Biomedical subjects

G Krishna

Publications and source records attributed to G Krishna.

At least 19 recordsLinked to original sources

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↗

PubMed1991

Negative halothane-caffeine contracture test in mdx (dystrophin-deficient) mice.

The genetics of malignant hyperthermia (MH) are ill-understood; however, the association of Duchenne muscular dystrophy (DMD) with MH is well known. A deficiency of dystrophin is common to both the DMD and mdx mouse, an animal model for DMD. Using muscle contracture tests for MH, we have shown that in the mdx mouse there is no MH susceptibility, suggesting the lack of a direct role of the dystrophin in the development of MH syndrome.

Abdomen↗

PubMed1991

MPTP-induced ATP depletion and cell death in neuroblastoma X glioma hybrid NG 108-15 cells: protection by glucose and sensitization by tetraphenylborate.

The toxic effect of the Parkinsonism-producing neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) was investigated using a neuronal cell culture system, namely, neuroblastoma X glioma hybrid NG 108-15. The cells were able to metabolize MPTP into its active metabolite MPP+ (1-methyl-4-phenylpyridinium ion) and to convert its derivative, 2'-methyl MPTP, to the corresponding pyridinium ion. Degenerative changes were observed in NG 108-15 cells when they were examined with a phase-contrast microscope following exposure to MPTP, MPP+, or 2'-methyl MPTP. These compounds also caused an increased leakage of LDH from the treated cells. An enhanced release of [14C]adenine nucleotides was observed from treated cells which were prelabeled with [14C]adenine. The cell death as indicated by the leakage of LDH and the release of adenine nucleotides was markedly reduced in the presence of a high concentration (25 mM) of glucose in the medium. MPTP and MPP+ induced a drastic depletion in cell ATP content prior to cell death. The ATP depletion was also reduced by the presence of a high concentration of glucose. In contrast, tetraphenylborate, a lipophilic anion, highly potentiated the ATP depletion and the subsequent cell death induced by MPTP. Thus, ATP depletion could be a major factor in MPTP-induced neuronal cell death.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1991

Simultaneous micronucleus and chromosome aberration assessment in the rat.

Using a cellulose column fractionation procedure to eliminate nucleated cells for micronucleus assessment, micronucleus and chromosome aberration endpoints in the same animal were compared in male and female rats following i.p. injection with cyclophosphamide (CP). Groups of 5 Wistar rats per sex were given single doses of CP at 0, 20, or 40 mg/kg. Two hours prior to sacrifice, animals were given colchicine (4 mg/kg) to arrest cells in metaphase. One femur from each animal was used for micronucleus assessment and the other for chromosome aberration assessment. In the micronucleus assessment, 2000 polychromatic erythrocytes (PCEs) per animal and in the chromosome aberration assessment, 50 metaphase cells per animal were scored. This experiment was repeated once. In both experiments, significant increases in micronucleated PCEs and chromosome aberrations were noted at both doses of CP in both sexes. In general, the clastogenic effects of CP were more pronounced in males than females. Both doses of CP caused a decrease in the proportion of PCEs and in mitotic index in both experiments, indicating toxicity of CP to the bone marrow. These results show the usefulness of this rat model for simultaneous evaluation of two cytogenetic endpoints in the same animal and indicate that assessment of MNPCE frequency in the bone marrow of male rats may be an appropriate model for screening test substances for in vivo clastogenic activity in this species.

Animals↗

PubMed1991

Resistance to vecuronium in patients with cerebral palsy.

To determine the electromyographic response of patients with cerebral palsy to vecuronium, 10 children (mean age, 6 yr 10 mo) without cerebral palsy and 11 children with cerebral palsy (mean age, 10 yr 3 mo) were studied. All patients were undergoing abdominal or orthopedic surgery and were anesthetized with isoflurane and nitrous oxide. The time from intravenous administration of 0.1 mg/kg of vecuronium to 25% recovery of control twitch height was 43.9 +/- 5.3 and 18.9 +/- 1.7 min (mean +/- SEM) in children without and with cerebral palsy, respectively (P less than 0.01). The authors conclude that patients with cerebral palsy are either resistant to vecuronium or have a rapid clearance as evidenced by the rapid recovery from neuromuscular blockade.

Anesthesia, Intravenous↗

PubMed1979