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Biomedical subjects

R Singh

Publications and source records attributed to R Singh.

At least 523 records · Page 29Linked to original sources
PubMed1990

Capping of U6 small nuclear RNA in vitro can be uncoupled from transcription.

U6 small nuclear RNA (snRNA) is a required component in the splicing of eukaryotic pre-mRNAs. Mammalian U6 snRNA was synthesized in vitro by T7 RNA polymerase and purified on polyacrylamide gels. This U6 RNA, with pppG on its 5' end, was accurately capped to CH3-O-pppG, when incubated with HeLa cell extract and this capping was dependent on the capping signal present within the U6 snRNA. When gamma-32P-labeled U6 RNA was used as a substrate, the U6 cap formed in vitro retained this labeled gamma-phosphate, indicating that the cap formation involves the methylation of the gamma-phosphate incorporated during transcription. U6 snRNAs with ppG or pG as their 5' ends, were not capped in this in vitro capping system. Capping of U6 snRNA in vitro requires at least two components, a heat-labile component and S-adenosylmethionine as a methyl group donor. The data presented here show that capping of U6 snRNA can be uncoupled from transcription and that the mechanism of U6 snRNA cap formation differs markedly from the capping mechanism of mRNAs and other U snRNAs where capping is cotranscriptional. While many methyltransferases have been characterized earlier, this is the first report of a methyltransferase that is specific to phosphate residues. This in vitro capping system will be useful for purification and studies on the U6 snRNA sequence-dependent methyltransferase activity.

Animals↗
PubMed1990

Production, thermal stability and immobilisation of inulinase from Fusarium oxysporum.

Fusarium oxysporum produced maximum extracellular inulinase after 9 days of its growth at 25 degrees C on a medium (pH 5.5) containing 3% fructan and 0.2% sodium nitrate. The level of this enzyme decreased on the addition of either glucose, fructose, galactose or sucrose to F. oxysporum already growing on a fructan-containing medium. A significant increase in invertase production which resulted in an increase of the invertase/inulinase (S/I) ratio, was observed on addition of inulin to this fungus growing on other carbon sources. Glycerol (10%) gave better protection to inulinase against thermal denaturation at 50 degrees C compared to ethylene glycol and sorbitol. Inulinase immobilised in polyacrylamide gel retained 45% of its original activity. The immobilised enzyme showed a higher optimum temperature (45 degrees C) compared to free enzyme (37 degrees C). The immobilised enzyme after storage at 25 degrees C for 96 h showed 58% activity. Thermal stability of entrapped inulinase increased in the presence of inulin.

Alcohols↗
PubMed1990

Suppression of serum insulin level by diazoxide does not alter serum testosterone or sex hormone-binding globulin levels in healthy, nonobese women.

Suppression of serum insulin levels with diazoxide is associated with a decrease in serum testosterone and an increase in serum sex hormone-binding globulin in obese women with the polycystic ovary syndrome. To determine whether physiologic insulin levels play a regulatory role in the androgen status of nonobese women with normal menses, the androgen status of five nonobese normal women was assessed on two occasions: during a control study and after 10 days of oral diazoxide (100 mg, three times daily) administration. Insulin release in response to 100 gm oral glucose administration decreased from 108.0 +/- 28.2 to 49.3 +/- 5.2 nmol.min/L (p = 0.05) after diazoxide administration. However, despite suppression of insulin release, diazoxide administration did not affect serum total testosterone (diazoxide, 0.73 +/- 0.10; control, 0.69 +/- 0.11 nmol/L; p = NS) or sex hormone-binding globulin (diazoxide, 79.7 +/- 16.6; control, 70.2 +/- 12.6 nmol/L; p = NS) concentrations. These observations suggest that physiologic insulin levels in nonobese healthy women do not regulate testosterone metabolism and that diazoxide does not exert a direct or independent effect on serum testosterone or sex hormone-binding globulin levels.

Administration, Oral↗
PubMed1990

Volatile fraction of neem oil as a spermicide.

The volatile, odorous fraction of neem oil coded as NIM-76 obtained by steam distillation was investigated for in vitro spermicidal activity. The data showed that the minimum concentration which inhibited spermatozoal motility was 0.25 mg/ml for rat and 25 mg/ml for human spermatozoa. The effect of the drug on spermatozoal motility was found to be dose-dependent. The activity of this drug was not altered in the presence of vaginal or cervical mucus. Intra-vaginal application of NIM-76 in rabbits showed no irritation to the vaginal mucosa.

