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Biomedical subjects

H A Navarro

Publications and source records attributed to H A Navarro.

At least 19 recordsLinked to original sources
PubMed2002

In vitro and in vivo characterization of [125I]iodomethyllycaconitine in the rat.

The in vitro and in vivo binding characteristics of [125I]iodomethyllycaconitine ([125I]iodoMLA) were determined in the rat. [125I]iodoMLA binding to rat cerebral cortex membranes was saturable and reversible and its specific binding represented approximately 70-80% of the total binding. [125I]iodoMLA labeled a single site with Kd = 1.8 +/- 0.4 nM and Bmax = 68 +/- 3 fmol/mg protein. Kinetic analysis revealed a t1/2 for association and dissociation of 10.5 +/- 3.1 and 10.3 +/- 1.6 min, respectively. Pharmacological characterization of [125I]iodoMLA binding indicated that it was specific for the alpha7 nAChR. In vitro brain region binding studies revealed greater binding in regions known to contain high numbers of alpha7 nAChRs. The analysis of the biodistribution of intravenously administered [125I]iodoMLA indicated that it was rapidly cleared and exhibited poor brain penetration; nevertheless, the levels of [125I]iodoMLA in alpha7 nAChR-rich target regions were significantly increased compared to the nontarget region (cerebellum) 60-120 min after administration. No metabolism of MLA by human liver S9 fraction was detected. Our results suggest that [125I]iodoMLA will be a useful radioligand to study the alpha7 nAChR in vitro and in vivo.

Animals↗
PubMed2001

Synthesis, nicotinic acetylcholine receptor binding, and antinociceptive properties of 2-exo-2-(2'-substituted-3'-phenyl-5'-pyridinyl)-7-azabicyclo[2.2.1]heptanes. Novel nicotinic antagonist.

A series of 2'-substituted-3'-phenyl epibatidine analogues were synthesized and evaluated for inhibition of binding at nicotine acetylcholine receptors and for antinociceptive properties in mice. The introduction of a bulky phenyl group at the 3'-position exerted a profound influence on both receptor binding and antinociceptive effects. Substitution of different groups at the 2'-position distinguished between agonist and antagonist properties. These results demonstrate that structural requirements for receptor activities and recognition are distinctively different.

Analgesics↗
PubMed2001

Neonatal chlorpyrifos administration elicits deficits in immune function in adulthood: a neural effect?

Neural input plays a key role in the establishment of immune function, and environmental agents or drugs that interfere with the development of the nervous system elicit corresponding immunologic deficits. In the current study, we gave neonatal rats the widely used organophosphate pesticide, chlorpyrifos (CPF), and determined the immediate and long-term effects on T-lymphocyte function. Exposure of neonatal rats to 1 mg/kg of CPF daily on postnatal days (PN) 1-4 had no immediate effect (PN5) on T-cell mitogenic responses to concanavalin A challenge. However, once the animals reached adulthood, T-cell responses were significantly impaired. There were no deficits in basal T-cell replication rates, implying that the adverse effect of CPF exposure was specific to mitogenic activation. Treatment during a later neonatal period (PN11-14) elicited similar deficits in adulthood. CPF administration leads to inhibition of cholinesterase, and a cholinergic connection is supported by the fact that the results seen here correspond to those seen with a direct cholinergic stimulant (nicotine) administered during gestation or adolescence. These results indicate that exposure to CPF during a developmental period in which this organophosphate pesticide is known to produce lasting changes in neural function, elicits corresponding, long-term deficits in immune competence.

Age Factors↗
PubMed2001

Adolescent nicotine: deficits in immune function.

