Biomedical subjects

G Krishna

Publications and source records attributed to G Krishna.

At least 55 records · Page 3Linked to original sources

PubMed1995

An in vivo/in vitro method for assessing micronucleus and chromosome aberration induction in rat bone marrow and spleen. 2. Studies with chlorambucil and mitomycin C.

An in vivo/in vitro system using rat bone marrow cells and spleen cells to assess micronucleus (MN) and structural chromosome aberrations (SCA) simultaneously (Moore et al., 1995) was further developed. In two separate experiments, two rats/dose/experiment were treated i.p. with 0, 5, 10 and 15 mg chlorambucil (CA)/kg or with mitomycin C (MMC) at 0, 1, 2, 4 mg/kg (experiment 1) or 0, 4, 6, and 8 mg/kg (experiment 2) and killed 6 h later. Cultures were then established in the presence of growth stimulants (interleukin-3 and granulocyte-macrophage colony stimulating factor for bone marrow; lipopolysaccharide and concanavalin A for spleen) and cytochalasin B, a cytokinesis inhibitor. Bone marrow cells were harvested 24 h after establishment of cultures, while spleen cells were harvested at 48 h. In addition, spleen cells were concurrently assayed for chromosome aberrations. With the MN endpoint, spleen cells appeared more sensitive than bone marrow cells to the effects of CA due both to a lower background and an increased response. For MMC, bone marrow cells exhibited both a higher background of MN and a greater numerical response than did spleen cells. However, on the basis of a fold-increase over control values, spleen cells were more sensitive than bone marrow cells. In general, the MN endpoint appeared more sensitive than the SCA in spleen cells after treatment with CA or MMC. Thus, the approach described here shows greater potential in detecting genotoxicity.

Animals↗

PubMed1995

Expression of mRNA for atrial natriuretic peptide receptor-A in human liver: detection using RT-PCR.

cDNA preparations obtained from human liver poly A+ RNA by reverse transcription were subjected to polymerase chain reaction. Primers used in the reaction were designed from the reported cDNA sequence for human placental atrial natriuretic peptide receptor-A (ANPRA). Sequence analysis of the amplified product (approximately 700 bp) showed 100% identity to the 2476-3189 bp region of the reported cDNA sequence of human placental ANPRA. Northern blot analysis of human liver poly A+ RNA fractions showed a hybridization signal at approximately 4.4 kb, identical to the signal obtained from the poly A+ RNA fractions of human placenta. These results indicate the possible mRNA expression for atrial natriuretic peptide receptor-A in human liver.

Atrial Natriuretic Factor↗

PubMed1994

Human retina expresses both constitutive and inducible isoforms of nitric oxide synthase mRNA.

The present study provided evidence for the presence of two forms of nitric oxide synthase(NOS) gene in the human retina. Expression of retinal constitutive type(rbNOS) and inducible type(riNOS) of NOS was detected in human retinal poly A+RNA by reverse transcriptase polymerase chain reaction (RT-PCR) method. The deduced amino acid sequence of the human retinal rbNOS showed more than 99% homology with human brain bNOS and that of riNOS was identical to the chondrocytes inducible iNOS with the exception for one amino acid. These differences in amino acid sequences of rbNOS and riNOS, with their counterparts in human brain and human chondrocytes sequences, were only in the non-cofactor binding sites. Northern blot analysis of the human retinal poly A+RNA and total RNA, using the PCR-amplified riNOS probe revealed the existence of riNOS message with the appearance of the band with the expected size of 4.4kb, while the message for rbNOS was not detectable. This was the first report of the deduced nucleotide sequence identification of two NOS genes from a human tissue, while there had been earlier reports from culture cells.

Adolescent↗

PubMed1994

In vivo generation of hydroxyl radicals and MPTP-induced dopaminergic toxicity in the basal ganglia.

