol, as well as the selective beta 1- and beta 2-adrenoceptor antagonists, (+-)-[2-(3-carbamoyl-4-hydroxy-phenoxy)- ethylamino]-3-[4(1-methyl-4-trifluoromethyl-2-imidazolyl)-phenoxy]-2 propanol (CGP 20712A) and erythro-(+-)-1-(7-methylindan-4-yloxy)-3-iso-propylamino butan-2-ol-hydrochloride (ICI 118,551), antagonize the SR 58611A-induced stimulation of both adenylyl cyclase activity and lipid metabolism. Since, at high doses, all these beta-adrenoceptor antagonists lack selectivity for beta 1- or beta 2-adrenoceptors, these results suggest that the beta-adrenoceptor agonist, SR 58611A, activates thermogenesis by acting on brown fat cell beta 3-adrenoceptors. This implies that this compound might be useful for treatment of obesity.

Adenylyl Cyclases↗
PubMed1994

A weighty problem.

Explore the source record for details and available documents.

Adipose Tissue, Brown↗
PubMed1993

Neurochemical and behavioral evidence that Ro 41-9067 is a selective presynaptic dopamine receptor agonist.

(-)-2,3,4a,5,6,10b-Hexahydro-7-hydroxy-2-methylbenzo(f)-quinoline 4(1H)-ethanol (Ro 41-9067) was compared with apomorphine, 2-amino-6-allyl-5,6,7,8-tetrahydro-4H-thiazolo-[4,5-d]-azepine (B-HT 920), lisuride and other dopamine (DA) receptor agonists in a series of tests designed to characterize its pharmacological activity on DA receptors. In vitro binding studies indicated that Ro 41-9067 bound selectively to DA D2 vs. D1 receptors. It also had a moderate affinity for serotonin1A and alpha-2 adrenergic receptors. Ro 41-9067 exhibited a marked agonistic component for the presynaptic DA autoreceptors. Indeed, it caused a dose-related reduction in locomotor activity over a wide dose range and prolonged periods of observation without stimulating locomotor activity, reflecting postsynaptic DA receptor activation, even at the highest doses. Ro 41-9067 inhibited the gamma-butyrolactone-induced increase in I-dopa accumulation in the rat striatum, an effect sensitive to haloperiodol. Ro 41-9067 inhibited K(+)-induced [3H]DA release and significantly reduced the striatal contents of the DA metabolites, dihydroxyphenilacetic acid and homovanillic acid. Furthermore, the compound counteracted stereotyped behavior and locomotor stimulation induced by amphetamine. Finally, Ro 41-9067 did not appear to act on postsynaptic D2 receptors because it, similarly to B-HT 920 but differently from bromocriptine, quinpirole and lisuride, did not change basal or forskolin-stimulated adenylate cyclase activity. Only at very high concentrations Ro 41-9067 increased adenylate cyclase activity, this effect being due to a D1 agonistic component.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Butyrolactone↗
PubMed1992

Tolerance to hypoactivity and sensitization to hyperactivity after chronic treatment with a presynaptic dose of lisuride in rats.

We studied the adaptive changes of the locomotor effects of lisuride, a selective agonist for dopamine (DA) D2 receptors, and the functional state of D1 and D2 receptors after repeated administration of lisuride at a dose supposed to act preferentially on DA autoreceptors. Rats were treated daily with saline or lisuride, at a dose that causes a significant reduction in locomotor activity when given to naive rats (25 micrograms/kg i.p.), for 33 days and the effect of different challenging doses of the drug on locomotor activity was measured at different times during and after the treatment. The functional state of D1 and D2 DA receptors was evaluated by measuring SKF 82526-stimulated and LY 171555-inhibited adenylate cyclase (AC) activity in the caudatus/putamen, nucleus accumbens and substantia nigra and naive and chronically treated rats. There was a progressive decline in the ability of lisuride to decrease locomotor activity in rats given daily injections of lisuride, and there was a marked reduction in the threshold dose of lisuride for causing hypermotility. The functional state of DA receptors, positively or negatively linked to AC activity, was not modified by the treatment. The most suitable explanation of the reported adaptive behavioral changes is a down-regulation of DA autoreceptors after chronic treatment with presynaptic doses of lisuride.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1992

Biochemical and functional identification of a novel dopamine receptor subtype in rat brown adipose tissue. Its role in modulating sympathetic stimulation-induced thermogenesis.

