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D J Reis

Publications and source records attributed to D J Reis.

At least 19 recordsLinked to original sources
PubMed1992

Action of externally applied ATP on rat reticulospinal vasomotor neurons.

In anesthetized rats, iontophoretic application of ATP excited the spinal cord-projection neurons in the rostral ventrolateral reticular nucleus of the medulla oblongata. The neuronal response to ATP was mimicked and then blocked by alpha,beta-methylene-ATP, a metabolically stable ATP analogue, and the response was abolished by suramin. Microinjections of ATP (3-100 pmol) into the rostral ventrolateral medulla produced a powerful pressor response. The results suggest that ATP may function as a neurotransmitter or neuromodulator involved in medullary regulation of cardiovascular functions.

Adenosine Triphosphate↗
PubMed1992

Induction of calcium-independent nitric oxide synthase activity in primary rat glial cultures.

Exposure of primary cultures of neonatal rat cortical astrocytes to bacterial lipopolysaccharide (LPS) results in the appearance of nitric oxide synthase (NOS) activity. The induction of NOS, which is blocked by actinomycin D, is directly related to the duration of exposure and dose of LPS, and a 2-hr pulse can induce enzyme activity. Cytosol from LPS-treated astrocyte cultures, but not from control cultures, produces a Ca(2+)-independent conversion of L-arginine to L-citrulline that can be completely blocked by the specific NOS inhibitor NG-monomethyl-L-arginine. The induced NOS activity exhibits an apparent Km of 16.5 microM for L-arginine and is dependent on NADPH, FAD, and tetrahydrobiopterin. LPS also induces NOS in C6 glioma cells and microglial cultures but not in cultured cortical neurons. The expression of NOS in astrocytes and microglial cells has been confirmed by immunocytochemical staining using an antibody to the inducible NOS of mouse macrophages and by histochemical staining for NADPH diaphorase activity. We conclude that glial cells of the central nervous system can express an inducible form of NOS similar to the inducible NOS of macrophages. Inducible NOS in glia may, by generating nitric oxide, contribute to the neuronal damage associated with cerebral ischemia and/or demyelinating diseases.

Amino Acid Oxidoreductases↗
PubMed1992

A novel inositol phosphate selectively inhibits vasoconstriction evoked by the sympathetic co-transmitters neuropeptide Y (NPY) and adenosine triphosphate (ATP).

Postganglionic sympathetic nerves release norepinephrine (NE) as their primary neurotransmitter at vascular and other targets. However, much evidence supports involvement of additional messengers, co-transmitters, which are co-released with NE upon sympathetic nerve stimulation and thereby contribute to their actions, e.g., vasoconstriction. Two such putative co-transmitters, neuropeptide Y (NPY) and adenosine triphosphate (ATP) have been of particular interest since they fulfill several neurotransmitter criteria. Importantly, hitherto it has been difficult to antagonize vasoconstriction evoked by either NPY or ATP with agents that are devoid of intrinsic activity. The present study describes the ability of a novel inositol phosphate, D-myo-inositol 1,2,6-trisphosphate (Ins[1,2,6]P3; PP-56) to in vitro potently block vasoconstrictor responses elicited by NPY and ATP, but not by NE, as studied in guinea-pig isolated basilar artery. The action of Ins[1,2,6]P3 does not seem to occur through antagonism at NPY- or ATP-receptor recognition sites, labeled by 125I-peptide YY and 35S-gamma-ATP, respectively, in membranes of rat cultured vena cava vascular smooth muscle cells. However, it does involve inhibition of the influx of Ca2+ induced by either co-transmitter in these same vena cava cells. It is proposed that Ins[1,2,6]P3 may be a useful functional antagonist of non-adrenergic component(s) of the vasoconstrictor response to sympathetic nerve stimulation.

Adenosine Triphosphate↗
PubMed1992

Evidence for a bioactive clonidine-displacing substance in peripheral tissues and serum.