The in vivo generation of .OH free radicals in specific brain regions can be measured by intracerebral microdialysis perfusion of salicylate, avoiding many of the pitfalls inherent in systemic administration of salicylate. Direct infusion of salicylate into the brain can minimize the hepatic hydroxylation of salicylate and its contribution to brain levels of 2,5-DHBA. Levels of 2,5-DHBA detected in the brain dialysate may reflect the .OH adduct plus some enzymatic hydroxylation of salicylate in the brain. After minimizing the contribution of enzyme and/or blood-borne 2,5-DHBA, the present data demonstrate the validity of the use of 2,3-DHBA and apparently 2,5-DHBA as indices of .OH formation in the brain. Therefore, intracranial microdialysis of salicylic acid and measurement of 2,3-DHBA appears to be a useful .OH trapping procedure for monitoring the time course of .OH generation in the extracellular fluid of the brain. These results indicate that nonenzymatic and/or enzymatic oxidation of the dopamine released by MPTP analogues in the extracellular fluid may play a key role in the generation of .OH free radicals in the iron-rich basal ganglia. Moreover, a site-specific generation of cytotoxic .OH free radicals and quinone/semiquinone radicals in the striatum may cause the observed lipid peroxidation, calcium overload, and retrograde degeneration of nigrostriatal neurons. This free-radical-induced nigral injury can be suppressed by antioxidants (i.e., U-78517F, DMSO, and deprenyl) and possibly hypothermia as well. In the future, this in vivo detection of .OH generation may be useful in answering some of the fundamental questions concerning the relevance of oxidants and antioxidants in neurodegenerative disorders during aging. It could also pave the way for the research and development of novel neuroprotective antioxidants and strategies for the early or preventive treatment of neurodegenerative disorders, such as Parkinson's disease (Wu et al., this issue), amyotrophic lateral sclerosis, head trauma, and possibly Alzheimer's cognitive dysfunction as well. In conclusion, this in vivo free-radical trapping procedure provides evidence to support a current working hypothesis that a site-specific formation of cytotoxic .OH free radicals in the basal ganglia may be one of the neurotoxic mechanisms underlying nigrostriatal degeneration and Parkinsonism caused by the dopaminergic neurotoxin MPTP. Addendum added in proof: The controversy concerning possible neurotoxic and/or neuroprotective roles of NO. in cell cultures was discussed and debated at the symposium (Wink et al., this issue; Dawson et al., this issue; Lipton et al., this issue).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Expression of mRNA for atrial natriuretic peptide receptor guanylate cyclase (ANPRA) in human retina.

1. Guanylate cyclase plays an important role in the visual cycle. Here we report the mRNA expression for the atrial natriuretic peptide receptor type A form of guanylate cyclase (ANPRA) in human retina. 2. Polymerase chain reaction using two sets of primers on the cDNAs reverse-transcribed from human retinal poly(A)+ RNA amplified two products under two different reaction conditions. The primers used in the reaction were designed from the reported sequence of human placental ANPRA cDNA. 3. Sequencing of the amplified products showed 100% sequence homology to the human placental ANPRA gene. Northern blot analysis indicated the presence of a 4.4-kb ANPRA mRNA in human retina, similar to that present in human brain.

Base Sequence↗

PubMed1994

Comparison of the pharmacokinetics of an ondansetron solution (8 mg) when administered intravenously, orally, to the colon, and to the rectum.

Ondansetron, an antagonist of the serotonin type 3 (5-HT3) receptor, is indicated for the treatment of chemotherapy-induced emesis. This study compares the pharmacokinetics, especially the bioavailability, of an ondansetron 8-mg solution when administered intravenously, orally, to the colon via nasogastric intubation, and to the rectum using a retention enema. Six healthy, male volunteers received ondansetron infused into the colon during the first treatment period. These subjects then received the remaining three treatments in random order, with a minimum 1-week washout period between treatments. Serial plasma samples were obtained for up to 24 hr after dosing in each treatment period. Absolute bioavailability after the oral dosing, colonic infusion, and rectal administration averaged 71 +/- 14, 74 +/- 26, and 58 +/- 18%, respectively. These values were not significantly different (P > 0.05). Values of Tmax and Cmax were also not significantly different among the nonparenteral routes. Mean absorption half-lives were 0.66, 1.1, and 0.75 hr after the oral, colonic, and rectal administrations, respectively. These results indicate that ondansetron is well absorbed in the intestinal segments studied including the upper small intestine, the colon, and the rectum and that sustained-release and suppository formulations of ondansetron are feasible.

Administration, Oral↗

PubMed1994

Cloning and sequencing of heat shock factor (HSF1) cDNA from human retina.

