Biomedical subjects

J Y Chan

Publications and source records attributed to J Y Chan.

At least 127 records · Page 7Linked to original sources

PubMed1990

Interaction between angiotensin III and alpha 2-adrenoceptors of the medulla oblongata involved in cardiovascular regulation in the rat.

We evaluated, in adult, male Sprague-Dawley rats anesthetized with pentobarbital sodium, possible interaction between angiotensin III (AIII) and the alpha 2-adrenoceptors in the medulla oblongata that are involved in cardiovascular regulation. The hypotensive and negative chronotropic and inotropic actions of the alpha 2-adrenoceptor agonist, guanabenz, were used as our experimental index. Intracerebroventricular (i.c.v.) administration of AIII (100 or 200 pmol) significantly attenuated the cardiovascular suppressive effects of the aminoguanidine compound (25 or 50 micrograms/kg, i.v.). Bilateral microinjection of AIII (20 or 40 pmol) to the nucleus reticularis gigantocellularis (NRGC), a medullary site believed to be intimately related to the antihypertensive action of guanabenz, produced similar results. In addition, i.c.v. administered AIII (200 pmol) altered the effects of guanabenz on the arterial pressure-related neurons in the NRGC, in a manner that paralleled the blunted vasodepressive action of the aminoguanidine compound by the heptapeptide. When applied microiontophoretically, AIII also significantly decreased the responsiveness of arterial pressure-related neurons in the NRGC to guanabenz. These findings suggest that AIII may interact with the alpha 2-adrenoceptors located in the NRGC that are involved in central cardiovascular regulation.

Angiotensin II↗

PubMed1990

Tonic reduction in central alpha 2-adrenoceptor activity by endogenous angiotensin III in the rat.

We evaluated the possible interactions between central alpha 2-adrenoceptors and endogenous angiotensin III (AIII) in Sprague-Dawley rats anesthetized with pentobarbital sodium (50 mg/kg, i.p.). The cardiovascular suppressive effects of the alpha 2-adrenoceptor agonist, guanabenz, were used as our experimental index for alpha 2-adrenoceptor activity. Intracerebroventricular (i.c.v.) administration of AIII (100 or 200 pmol) attenuated the hypotensive and negative inotropic and chronotropic actions of guanabenz (100 micrograms/kg, i.v.). Blocking the endogenous activity of the heptapeptide with its specific antagonist, Ile7-AIII (50 or 100 nmol, i.c.v.), on the other hand, potentiated the circulatory inhibitory efficacy of the aminoguanidine compound. These modulatory effects were essentially duplicated by bilateral microinjection of AIII (20 or 40 pmol) or Ile7-AIII (10 or 20 nmol) into the nucleus reticularis gigantocellularis (NRGC), a medullary site that is critically involved in the cardiovascular suppressive actions of guanabenz. I.c.v. injection of bestatin (200 nmol) also reduced the circulatory depressive potency of guanabenz. This effect was respectively enhanced and reduced when the aminopeptidase inhibitor was given simultaneously with AIII (200 pmol) and Ile7-AIII (100 nmol). These results suggest that the endogenous AIII may exert a tonic inhibition on the alpha 2-adrenoceptors in in the NRGC that are involved in cardiovascular regulation.

Angiotensin III↗

PubMed1990

Selective effect of zinc compared to other divalent metals on L-triiodothyronine binding to rat c-erbA alpha and beta proteins.

The effects of zinc and other divalent metals on the [125I]T3 binding to rat c-erbA alpha and beta recombinant proteins were assessed. The addition of ZnCl2 caused a reversible and dose-dependent inhibition of [125I]T3 binding to rc-erbA beta proteins with half maximum inhibition occurring at 50-100 microM, but no significant effect on [125I]T3 binding to rc-erbA alpha under the same assay conditions. Scatchard analysis revealed a decrease in [125I]T3 binding capacity to beta protein without marked change in Kd values in presence of zinc. Moreover, significant inhibitions of [125I]T3 binding to both alpha and beta proteins were observed in the presence of 100 microM of either MnCl2, CdCl2 or CuCl2, but not MgCl2. Thus, the selective effect of zinc compared to other divalent metals to inhibit T3 binding to rc-erbA beta, but not alpha, proteins was documented and suggest a possible regulatory role for zinc in modulating the intracellular action of thyroid hormone.