Maternal cigarette smoking during pregnancy is known to alter immune function in the offspring and recent studies with animals indicate that prenatal nicotine exposure leads to lasting deficiencies in T-lymphocyte mitogenic responses, likely through excessive cholinergic stimulation during a critical stage of development. The current study was conducted to determine if the vulnerable period for nicotine-induced mis-programming of immune responses extends into adolescence, the stage at which most smokers begin tobacco use. Adolescent rats were given nicotine via osmotic minipump infusions on postnatal days (PN) 30-47.5, using a regimen that produces plasma levels (25 ng/ml) of nicotine similar to those in smokers or in users of transdermal nicotine patches. Toward the end of the infusion period (PN45) and 1 month after termination of nicotine exposure (PN80), we examined the mitogenic responses of splenocytes to Concanavalin A. Although no deficiencies were seen on PN45, there were robust decreases in mitogenic responses on PN80, with deficits apparent at both suboptimal and optimal concentrations of Concanavalin A. These results indicate that the adolescent immune system is vulnerable to nicotine-induced disruption of T-cell function.

Age Factors↗
PubMed2001

[(125)I]3beta-(4-ethyl-3-iodophenyl)nortropane-2beta-carboxylic acid methyl ester ([(125)I]EINT): a potent and selective radioligand for the brain serotonin transporter.

The binding characteristics of [(125)I]3beta-(4-ethyl-3-iodophenyl)nortropane-2beta-carboxylic acid methyl ester ([(125)I]EINT), a high-affinity selective ligand for the serotonin transporter (5-HTT), and its binding characteristics to rat brain membranes were determined. [(125)I]EINT binding to rat cerebral cortex membranes was saturable and reversible, and its specific binding represented approximately 90% of the total binding. [(125)I]EINT labeled a single site with K(d) = 0.22 +/- 0.03 nM and B(max) = 583 +/- 38 fmol/mg protein. Kinetic analysis revealed a t(1/2) for association and dissociation of 20 and 24 min, respectively. Pharmacological characterization of [(125)I]EINT confirmed its high specificity for the 5-HTT. The pattern of brain region distribution in vivo of intravenously administered [(125)I]EINT indicated greater accumulation of the radioligand in 5-HTT-rich brain regions. However, the signal-to-background ratio was low. Thus, [(125)I]EINT appears to be a useful radioligand for studying the 5-HTT in vitro, but it may not be a good in vivo ligand.

Animals↗
PubMed2001

Synthesis, nicotinic acetylcholine receptor binding, and antinociceptive properties of 2-exo-2-(2'-substituted 5'-pyridinyl)-7-azabicyclo[2.2.1]heptanes. Epibatidine analogues.

A convenient, high-yield synthesis of 7-tert-butoxycarbonyl-7-azabicyclo[2.2.1]hept-2-ene (5), which involved the addition of tributyltin hydride to 7-tert-butoxycarbonyl-2-p-toluenesulfonyl-7-azabicyclo[2.2.1]hept-2-ene (4) followed by elimination of the tributyltin and p-tolylsulfonyl groups using tetrabutylammonium fluoride was developed. The addition of 2-amino-5-iodopyridine to 5 under reductive Heck conditions provided 7-tert-butoxycarbonyl-2-exo-(2'-amino-5'-pyridinyl)-7-azabicyclo[2.2.1]heptane (6). Compound 6 was the key intermediate used to prepare epibatidine analogues where the 2'-chloro group on the pyridine ring was replaced with a fluorine (1b), bromine (1c), iodine (1d), hydroxy (1e), amino (1f), dimethylamino (1g), trifluoromethanesulfonate (1h), and hydrogen (1i) group. (+)- and (-)-Epibatidine and compounds 1b-d and 1i all possess similar binding affinities at the alpha(4)beta(2) nAChR receptors labeled by [(3)H]epibatidine. Compound 1f has affinity similar to nicotine, whereas compounds 1e, 1g, and 1h have much lower affinity. The binding affinity appears to be dependent upon the electronic nature of the substituent. However, other factors are also involved. None of the compounds possesses appreciable affinity for the alpha(7) nAChR labeled by [(125)I]iodo-MLA. With the exception of 1f and 1g, all the epibatidine analogues are full agonists (tail flick test) in producing antinociception after intrathecal injection in mice.

Analgesics, Non-Narcotic↗
PubMed2001

Bioactive constituents of the roots of Licania intrapetiolaris.