Transcription of heat shock genes takes place in response to the exposure of cells to elevated temperatures or other stress conditions. Heat shock transcription factor (HSF) plays an important role in the activation of such transcription. We report here the identification of human heat shock factor from human retina by RT-PCR and cloning studies. Human retinal poly A+ RNA was reverse transcribed and the cDNAs thus obtained were subjected to PCR using a set of primers designed from the reported cDNA sequence for human HSF1. The amplified product showed 100% sequence identity with the appropriate region of HSF1. A human retinal cDNA library was screened to isolate the full length cDNA for heat shock factor, which showed 100% sequence identity to that reported for human HSF1. Northern blot analysis showed the size of human retinal HSF to be approximately 2.4 kb.

Amino Acid Sequence↗

PubMed1994

Anaesthetic considerations for magnetic resonance imaging.

Magnetic resonance imaging (MRI) has become an increasingly popular non-invasive radiological diagnostic procedure, with several distinct advantages over computerised tomography (CT). The images are produced using a strong (1.5-Tesla) magnetic field and radiofrequency (RF) pulses. Due to the effects of the strong magnetic field, certain groups of patients with implanted ferromagnetic objects and women in their first trimester of pregnancy are precluded from undergoing MRI. While most of the patients undergo MRI awake or with light sedation, few need heavy sedation or general anaesthesia. The problems related to anaesthesia in MRI include the constant presence of a strong magnetic field, the RF pulses and their effect on the anaesthesia machine, monitoring devices, magnetically coded material, and loose ferromagnetic objects. In this article, the current availability of MRI-compatible anaesthesia machine, various monitoring devices, and safe conduct of anaesthesia during MRI for patients of all ages are discussed. In addition, the implications of the strong magnetic field on patient resuscitation inside the MRI suite and the recommended procedure for a successful outcome are outlined.

Adult↗

PubMed1993

Studies on the interaction of the dye, stains-all, with individual calcium-binding domains of calmodulin.

We show that the calcium-mimic dye, Stains-all, is a convenient probe to study the structural features of the individual calcium-binding sites of calmodulin (CaM) and related calcium-binding proteins (CaBP). These peptides bind the dye in their calcium-binding sites, and induce a circular dichroism (CD) band in the bound dye in the 620 nm (J band) region, which is abolished upon the addition of calcium. Replacement of Asp by Asn in the + x position of the weaker calcium-binding site (site I of CaM) abolishes the dye binding, while the same change in the higher affinity site IV attenuates the binding of the dye and does not abolish it. Replacement of Tyr in site IV with Trp does not distort the geometry, although it increases the dye binding affinity.

Amino Acid Sequence↗

PubMed1992

Expression of guanylate cyclase-A mRNA in the rat retina: detection using polymerase chain reaction.

A technique based on RNA-PCR was successfully employed for the detection of guanylate cyclase-A (GC-A) mRNA in the rat retina. Three sets of primers designed from the published cDNA sequence of rat brain guanylate cyclase-A (GC-A) produced amplification products of expected sizes from the retina as well as brain. Analysis of retinal PCR products yielded a 970 bp sequence, which showed 100% homology to the cDNA sequence of GC-A (2343-3312 bp region). Northern blot analysis was not very sensitive for the detection of GC-A mRNA in the retina. The results indicate that the mRNA for GC-A (or a closely related form) is probably expressed in the retina, but at a lower level than that found in the brain.

Animals↗

PubMed1992

Genotoxicity assessment of pirmenol, a new antiarrhythmic drug.

The genotoxicity of pirmenol was tested in the E. coli and S. typhimurium mutagenesis assay, an in vitro mammalian cell chromosome-aberration assay and an in vivo mouse micronucleus assay. The E. coli tester strain WP2s was exposed to concentrations of pirmenol as high as 10,000 micrograms/plate both in the absence (S9-) and presence (S9+) of metabolic activation. Five strains of S. typhimurium (TA98, TA100, TA1535, TA1537, TA1538) were exposed to concentrations of pirmenol as high as 5000 micrograms/plate in the absence and presence of S9. Pirmenol was not mutagenic toward either E. coli or S. typhimurium. Chinese hamster lung V79 cell cultures were exposed to pirmenol at concentrations of 500-2500 micrograms/ml (S9-) and 500-3000 micrograms/ml (S9+). Pirmenol increased the frequency of structural chromosome aberrations (SCAs). The minimum clastogenic concentration was 1500 micrograms/ml (both S9- and S9+) with a peak clastogenic response of 6% (S9-) and 34% (S9+) cells with aberrations. Although there were statistically significant results in the S9- experiment, the percent cells with aberration values for treated groups were within the historical control range (0-6%) of this laboratory. The observed effects in both the absence and presence of S9 appear at high concentrations compared to human circulating plasma levels of 1-3 micrograms/ml and the clastogenicity was confined to chromosome gaps and breaks. Consequently, this in vitro effect would not be expected to be reflected by either in vivo clastogenic or carcinogenic activity. This was supported by findings in the mouse micronucleus study of pirmenol in which single oral doses administered to male CD-1 mice at 5, 55, or 115 mg/kg (80% LD50) produced no statistically significant increases in the frequency of micronucleated polychromatic erythrocytes in bone marrow at 24, 48 or 72 h postdosing. Additionally, no evidence of carcinogenicity was seen in a mouse or rat bioassay.