Animals↗

PubMed1989

Cloning and characterization of a cDNA that encodes a 70-kDa novel human thyroid autoantigen.

cDNA clones were isolated by screening a human thyroid carcinoma lambda gt11 library with immunoglobulins purified from serum of a patient with autoimmune Graves' disease. One clone (ML8) containing a 1.25-kilobase (kb) insert hybridized with a single 2.0-kb poly(A+) mRNA in human thyroid and lymphocytes but not in human brain, liver, kidney, or muscle. In addition, this probe also hybridized with a single 2.0-kb poly(A+) mRNA from a rat thyroid cell line (FRTL-5). An apparently full length 2,074-base pair (bp) human cDNA was obtained and sequenced. The nucleotide sequence of the 2,074-bp cDNA includes a 5'-noncoding sequence of 17 bp, a 1827-bp open reading frame, and a 222-bp 3'-noncoding sequence. The canonical polyadenylation signal AATAAA is present 18 bp upstream of the poly(A) tail. This cDNA encodes a 69,812-dalton protein with two potential N-linked glycosylation sites and at least one potential membrane spanning domain. Immunoprecipitation of the in vitro translated protein by sera from several patients with Graves' disease argues that the 69,812-dalton protein is an autoantigen.

Amino Acid Sequence↗

PubMed1989

Passive electrical properties of spontaneously active neurons in the nucleus reticularis gigantocellularis of the cat.

We evaluated in chloralose-urethane anesthetized cats the passive electrical properties of 25 spontaneously active neurons in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata. Compared to other mammalian brain regions, these reticular cells in general possessed higher input resistance, shorter membrane time constant and first equalizing time constant, and longer somatodendritic electrotonic length factor. It is discussed that, by providing a synaptic machinery for quick and sensitive response to afferent inputs and an efficacious interplay between temporal and spatial summation, these electrical membrane properties may account for the spontaneous and irregular discharge pattern characteristic of the NRGC neurons.

Action Potentials↗

PubMed1989

Receptors of the thyroid: the thyrotropin receptor is only the first violinist of a symphony orchestra.

A basic reason for undertaking these studies was to further our knowledge of the structure and function of the TSH receptor as well as its interaction with other receptors on thyroid cells. The multiplicity of observations suggests the approach is bearing fruit, does not provide a simple answer, and can have pitfalls. We hope they may also contribute to understanding the structure and function of autoantigens in Graves' disease and glycoprotein hormone receptors in general. The authors are grateful to their collaborators in the National Dental Institute, particularly Drs. Bellur Prabhakar, Edward Oates, and Abner Notkins, in the National Cancer Institute, Drs. W. O. McBride and M. Lerman for their contributions to the cloning studies.

Amino Acid Sequence↗

PubMed1989

Sequence and chromosomal assignment of a novel cDNA identified by immunoscreening of a thyroid expression library: similarity to a family of mitochondrial solute carrier proteins.

An immunoglobulin G (IgG) preparation of the serum from a patient with active Graves' disease was used to isolate cDNA clones from a lambda gt11 cDNA library of human thyroid follicular carcinoma tissue by immunoscreening. One of these clones, hML-7, is further characterized herein by sequencing, Northern analysis, and chromosomal mapping. The clone reacted with IgG preparations from the sera of 14 of 19 patients with active Graves' disease but not with IgG preparations from 11 normal individuals, three patients with toxic thyroid adenoma, and three with rheumatoid arthritis. The hML-7 cDNA hybridized to a 3.6 kilobase (kb) mRNA transcript in poly(A+) RNA preparations from human thyroid tissue and continuously cultured rat thyroid cells; expression of this transcript in rat FRTL-5 thyroid cells was positively regulated by TSH. The 3.6 kb transcript was less abundant in rat liver (BRL3A) cells or differentiated rat (L6) myoblasts than in cultured rat thyroid cells and was not detectable in mouse L-M fibroblasts, human IM-9 lymphocytes, Chinese hamster ovary cells, or human cervical carcinoma cells. The cDNA from hML-7 was sequenced and compared with the sequence of cross-hybridizing cDNA clones isolated from human Graves' thyroid and rat FRTL-5 thyroid cell lambda gt11 expression libraries. A 1.05 kb open reading frame, which is highly conserved between human and rat, was defined. The predicted amino acid sequence of 348 residues exhibited a strong homology with the mitochondrial ADP/ATP carrier protein (adenine nucleotide translocase; ADP/ATP translocator) and with two other members of the same mitochondrial protein family, the phosphate carrier and the hydrogen ion uncoupling protein. The gene represented by the hML-7 cDNA has been assigned to human chromosome 10.