Fractionation of a methanol extract of the roots of Licania intrapetiolaris, as directed by activity against the KB assay, has led to the isolation of two novel clerodane diterpenoids, intrapetacins A (1) and B (2), and the known triterpenoid cucurbitacin B (3). The structures of 1 and 2 were deduced from one- and two-dimensional NMR experiments, including relative stereochemical assignments based on NOESY correlations and COSY coupling constants. Compound 3 was the most potent against the KB assay, but both 1 and 2 displayed moderate cytotoxicity. When evaluated against an antifungal assay using Aspergillus niger, 2 caused a significant zone of inhibition of fungal growth, while 1 was completely inactive. To the best of our knowledge, this is the first report of the isolation of bioactive compounds from the genus Licania.

Aspergillus niger↗
PubMed2001

Macharistol, a new cytotoxic cinnamylphenol from the stems of Machaerium aristulatum.

A new cinnamylphenol, macharistol (1), along with a known pterocarpan, (+)-medicarpin (2), were isolated as cytotoxic constituents from the stems of Machaerium aristulatum. In addition, a known pterocarpan, (+)-maackiain (3), and a known isoflavone, formononetin (4), were identified as inactive constituents. Compound 1 was evaluated in the in vivo hollow fiber assay with KB, Col-2, and hTERT-RPE1 cells and found to be inactive at the highest dose (25 mg/kg body weight) tested.

Antineoplastic Agents, Phytogenic↗
PubMed2000

Gestational nicotine exposure alone or in combination with ethanol down-modulates offspring immune function.

Prenatal nicotine exposure has been shown to disrupt the development of a number of peripheral organs. In the current study, we examined the effects of gestational nicotine exposure, alone or in combination with ethanol exposure, on offspring immune function. Timed pregnant rats were treated with either nicotine (6 mg/kg/day) from gestation day 4-20 using subcutaneously implanted osmotic mini-pumps or ethanol administered in the drinking water (15% w/v) from gestation day 10-20. The combined exposure group received both treatments. The ability of offspring T and B cells to proliferate in response to nonspecific stimulation by Concanavalin A or lipopolysaccharide, respectively, was determined on postnatal days 9, 15, 22, 29, 64, and 86. Offspring splenocyte beta(2)-adrenoceptor binding was also measured. Nicotine or nicotine+ethanol suppressed splenocyte responsiveness to Concanavalin A or lipopolysaccharide which was similar in timing and magnitude to that seen with ethanol alone. Splenocytes from these groups remained subresponsive to stimulation well into adulthood. The combined drug treatment caused an overall reduction in spleen beta-adrenergic receptor binding whereas the individual drug treatments did not alter the development of spleen beta-adrenergic receptors.Our results indicate that prenatal nicotine exposure can cause long-term suppression of the proliferative response of offspring immune cells. Moreover, the effects of nicotine+ethanol may cause more severe deficits in adulthood.

Animals↗
PubMed1991

Prenatal terbutaline treatment: tissue-selective dissociation of perinatal changes in beta-adrenergic receptor binding from regulation of adenylate cyclase activity.

The role of prenatal beta-receptor stimulation in development of adrenergic reactivity was examined by administering the beta-agonist, terbutaline, to pregnant rats on gestational days 17, 18 and 19. On gestational day 20, liver membrane beta-receptor binding capabilities showed the depression characteristic of down-regulation, but heart and kidney receptor binding were essentially normal. Basal adenylate cyclase activity in the fetal liver membrane preparation was unchanged by terbutaline exposure and enzymatic reactivity to beta-adrenergic stimulation showed only a slight lowering; forskolin stimulation, however, was markedly increased in the terbutaline group. By postnatal day 2, receptor binding had returned to normal in the liver and remained at control levels in the other two tissues. Responsivity of adenylate cyclase to beta-receptor stimulation was markedly elevated in heart and kidney membranes; the effect represented an alteration at the level of the cyclase itself, rather than the receptor, since both basal activity and forskolin stimulation of the enzyme showed equivalent enhancement. These data thus suggest that early beta-adrenergic stimulation promotes cellular reactivity by fostering the development of membrane transduction mechanisms, rather than through effects on the receptor ligand binding site per se.