Various dopamine (DA) agonists including propylnorapomorphine, lisuride, bromocriptine, apomorphine and quinpirole were found to reduce adenylate cyclase activity in rat brown adipose tissue homogenates. These inhibitory effects were antagonized, with a very low stereoselectivity, by DA receptor antagonists with the following rank order of potency: haloperidol > (+)-butaclamol > or = (-)-butaclamol >> clozapine > or = (-)-sulpiride > or = (+)-sulpiride > or = eticlopride, but not by the alpha-2 adrenoceptor antagonists, phenoxybenzamine and yohimbine or the serotonin receptor antagonists, ketanserin and metergoline. The selective D1 agonist, fenoldopam, was completely inactive in modifying the basal enzyme activity. DA as well as various DA agonists (lisuride > propylnorapomorphine > bromocriptine > apomorphine > quinpirole) dose-dependently reduced the stimulation of adenylate cyclase activity induced either by forskolin or by the beta adrenoceptor agonist, (-)-isoproterenol. Similar results were obtained also in dispersed brown adipocytes. We also found that DA and various DA receptor agonists induced a significant decrease of beta adrenoceptor-stimulated glycerol and nonesterified fatty acids release from brown adipocytes. This effect was selectively antagonized by haloperidol and butaclamol. Thus, the receptors present on the BAT membranes appear to be dopaminergic in nature although they differ from the classical D2 receptor for the following: 1) the low affinity for the most selective D2, D3 and D4 receptor agonist and antagonist (quinpirole, sulpiride and clozapine); 2) the absence of stereoselectivity for various DA antagonists (butaclamol and sulpiride); and 3) the lack of detectable mRNA encoding D2 or D3 DA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1991

Characterization of monoaminergic receptors in hypothalamic nuclei mediating feeding behavior in rats.

It has been proposed that receptors mediating the action of dopamine (DA), serotonin and norepinephrine exist in the hypothalamus to control feeding behavior in the rat. To further characterize the receptor subtypes involved in this phenomenon and determine their locus within specific hypothalamic nuclei, measurements of adenylate cyclase (AC) activity, as a biochemical index of monoaminergic receptors, were taken after administration of various monoaminergic agonists and antagonists. It was first found that DA and selective D2 agonists, such as quinpirole and lisuride, strongly reduced AC activity in homogenates from the lateral perifornical hypothalamus (PFH), where previous evidence has shown DA agonists to inhibit feeding. These inhibitory effects were stereospecifically antagonized by the D2 antagonist (-)-sulpiride. The selective D1 agonist SKF 82526, up to 100 microM, was completely inactive in modifying the basal enzyme function in PFH. In homogenates from rat paraventricular nucleus (PVN), DA (100 microM), quinpirole (10 microM) and SKF 82526 (100 microM) were unable to affect AC activity, consistent with previous pharmacological evidence showing DA in the PVN to have no effect on feeding. These results suggest the presence of D2 receptors in the PFH but not in the PVN and the absence of D1 receptors in both areas. Under the same experimental conditions, the alpha 2 adrenoceptor agonist clonidine was able to inhibit AC in the PVN, and this effect was reversed by the alpha adrenoceptor antagonist phenoxybenzamine. These results supported the previously described PVN alpha 2 adrenergic system.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1990

Repeated administration of lisuride down-regulates dopamine D-2 receptor function in mesostriatal and in mesolimbocortical rat brain regions.

Functional modifications of both D-1 and D-2 dopamine (DA) receptor subtypes following repeated administration of lisuride, a DA agonist that acts selectively on D-2 DA receptors were studied. The functional state of D-1 and D-2 DA receptors was evaluated from measurements of SKF 82526-stimulated and bromocriptine-inhibited adenylate cyclase activity in different brain regions of rats treated daily for 26 days with saline or lisuride (100 micrograms/kg i.p.). Persistent stimulation by lisuride of DA receptors in striatum, nucleus accumbens, substantia nigra, frontal cortex, hippocampus and pituitary gland induced a down-regulation of D-2 receptors without changing the functional activity of D-1 receptors.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