Animals↗

PubMed1992

Simultaneous analysis of chromosome damage and aneuploidy in cytokinesis-blocked V79 Chinese hamster lung cells using an antikinetochore antibody.

A modified antikinetochore antibody technique was established in the V79 Chinese hamster lung cells to simultaneously analyze chromosome damage and aneuploidy induced by various agents. The method involved sequential treatment of slides with crest serum, fluoresceinated goat-antihuman and swine-antigoat antibodies, and propidium iodide. In this method, cytoplasm (green), nuclei or micronuclei (red), and kinetochores (yellow), are identified using the same filter setting under blue excitation (440-490 nm) with a barrier filter at 520 nm. Using this method, three agents, vinblastine (VB), X-rays, and methyl methanesulfonate (MMS) were tested for micronucleus/aneuploidy induction. An aneugen, VB and a clastogen, X-rays, induced predominantly kinetochore positive (K+) and negative (K-) micronucleated binucleate (MNBN) cells, respectively, in a dose-dependent fashion. An alkylating agent, MMS, produced both K+ and K- MNBN cells. These results are comparable with the results reported in the literature on these compounds using various methods and thus demonstrate the usefulness of this assay in distinguishing clastogenicity from aneugenicity.

Aneuploidy↗

PubMed1992

Simultaneous evaluation of clastogenicity, aneugenicity and toxicity in the mouse micronucleus assay using immunofluorescence.

An improved antikinetochore antibody technique was established in the mouse micronucleus assay to simultaneously evaluate toxicity, clastogenicity and aneugenicity induced by various test agents. The procedure involved the use of cellulose column fractionated cytospun slides for analysis. The staining method consisted of sequential treatment of slides with crest serum, fluorosceinated goat-antihuman and swine-antigoat antibodies, and propidium iodide. In this method, polychromatic erythrocytes (PCEs, dark red), normochromatic erythrocytes (NCEs, green), chromosome(s)/fragments/micronuclei (orange), and kinetochores (yellow), are identified using the same filter setting under blue excitation (440-490 nm) with a barrier filter at 520 nm. Using this method, three agents, cyclophosphamide, X-rays and vincristine were tested for micronucleus/aneuploidy induction and bone marrow toxicity. The aneugen, vincristine, and clastogens, X-rays and cyclophosphamide, induced predominantly kinetochore positive (K+) and negative (K-) micronucleated PCEs, respectively. At the doses tested, cyclophosphamide caused a slight but statistically significant decrease in PCEs in females, and other agents did not produce any severe bone-marrow toxicity in either male or female mice. These results are comparable with the results reported in the literature on these compounds with various methods and thus demonstrate the usefulness of this assay in distinguishing clastogenicity from aneugenicity and in evaluating toxicity.

Aneuploidy↗

PubMed1992

Intracranial microdialysis of salicylic acid to detect hydroxyl radical generation through dopamine autooxidation in the caudate nucleus: effects of MPP+.

Ringer's solution containing salicylic acid (5 nmol/microliters/min) was infused directly through an intracranial microdialysis probe to detect the generation of hydroxyl radicals (.OH) reflected by the formation of dihydroxybenzoic acids (DHBA) in the caudate nucleus of anesthetized rats. Brain dialysate was assayed for dopamine, 2,3-, and 2,5-DHBA by a high-pressure liquid chromatography-electrochemical (HPLC-EC) procedure. 1-Methyl-4-phenylpyridinium ions (MPP+, 0 to 150 nmol) increased dose-dependently the release of dopamine and the formation of DHBA. A positive linear correlation between the release of dopamine and the formation of 2,3- or 2,5-DHBA was observed (R2 = .98). The present results demonstrate the validity of the use of not only 2,3-DHBA but also 2,5-DHBA as an in vivo index of oxidative damage generated by reactive .OH radicals. In conclusion, the present study demonstrates a novel use of intracranial microdialysis of salicylic acid to assess the oxidative damage elicited by .OH in living brain.