Clonidine-displacing substance (CDS) from brain is biologically active in the kidney and stomach and on platelets. To determine whether CDS is contained in these and other peripheral tissues, homogenates of fresh brain, eight other organs and serum from rat were ultrafiltered (less than 10,000 mol. wt only), dried and extracted with methanol. Evaluation by radioimmunoassay (RIA) using antibodies to p-aminoclonidine showed that adrenal gland and gastric fundus (GF) contained significantly greater amounts of CDS-like radioimmunoactivity than brain; intermediate-to-low activity was present in heart, small intestine, serum, kidney and liver; lung and skeletal muscle values were near-background. RIA-positive extracts elicited well-correlated contractile activity in a GF smooth muscle bioassay; contractions persisted in the presence of antagonists of various transmitters and modulators, but were abolished by low concentrations of the calcium channel blocker verapamil. Serum levels of CDS were profoundly reduced following removal of the adrenal glands. We conclude that a CDS-like substance is present not only in brain as previously reported, but also in peripheral organs and in the circulation.

Adrenal Glands↗
PubMed1992

Lesions of nigrostriatal pathway reduce expression of tyrosine hydroxylase gene in residual dopaminergic neurons of substantia nigra.

The effects of unilateral mechanical transection of the nigrostriatal bundle of rat brain on the level of tyrosine hydroxylase (TH) mRNA and on the activity of TH enzyme in the substantia nigra (SN) were examined. Lesions resulted, by 14 days, in reductions of TH mRNA level to 10% of control and of TH enzyme activity to 39% of control in the ipsilateral SN. The percentage of TH mRNA is lower than either the percentage of surviving dopaminergic neurons or the remaining TH enzyme activity. In situ hybridization analyses also demonstrated the reduction of TH mRNA concentration in surviving dopaminergic neurons in the ipsilateral SN.

Animals↗
PubMed1992

Inositol hexakisphosphate excites rat medullary sympathoexcitatory neurons in vivo.

Inositol hexakisphosphate (IP6) was microinjected into the rostral ventrolateral reticular nucleus or iontophoresed onto reticulospinal sympathoexcitatory neurons of the nucleus in anesthetized rats. IP6 (5-500 pmol) induced a dose-dependent potent and prolonged elevation of arterial pressure which was mimicked by microinjection of ethyleneglycol-bis (beta-aminoethylether)N,N,N',N'-tetraacetic acid (EGTA), while myo-inositol was ineffective. Iontophoretic application of IP6 and EGTA excited the medullary sympathoexcitatory neurons but myo-inositol had no effect. The effect of IP6 on firing rate of the sympathoexcitatory neurons was abolished by co-administration of Ca2+ ions onto these neurons. The results indicate that IP6 acts extracellularly to excite the medullary sympathoexcitatory neurons. The excitatory actions of IP6 may depend, at least in part, on a calcium-chelating action. Chelation of extracellular Ca2+ might be a physiological action of IP6.

Animals↗
PubMed1992

Effects of systemic ethanol on medullary vasomotor neurons and baroreflexes.

The acute effects of systemic ethanol on reticulospinal sympathoexcitatory neurons were examined in vivo in anesthetized, paralyzed rats. Ethanol (0.45 g/kg, i.v.) potentiated the depressant effect of locally applied gamma-aminobutyric acid (GABA) but attenuated the excitatory effect of L-glutamate. The baroreflex-mediated inhibition of these neurons and sympathetic nerve activity were partially depressed by the agent while aortic nerve activity and its sensitivity to changes in arterial pressure were not altered. These results suggest that systemic ethanol may markedly influence cardiovascular function by interfering in medullary GABAergic and glutamatergic transmissions involved in central control of the cardiovascular system.

Animals↗
PubMed1992

Specific binding of inositol hexakisphosphate (phytic acid) to adrenal chromaffin cell membranes and effects on calcium-dependent catecholamine release.

In a membrane preparation of cultured bovine adrenal chromaffin cells, [3H]inositol hexakisphosphate ([3H]InsP6) was shown to bind specifically with a Kd of 90 nM and a Bmax of 700 fmol/mg protein. The Hill coefficient was not significantly different from unity. The association of [3H]InsP6 was slow, with equilibrium binding being reached within 10 min. The dissociation of [3H]InsP6 showed monophasic kinetics. In [3H]InsP6 competition binding experiments, we found that reduction in the number of phosphorylated sites in inositol resulted in a gradual loss of binding potency. In intact bovine adrenal chromaffin cells, InsP6 elicited a concentration-dependent facilitation of 45C2+ influx along with the release of the catecholamines, epinephrine and norepinephrine. The latter responses were slower and longer-lasting than responses to depolarizing stimuli, such as nicotine and high K+. The catecholamine release required the presence of extracellular Ca2+. In good agreement with the binding studies, lower inositol phosphates displayed reduced secretagogue potency. In conclusion, in bovine adrenal chromaffin cells, InsP6 appeared to bind to specific sites and elicited Ca2+ influx and catecholamine release.