Adenylyl Cyclases↗
PubMed1991

Control of adenylate cyclase activity in developing rat heart and liver: effects of prenatal exposure to terbutaline or dexamethasone.

Adrenergic stimulation and glucocorticoids have been hypothesized to control the development of beta-adrenergic receptors and responsiveness. In the current study, rats were exposed to a beta-agonist (terbutaline) or a glucocorticoid (dexamethasone) during late gestation, and the development of adenylate cyclase activity and beta-receptor binding was evaluated in membranes prepared from the heart and liver. In control heart, basal, isoproterenol-stimulated and forskolin-stimulated adenylate cyclase showed distinct developmental spikes of activity that were unrelated to changes in receptor binding sites, but that instead corresponded temporally to periods of sympathetic neuronal activation. Prenatal exposure to terbutaline initially enhanced all three enzymatic measures in the immediate postpartum period but delayed the appearance and exaggerated the magnitude of the subsequent peaks; again, these changes occurred without specific relation to effects on receptor binding. Dexamethasone produced a similar shift in the peaks of cardiac enzyme activity. In the liver, where beta-adrenergic receptors and responsiveness decline after birth, terbutaline and dexamethasone had much smaller effects on adenylate cyclase. These results suggest that beta-adrenergic stimulation serves as a trophic factor controlling the ontogenetic rise of adenylate cyclase activity; regulation involves the level of the enzyme itself rather than changes in receptor binding capabilities or receptor-specific linkages. Consequently, prenatal administration of beta-agonists or glucocorticoids can cause long-term alterations in enzyme activity and responsiveness.

Adenylyl Cyclases↗
PubMed1990

Fetal nicotine exposure produces postnatal up-regulation of adenylate cyclase activity in peripheral tissues.

Gestational exposure to nicotine has been shown to affect development of noradrenergic activity in both the central and peripheral nervous systems. In the current study, pregnant rats received nicotine infusions of 6 mg/kg/day throughout gestation, administered by osmotic minipump implants. After birth, offspring of the nicotine-infused dams exhibited marked increases in basal adenylate cyclase activity in membranes prepared from kidney and heart, as well as supersensitivity to stimulation by either a beta-adrenergic agonist, isoproterenol, or by forskolin. The altered responses were not accompanied by up-regulation of beta-adrenergic receptors: in fact, [125I]pindolol binding was significantly decreased in the nicotine group. These results indicate that fetal nicotine exposure affects enzymes involved in membrane receptor signal transduction, leading to altered responsiveness independently of changes at the receptor level.

Adenylyl Cyclases↗
PubMed1990

Prenatal nicotine exposure impairs beta-adrenergic function: persistent chronotropic subsensitivity despite recovery from deficits in receptor binding.

Gestational exposure to nicotine has been shown to interfere with biochemical markers of development of central and peripheral noradrenergic activity. The current study examines the development and function of cardiac beta-adrenergic receptors in the offspring of pregnant rats given nicotine infusions of 6 mg/kg/day from gestational days 4 through 20, administered by subcutaneously implanted osmotic minipumps. Prenatal nicotine exposure delayed the development of beta-adrenergic receptor binding capabilities, as assessed with [125I]pindolol in membrane preparations from heart and kidney. The deficits in receptor binding were associated with marked subsensitivity of chronotropic responses to administration of a beta-adrenergic agonist, isoproterenol. Although the effects on receptor binding resolved after weaning, functional deficiencies in responsiveness to isoproterenol or to preganglionic electrical stimulation of sympathetic nerves to the heart persisted into adulthood. These results indicate that prenatal exposure to nicotine produces long-term alterations in adrenergic responsiveness of sympathetic target tissues.

Aging↗
PubMed1990

Regulation of beta-adrenergic receptor-mediated processes in fetal rat lung: selective desensitization caused by chronic terbutaline exposure.