Amino Acid Sequence↗

PubMed1988

Defective DNA ligase I in Bloom's syndrome cells. Simultaneous analysis using immunoblotting and the ligase-[32P]AMP adduct assay.

Cells from patients with Bloom's syndrome (BS), an autosomal recessive disorder associated with an increased risk of cancer, exhibit genomic instability. Increased numbers of sister-chromatid exchanges (SCE) and delayed DNA chain maturation are typically observed in BS cells. To elucidate the basis for the previously reported decreased DNA ligase I activity in BS cells, simultaneous immunoblot and activity assays for ligase-[32P]AMP adduct formation were performed on extracts from BS and normal lymphoblastoid cell lines. Immunoblot analysis using antibody to DNA ligase I indicate that the amount of the major reactive protein (98 kDa) in normal and BS cells is similar. However, a 50-90% decrease was observed in the ligase activity of the 98-kDa polypeptide in high-SCE BS cells (HG1514 and GM3403c). In contrast, the activity in low-SCE BS cells (HG1554) did not differ significantly from that in normal cells. The data, together with mixing experiments, indicate that the defect in BS ligase I is due at least in part to the loss of ATP binding and/or hydrolytic activity and not to differences in numbers of protein molecules or inhibitory substances. These results suggest that mutation of the DNA ligase I gene may account for the primary metabolic defect in BS.

Adenosine Monophosphate↗

PubMed1988

Reduction in baroreceptor reflex response by angiotension III and its modification by Ile7-angiotensin III and bestatin in the rat.

We evaluated the participation of endogenous brain angiotensin III (AIII) in central cardiovascular regulation, using the intracerebroventricular injection technique in Sprague-Dawley rats anesthetized with pentobarbital sodium (50 mg/kg, i.p.). AIII (100 pmol) promoted an elevation in systemic arterial pressure and a reduction in the baroreceptor reflex (BRR) response. Its specific antagonist, Ile7-AIII (100 nmol), and the aminopeptidase inhibitor, bestatin (200 nmol), on the other hand, augmented the response of the same reflex. The suppressive action of AIII (100 pmol) on the BRR was attenuated, and the enhancing effect of Ile7-AIII (100 nmol) was potentiated, however, when these two peptides were administered simultaneously with bestatin (200 nmol). All these events were significantly different from their controls during the first 10-15 min following injection, parallel to the time course of a discernible action of AIII on systemic arterial pressure. We discussed that the endogenous AIII in the central nervous system may participate in cardiovascular control by tonically inhibiting the BRR, in concert with other brain neuropeptides.

Angiotensin II↗

PubMed1988

Angiotensin II receptors in the lumbar spinal cord of the rat.

Locations of cells responsive to microiontophoretically applied angiotensin II (AII) were compared to distributions of AII receptor binding sites identified by autoradiography in the lumbar enlargement region of the rat spinal cord. Angiotensin II receptor binding sites were densely concentrated in the superficial layers of the dorsal horn. Considerably lower densities of binding sites were present in the remaining gray matter. Effects of microiontophoretically applied AII on lumbar spinal cord cells did not vary with location within the gray matter. AII facilitated firing of most cells in the lumbar cord whether the cells were in superficial or deeper laminae of the dorsal horn or in the ventral horn. The distribution of AII binding sites and the distribution of cells that were responsive to AII suggest that AII may play a role in modulating both sensory and motor functions of the spinal cord.