Adrenal Glands↗
PubMed1992

Identification of cultured cells selectively expressing Y1-, Y2-, or Y3-type receptors for neuropeptide Y/peptide YY.

Neuropeptide Y (NPY) and peptide YY (PYY) are homologous 36 amino acid amidated peptides that often, but not always, exert similar actions and binding profiles. The present study of cultured cells confirms that both peptides as well as radioiodinated analogs, i.e. 125I-Bolton-Hunter-NPY (125I-BH-NPY) and 125I-peptide YY (125I-PYY), show high affinity to binding sites/receptors of the previously proposed Y1- and Y2-subtypes, selectively expressed by the human neuroblastoma cell lines, SK-N-MC and SK-N-BE(2), respectively. In contrast, bovine adrenal chromaffin cells did not bind 125I-PYY, while displaying high affinity 125I-BH-NPY sites, and may therefore represent a cell type expressing a recently proposed Y3-type of (NPY-preferring) receptors. Several non-labeled fragments/analogs have been used in displacement experiments to further characterize the structural requirements for Y1-, Y2-, and Y3-type binding. In every instance, specific binding was reduced by addition of 5'-guanylylimidodiphosphate [Gpp(NH)p], indicating that the three receptor subtypes belong to the G-protein-coupled superfamily of receptors. Moreover, in both neuroblastoma cell lines, the peptides elicited, with appropriate orders of potency, reduction of forskolin-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) accumulation. Finally, NPY-evoked 45Ca2+ influx was observed in SK-N-MC and in chromaffin cells. A common dual coupling mechanism of NPY/PYY receptors, i.e. to reduction of cAMP and to Ca2+ elevation, is therefore suggested to exist, although both phenomena could not be demonstrated in every cell type.

Animals↗
PubMed1992

Evidence nitric oxide mediates the vasodepressor response to hypoxia in sino-denervated rats.

Systemic hypoxia, produced in deeply anesthetized, paralyzed rats in which arterial chemoreceptors were denervated, elicited a decrease in arterial pressure (AP) averaging -47 mmHg. Systemic administration of NG-nitro-L-arginine (L-NO2Arg), an inhibitor of nitric oxide (NO) synthase, attenuated the hypoxic depressor response by 79% and elevated AP by 21 mmHg. The effects of L-NO2Arg on the hypoxic depressor response and arterial pressure were reversed by systemic administration of L- but not D-arginine. Elevation of AP with arginine-vasopressin or reduction of AP with nitroprusside to the pre-L-NO2Arg levels did not modify the fall of AP to hypoxia. Endogenous NO synthesized in vivo from L-arginine, mediates most of the hypoxic depressor response.

Anesthesia, General↗
PubMed1992

Inhibition of nitric oxide synthesis increases focal ischemic infarction in rat.

We investigated whether inhibition of nitric oxide (NO) biosynthesis with N-omega-nitro-L-arginine (NNA), a competitive inhibitor of NO synthase (NOS), would modify the volume of the focal ischemic infarction produced by occlusion of the middle cerebral artery (MCA) in spontaneously hypertensive rats. NNA was infused for 1 h (2.4 mg/kg/h) immediately following occlusion of the MCA. NNA increased lesion volume 24 h later by 32% over controls (150.8 +/- 16.6 to 199.2 +/- 17.4 mm3; p less than 0.001, n = 6). This effect was antagonized by co-infusion of L- but not D-arginine. The antihypertensive rilmenidine (0.75 mg/kg) reduced the lesion by 27% (p less than 0.05, n = 4). Changes in lesion size were confined to the penumbra. NNA increased arterial pressure (AP) (118 +/- 8.9 to 149 +/- 16.0 mm Hg; p less than 0.01, n = 3) but did not change regional CBF. However, elevation of AP did not change the lesion volume or distribution. We conclude that inhibition of the constitutive form of NOS in vivo increases the volume of focal ischemic infarction as a consequence of reduced NO biosynthesis. The absence of NO availability may extend lesion formation by inhibition of reactive hyperemia, platelet disaggregation, and/or release of neuroprotective neuromodulators in the penumbra, which may counteract and override any of its neurotoxic actions.

Amino Acid Oxidoreductases↗
PubMed1992

Stimulation of Cl area neurons globally increases regional cerebral blood flow but not metabolism.