1-Methyl-4-phenylpyridinium↗

PubMed1992

Anesthesia for the newborn and ex-preterm infant.

This article addresses the pertinent aspects of neonatal physiology and pharmacology, general considerations in the anesthetic care of surgical neonates, management details of selected neonatal surgical lesions, and anesthetic considerations for the ex-preterm infant.

Abdominal Muscles↗

PubMed1992

Malignant hyperthermia.

Malignant hyperthermia is a rare disease triggered by succinylcholine and the volatile anesthetic agents in genetically predisposed individuals. Recent studies have implicated an abnormality in the calcium release channel of the sarcoplasmic reticulum in skeletal muscle as the likely etiology. Genetic studies have narrowed the search for the chromosomal abnormality to human chromosome 19. Although the mortality from this disorder has dramatically decreased in the past decade due to the discovery of dantrolene, elective diagnosis of the disorder is only now appearing on the horizon.

Anesthesia↗

PubMed1991

Increased toxicity of anthracycline antibiotics induced by calcium entry blockers in cultured cardiomyocytes.

Calcium channel blocking drugs have been reported to reduce survival rate of laboratory animals treated with cardiotoxic antitumor anthracyclines. In order to elucidate the mechanisms of this drug interaction, cell toxicity of the anthracyclines, doxorubicin and daunorubicin, was evaluated in primary cultures of cardiac myocytes isolated from neonatal rats. Low concentrations of extracellular calcium ([Ca2+]0) and addition of calcium entry blockers (nifedipine or flunarizine) potentiated myocardial toxicity of anthracyclines as assessed by the release of lactate dehydrogenase from the cells. Accumulation of anthracyclines in the cardiomyocytes was increased by calcium entry blockers (nifedipine, flunarizine, and verapamil) and by low [Ca2+]0; efflux of [3H]daunorubicin from myocardial cells was inhibited by nifedipine. At a dose that exerts only modest calcium channel activity, R-verapamil failed to affect doxorubicin accumulation in cardiomyocytes, whereas the calcium channel activator, (+/-)-Bay K-8644, reduced the retention of anthracyclines; the calcium channel activity is thus required in order to increase the accumulation of anthracyclines in myocardial cells. Calcium channel blockers are also known to increase intracellular retention and toxicity of chemotherapeutic drugs in multidrug resistant tumor cells by inhibiting the efflux of cytotoxic agents from cells; however, the ability of the interacting drugs to inhibit the efflux of chemotherapeutic agents from tumor cells is not dependent on the calcium channel blocking activity. Therefore, the mechanism(s) by which calcium channel blocking drugs increase the accumulation of anthracyclines in resistant tumor cells and myocardial cells may be different. In accordance with previous investigations, the present in vitro study confirmed that anthracycline-induced cardiotoxicity may be potentiated by calcium channel blocking drugs. This indicates that, in the association of antineoplastic drugs with agents that reverse multidrug resistance, the potential exists for enhanced damage of normal cells and tissues; further studies are needed to evaluate the relevance of this adverse interaction.

Animals↗

PubMed1991

Induction of micronuclei in rat bone marrow by four model compounds.

Studies have been performed to determine the dose and sampling time responses of micronuclei after Sprague-Dawley rats were treated with triethylenemelamine, mitomycin C. dimethylbenzanthracene, and vincristine by a single intraperitoneal injection. Three doses were tested for each compound. Animals were sacrificed 24, 48, and 72 h after chemical treatment. Slides prepared from the bone marrow were stained with May-Gruenwald and Giemsa stains. The number of micronucleated polychromatic erythrocytes among 2,000 polychromatic erythrocytes (PCEs) and the ratio of PCEs to normochromatic erythrocytes were determined for each animal. The results show that all four compounds cause micronucleus formation in rat bone marrow. The peak response sampling time, either 24 or 48 h posttreatment, is dependent on the chemical as well as the dose. In all cases, however, an increase in the micronucleated PCEs was detected 24 h after chemical treatment. These results seem to indicate that two sampling times, 24 and 48 h, may be adequate for the micronucleus assay using rat bone marrow cells.

9,10-Dimethyl-1,2-benzanthracene↗