Angiotensin II↗

PubMed1987

Effects of bestatin on the central cardiovascular regulatory mechanisms in the rat.

We evaluated the effects of bestatin, the specific aminopeptidase-B and leucine aminopeptidase inhibitor, on the central cardiovascular regulatory mechanisms in Sprague-Dawley rats anesthetized with pentobarbital sodium (40 mg/kg, i.p.). Intracerebroventricular injection of bestatin (100 or 200 nmol/5 microliters) consistently elevated the basal systemic arterial pressure and heart rate. At the same time, this degradative enzyme blocker increased the sensitivity of the baroreceptor reflex responses as well as the efficacy of the modulatory actions of the medullary nucleus reticularis gigantocellularis on these reflexes. We speculate that enhancing the tonic activities of the endogenous neuropeptides in the brain by protecting them from their catabolic enzymes may affect the central cardiovascular regulatory machinery by modifying the operations of the baroreceptor feedback controls and their modulatory mechanisms.

Animals↗

PubMed1987

Serotonergic and non-serotonergic raphe neurons projecting to the feline lumbar and cervical spinal cord: a quantitative horseradish peroxidase-immunocytochemical study.

A quantitative study of raphe-spinal neurons and serotonergic neurons in 3 medullary raphe nuclei in the cat indicates that more than 80% of the raphe-spinal neurons that project to the spinal cord are serotonergic raphe-spinal neurons in each of the nuclei. More than 85% of the descending raphe-spinal neurons in the two caudal nuclei, nucleus raphe pallidus and nucleus raphe obscurus, are serotonergic, whereas 75% of the raphe-spinal neurons in the more rostrally placed nucleus raphe magnus contain serotonin (5-HT). These results are discussed in relation to descending systems containing both neuropeptides and 5-HT and collateralizing to several spinal segments.

Animals↗

PubMed1987

Interactions between guanabenz and clonidine in their antinociceptive effects in the rat.

Based on the hot-plate algesiometric assay in conscious Sprague-Dawley rats, we observed that both guanabenz and clonidine, at a subcutaneous dose of 5 and 1 mg/kg, respectively, exhibited significant antinociceptive potencies. Paradoxical actions on the hot-plate responses, however, were exerted by guanabenz at lower doses, varying from hyperalgesia (1 mg/kg) to no effect (2 mg/kg). A pretreatment of clonidine (1 mg/kg) substantially potentiated the antinociceptive efficacy of the two latter doses, but failed to further augment the pain-suppressive action of guanabenz at 5 mg/kg. These interactive effects of the two alpha-adrenoceptor agonists suggest that they may share a common mechanism(s) in their analgesic actions.

Analgesics↗

PubMed1987

Nuclear peptides from calf liver: large scale isolation and fractionation; control of gene expression in cell-free systems, and inhibition of growth of cells in culture.

DNA and nuclear RNA fractions contain small peptides (mol. wt. 600-1500) attached noncovalently. A large scale isolation procedure was developed for the extraction of such peptides directly from the lysed nuclei. Further purification and fractionation was performed with the chromatography on Sephadex, silica gel and H.P.L.C. C18 reverse phase columns. H.P.L.C. fractionation yielded eleven peaks. The peptides are rich in serine, glycine, alanine and acidic amino acids. They do not contain sulfur-containing amino acids. Only occasionally tyrosine, phenyalanine, histidine, arginine, and very moderate amount of lysine are found. These peptides are active in inhibiting gene expression in cell-free systems and incorporation of labeled thymidine in L 1210 murine leukemic cell culture. Thorough and exhaustive analysis demonstrated that the isolated peptides are not degradative products of histone or nonhistone chromosomal proteins.

Amino Acids↗

PubMed1986

Anatomic connections between nucleus reticularis rostroventrolateralis and some medullary cardiovascular sites in the rat.