We examined the effects of electrical and chemical stimulation of the Cl area of the rostral ventrolateral medulla (RVL) on regional cerebral blood flow (rCBF) and regional cerebral glucose utilization (rCGU) in anesthetized (chloralose), paralyzed (curare) and ventilated rats. rCBF and rCGU were measured using 14C-iodoantipyrine (IAP) and 14C-deoxyglucose (2-DG), respectively, as indicators, with bilateral regional dissection of 11 brain regions. Electrical stimulation of the RVL elicited increases in arterial pressure (AP), heart rate (HR) and plasma concentration of epinephrine (EPI) and norepinephrine (NE). In addition, stimulation of the RVL, but not the adjacent medial longitudinal fasciculus, with AP maintained, increased rCBF (p less than 0.05, n = 6), but not rCGU, bilaterally and symmetrically (134-169% of control) throughout the brain. Bilateral adrenalectomy abolished the increase in plasma EPI elicited by stimulation of the RVL but did not affect resting rCBF (n = 5) or the elevation in rCBF elicited by RVL stimulation (n = 5). Increases in rCBF elicited by RVL stimulation were also unaffected by acute transection of the superior cervical ganglion (p greater than 0.05). Kainic acid (KA) microinjected into the RVL unilaterally (n = 6) at a dose producing sustained elevation in AP (5 nmol in 100 nl), elicited changes in rCBF similar to those elicited by electrical stimulation. We conclude that neurons within the RVL, possibly those of the adrenergic Cl group, can initiate a global cerebrovasodilation, but not an increase in rCGU, largely through neural pathways intrinsic to the brain. The responses may represent activation of networks in RVL mediating circulatory adjustments to hypoxia.

Animals↗
PubMed1992

Reduction in focal cerebral ischemia by agents acting at imidazole receptors.

Treatment with the alpha 2-adrenergic antagonist idazoxan (IDA) can provide protection from global cerebral ischemia. However, IDA also recognizes another class of receptors, termed imidazole (IM) receptors, which differ from alpha 2-adrenergic receptors and are responsible for the hypotensive actions of some centrally acting agents such as the oxazole rilmenidine (RIL). We therefore sought to determine whether RIL, an agent highly selective for IM receptors, offered protection from focal cerebral ischemia elicited in rat by ligation of the middle cerebral artery (MCA). We compared the effects of RIL with the effects of IDA and the selective non-IM alpha 2-antagonist SKF 86466 (SKF). In addition, we examined whether the neuroprotective effects of RIL and IDA could be attributed to changes in local CBF (LCBF). The MCA was occluded and animals either received immediate administration of drug while arterial pressure was maintained for 1 h or had local CBF increased to 200% of control for 1 h by hypercapnia or hypertension. RIL elicited a significant dose-dependent preservation of tissue to 33% of control at optimal dose (0.75 mg/kg). IDA (3 mg/kg) significantly reduced the size of ischemic infarction by 22%. In contrast, SKF (15 mg/kg) as well as doubling of LCBF did not preserve ischemic tissue. We conclude that both RIL and IDA can reduce focal ischemic infarction but that the mechanism does not appear secondary to antagonism of alpha 2-adrenergic receptors or elevation of LCBF. Occupation of IM receptors, either in the ischemic zone or at remote brain sites, may be responsible for neuroprotection of RIL and IDA.

Adrenergic alpha-Agonists↗
PubMed1992

Imidazole receptors and clonidine-displacing substance in relationship to control of blood pressure, neuroprotection, and adrenomedullary secretion.

Clonidine, idazoxan, rilmenidine, and comparable agents bind to imidazol(in)e (IR), as well as alpha 2-adrenergic, receptors. Interaction with IRs mediates the hypotension elicited by these drugs at their site of action in the rostral ventrolateral medulla oblongata (RVL) and probably the neuroprotection in focal ischemic cerebral infarction. Unlike alpha 2-adrenergic receptors, IRs are not coupled to G-proteins. Their native ligand may be clonidine-displacing substance (CDS), a potent, partially purified adrenomedullary secretagogue, distributed regionally in brain and some peripheral organs. IRs and CDS may be important in the genesis, expression, and/or therapy of hypertension and stroke.

Adrenal Medulla↗
PubMed1992

Cyanide excites medullary sympathoexcitatory neurons in rats.