Fetal lung beta-receptors become effectively coupled to lung fluid reabsorption and enzymes involved in surfactant synthesis on the day before birth, a period when circulating catecholamine levels are high. Accordingly, we examined the effects of repeated maternal terbutaline exposure on beta-receptor binding capabilities and beta-receptor-mediated processes in the fetal rat lung. Administration of terbutaline to pregnant rats on gestational day 17-20 produced significant reductions in beta-receptor binding to membrane preparations. Similarly, beta-receptor-mediated stimulation of adenylate cyclase activity and ornithine decarboxylase activity showed marked desensitization in the terbutaline-exposed fetuses. However, the linkage of beta-receptors to lung fluid reabsorption and phosphatidic acid phosphatase, an enzyme involved in surfactant synthesis, did not desensitize with chronic terbutaline pretreatment; both of these processes displayed the normal onset of responsiveness on gestational day 21 in the treated animals, as well as a normal magnitude of response. Hence, beta-receptor-mediated events in the developing lung may be differentially regulated during exposure to agonists, allowing the selective expression or depression of function when circulating catecholamine levels are high.

Absorption↗
PubMed1990

Regulation of postnatal beta-adrenergic receptor/adenylate cyclase development by prenatal agonist stimulation and steroids: alterations in rat kidney and lung after exposure to terbutaline or dexamethasone.

Glucorticoids and adrenergic stimulation are both thought to control the development of beta-adrenergic receptors/responses. In the current study, rats were exposed to dexamethasone or terbutaline during late gestation and the development of beta-receptor binding capabilities and adenylate cyclase activity evaluated in membrane preparations from kidney and lung. Prenatal dexamethasone exposure produced postnatal adrenergic hyperreactivity of kidney adenylate cyclase; the effect resulted from increases in the enzyme itself, as both basal adenylate cyclase and forskolin-stimulation of the enzyme were also increased by dexamethasone. Similarly, prenatal terbutaline exposure evoked increases in basal, isoproterenol-stimulated and forskolin-stimulated adenylate cyclase in the kidney. In the lung, dexamethasone produced an initial postnatal deficit in basal adenylate cyclase and deficient responsiveness to isoproterenol, but the deficit resolved shortly after birth. Terbutaline selectively promoted the ability of isoproterenol to stimulate lung adenylate cyclase in the first few days after birth, without alterations in basal adenylate cyclase; this was followed by a period of prolonged subsensitivity of both basal and isoproterenol-stimulated activity. Although dexamethasone and terbutaline also caused significant changes in development of beta-receptor binding capabilities, in neither tissue could these effects account for the direction or magnitude of the changes in adenylate cyclase reactivity. Thus, glucocorticoids and beta-agonists can participate in the programming of development of postsynaptic reactivity by exerting actions upon post-receptor coupling mechanisms.

Adenylyl Cyclases↗
PubMed1990

Prenatal exposure to propranolol via continuous maternal infusion: effects on physiological and biochemical processes mediated by beta adrenergic receptors in fetal and neonatal rat lung.

During lung development, beta adrenergic receptors undergo transient coupling to enzymes and physiological processes which govern respiratory function and trophic responses to neural stimulation. To determine the role of endogenous catecholamines in mediating these processes, we examined the gestational and postnatal effects of chronic propranolol infusion (10 mg/kg/day) throughout fetal development. The effectiveness of receptor blockade in dam and fetus were confirmed through measurements of heart rate and enzymatic stimulatory responses to acute challenge with beta agonists (terbutaline to isoproterenol). Propranolol antagonized the ability of terbutaline to stimulate fetal lung fluid resorption and phosphatidic acid phosphatase, a key enzyme in surfactant synthesis. After birth, basal lung compliance and the compliance response to beta adrenergic stimulation were compromised in the neonates that had been exposed to propranolol before birth, despite the fact that direct receptor antagonism had disappeared by that time. After weaning, animals exposed to prenatal propranolol showed interference with basal activity of ornithine decarboxylase (an enzyme involved in transduction of neuronal and hormonal trophic stimuli) and its response to acute beta adrenergic challenge. These results suggest that endogenous fetal catecholamines participate in perinatal respiratory adaptation to air-breathing and help to program future cellular responsiveness to neuronal input.

Animals↗