Based on wheat germ agglutinin-conjugated horseradish peroxidase histochemistry in Sprague-Dawley rats, we identified a reciprocal and bilateral connection between the nucleus reticularis rostroventrolateralis (NRRVL) and the nucleus ambiguus. The rostral ventrolateral medulla also received bilateral inputs from the nucleus reticularis gigantocellularis (NRGC) and nucleus reticularis medullae oblongatae, a projection from the caudal ventrolateral medulla, and had a close relationship with the NRGC pars lateralis. Thus, apart from its well-established projection to the spinal sympathetic preganglionic neurons and innervation from the nucleus tractus solitarius, the NRRVL may also have rich connections with many medullary sites that participate in cardiovascular regulations.

Animals↗

PubMed1986

Anatomic and physiologic evaluation of a link between the nucleus reticularis gigantocellularis and nucleus ambiguous in the rat.

Localized microinjection of wheat germ agglutinin-conjugated horseradish peroxidase into the nucleus ambiguous (NA) of Sprague-Dawley rats retrogradely labeled neurons that were bilaterally located within the confine of the nucleus reticularis gigantocellularis (NRGC). These cells conformed with the Golgi description of cytoarchitectonic configurations and size distributions for neurons in this reticular nucleus. Furthermore, field potentials antidromically evoked at the NA by stimulating the vagus nerve were augmented by concurrent activations of bilateral NRGC sites that were themselves capable of eliciting hypotension and bradycardia. We conclude that the gigantocellular reticular nucleus may at least employ the cardiac vagal preganglionic neurons in the NA to exert its actions on the heart.

Animals↗

PubMed1986

Facilitation of lumbar monosynaptic reflexes by locus coeruleus in the rat.

The present study was initiated to delineate whether species difference exists between cats and rats in the descending influence of locus coeruleus (LC) on spinal motoneuronal activity. In male Sprague-Dawley rats anesthetized with chloral hydrate (400 mg/kg, i.p.), localized activation of LC promoted an exclusive facilitation of lumbar spinal extensor and flexor monosynaptic reflexes (MSRs). Such LC-evoked potentiations may vary in degree (37.5-147.4%), duration (70.6-72.9 ms) and latency (3.0-5.5 ms) among different animals. While minimally affecting the control MSRs, the alpha 1-adrenoceptor blocker prazosin (20 micrograms/kg, i.v.) significantly antagonized the enhancing effect of the LC on MSRs, suggesting the participation of noradrenergic neurotransmission in the process. Since these results are in general agreement with previous observations from our laboratory on the cat, we conclude that the LC exerts similar facilitatory actions on both extensor and flexor motoneuron activity of the hindlimb in at least two animal species, rat and cat.

Animals↗

PubMed1986

Regulation of expression of human granulocyte/macrophage colony-stimulating factor.

Colony-stimulating factors (CSFs) are glycoproteins that stimulate the growth of hematopoietic progenitors and enhance the functional activity of mature effector cells. Human granulocyte/macrophage colony-stimulating factor (GM-CSF) is a 22-kDa glycoprotein that stimulates the growth of myeloid and erythroid progenitors in vitro and increases the responsiveness of neutrophils, monocytes, and eosinophils to physiologic stimuli. Elucidation of the cell and tissue sources of CSFs, as well as study of their regulation of expression, is required to understand their role in physiologic and pathophysiologic states. An extensive survey of normal and neoplastic human tissues did not reveal constitutive production of detectable levels of GM-CSF mRNA in any of the 64 samples studied. Antigen- or lectin-activated T lymphocytes have been shown to produce GM-CSF; therefore, to elucidate the genetic sequences required, we constructed recombinant plasmids containing 5' flanking DNA of the GM-CSF gene linked to the marker chloramphenicol acetyltransferase gene. The recombinant constructs were transfected into a human T-cell leukemia virus type I (HTLV)-infected T-lymphoblast cell line that can be stimulated to produce high levels of GM-CSF. We show here that the 5' flanking sequences of the GM-CSF gene can direct increased expression of the chloramphenicol acetyltransferase gene in activated T-lymphoblast cells.

Acetyltransferases↗