Microinjections of cyanide (300 pmol) into the cardiovascular portion of the rostral ventrolateral reticular nucleus (RVL) of anesthetized rats (paralyzed and ventilated) produced a pressor response (26.5 +/- 1.6 mmHg, n = 7) and a transient depression of phrenic nerve discharge (90 +/- 8%, n = 5). Microiontophoretic applications of cyanide (less than or equal to 100 nA, 5-40 s) excited the RVL-spinal sympathoexcitatory neurons (31 out of 31). The response was dose dependent, reversible, independent of the baroreflex input to these neurons, and different from the responses of units with spontaneous discharge synchronized with the lung inflation or with unidentified function. The cyanide-induced excitation of the RVL-spinal sympathoexcitatory neurons was reversibly abolished by CO2+, applied iontophoretically at a dose at which the baroreflex inhibition of these neurons was not markedly affected whereas iontophoretic applications of kynurenic acid, a glutamate receptor antagonist, did not alter the response of the RVL-spinal sympathoexcitatory neurons to cyanide. It was concluded that cyanide induces a rapid Ca(2+)-dependent response of the RVL-spinal sympathoexcitatory neurons, which may underlie the cellular mechanism of these neurons in responding to ischemia-hypoxia.

Animals↗
PubMed1992

Isolation and characterization of imidazoline receptor protein from bovine adrenal chromaffin cells.

We sought to isolate and partially purify proteins corresponding to the binding element of the imidazoline receptor (IR) from adrenal chromaffin cell membranes. These cells express IRs of the I-2 subclass and not alpha 2-adrenergic receptors. Proteins were solubilized in 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate-containing buffer and were assayed by binding of [3H]idazoxan, an imidazoline radioligand. Two ligand affinity resins, p-aminoclonidine-Trisacryl GF-2000 (PAC-ReactiGel) and idazoxan-PharmaLink agarose (IDA-agarose), were synthesized. These allowed purification by single-step affinity chromatography of a major receptor binding protein component of 70 kDa, as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and [3H]idazoxan binding assay. The purified imidazoline-binding proteins from IDA-agarose and PAC-ReactiGel had similar affinities for the radioligand [3H]idazoxan (Kd = 3.7 and 4.9 nM, respectively) and a displacement profile, showing sensitivity to imidazoline agents (cirazoline > clonidine) and insensitivity to catecholamines and adrenergic agents (epinephrine approximately rauwolscine), that was similar to that of the intact membrane receptor. The imidazoline-binding protein did not bind to concanavalin A, suggesting that it may not be glycosylated or that the sugar moieties present are not recognized by this lectin. The results indicate that IR and alpha 2 receptor proteins may be biochemically distinct and that IDA-agarose and PAC-ReactiGel columns are useful for purification of sufficient quantities of imidazoline-binding proteins to allow for structural and functional studies of the IR.

Adrenal Glands↗
PubMed1991

Effects of clonidine and other imidazole-receptor binding agents on second messenger systems and calcium influx in bovine adrenal chromaffin cells.

Clonidine and related imidazoline compounds bind to alpha 2-adrenergic as well as to newly described non-adrenergic imidazole/imidazoline receptors in brain and peripheral tissues. The present study was undertaken to identify the signal transduction mechanism coupled to this new class of receptors (imidazole receptors) using bovine adrenal chromaffin cells. Clonidine did not modify the basal or forskolin-stimulated production of cyclic AMP (cAMP), suggesting the absence of functionally active alpha 2-adrenergic receptors in adrenal chromaffin cells. Clonidine also failed to modify the basal and GTP gamma S- or carbachol-stimulated increase in phosphoinositide hydrolysis. However, clonidine increased significantly the production of cyclic GMP (cGMP) as well as the uptake of 45Ca2+. The cGMP response to clonidine was slower (peak at 15 min) and smaller (only about 50% over control) than the response to acetylcholine and was not shared by other agents that bind to imidazole receptors. In contrast, all agents that bind to imidazole receptors increased the influx of 45Ca2+ into chromaffin cells. It is concluded that (a) alpha 2-adrenergic and imidazole receptors are functionally distinct and linked to different signal transduction mechanisms; (b) the classical G-protein coupled soluble second messenger systems are not coupled to imidazole receptors; (c) clonidine may increase cGMP by a non-receptor-mediated intracellular action; and (d) imidazole receptors may regulate intracellular calcium levels through an ion regulating system that may be different from calcium channels.

Adrenal Glands↗