Animals↗
PubMed1990

Development and survival of infective larvae of Haemonchus contortus and Trichostrongylus colubriformis on pasture in a tropical environment.

A trial to determine the seasonal pattern of egg hatching and larval survival on pasture was carried out in representative wet and dry zones of Fiji. Fourteen plots were established on parasite-free pasture at each of two sites. One plot at each site was contaminated every month with faeces from naturally infected goats containing a known proportion of Haemonchus contortus and Trichostrongylus colubriformis eggs. Pasture was sampled at regular intervals after contamination and infective larvae identified and counted. Larvae of both species developed throughout the year in the wet zone but development was more sporadic in the dry zone. Larval counts generally declined to below detectable levels within 9 weeks of contamination between September and March but longevity increased during the cooler weather from April to August. The comparatively short larval survival times noted in this experiment may present opportunities for manipulation of parasite population dynamics in the wet tropics.

Animals↗
PubMed1990

Tumor necrosis factor production by Kupffer cells requires protein kinase C activation.

Tumor necrosis factor (TNF) has been proposed as a primary inflammatory mediator of septic shock. In vitro and in vivo studies indicate that endotoxin- or lipopolysaccharide (LPS)-activated macrophages are a principle source of TNF; however, membrane signal transduction and intracellular pathways by which LPS triggers TNF production in macrophages are unclear. Recent evidence indicates that specific protein phosphorylation via activation of protein kinase C (PKC) is an early, critical step in the signaling of macrophage TNF production by phorbol esters. We hypothesize that PKC activation is also required in LPS-signaled Kupffer cell (KC) TNF production. Murine KCs were obtained by liver perfusion and digestion and then stimulated with LPS (Escherichia coli O111:B4) or LPS in the presence of H-7, a selective PKC inhibitor. Conditioned media was collected at 3 hr for assay of TNF utilizing the L929 cytolysis bioassay standardized to murine-rTNF-alpha. We found that H-7 inhibited significantly LPS signaled TNF release at a concentration of 10 microM, while H-8 (a cyclic nucleotide specific inhibitor) had no effect. The effect of H-7 was dose dependent and present at varying concentrations of LPS. Down regulation of PKC activity by preincubation of KCs with phorbol myristate acetate (PMA, a direct activator of PKC) also resulted in significantly reduced TNF release after LPS stimulation. The inhibitor H-7 (10 microM) also significantly inhibited LPS signaled prostaglandin E2 release in Kupffer cells. Total and specific intracellular protein phosphorylation was determined by trichloroacetic acid precipitation and SDS-polyacrylamide gel electrophoresis after labeling stimulated Kupffer cells with 32Pi. Total protein phosphorylation was not significantly altered by LPS stimulation; however, autoradiograms from PMA- and LPS-stimulated KCs demonstrate enhanced phosphorylation of a 40-kDa protein (2.7 +/- 0.9-fold) and a 33-kDa protein (3.1 +/- 1.0-fold) which were inhibited by H-7. We conclude that activation of PKC and protein phosphorylation are required steps in the signal transduction pathway of LPS-stimulated TNF production in Kupffer cells.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1990

Inhibition of HIV replication by naphthalenemonosulfonic acid derivatives and a bis naphthalenedisulfonic acid compound.

Several naphthalenemonosulfonic acid analogs and a bis naphthalenedisulfonic acid have been evaluated for anti-HIV activity in assays using H9 and MOLT-3 cells. Among the naphthalenemonosulfonic acids, a 4-amino-5-hydroxy compound and a 4,5-diamino compound showed low anti-HIV activity (upto 50% inhibition) at non-toxic doses. The bis naphthalenedisulfonic acid compound demonstrated significant suppression of HIV-1 antigen expression as measured by monoclonal antibodies to p17 (95%), p24 (94%) and syncytia inhibition (82%) at a dose of 20 micrograms/ml that was non-toxic to the host cells. The bis naphthalenedisulfonic acid analog represents a new class of compounds which may be effective in the treatment of HIV infected patients. The structure activity relationship and a probable mode of action of these compounds is discussed.

Antibodies, Monoclonal↗
PubMed1990

Dopaminergic alterations in cotreatments attenuating haloperidol-induced hypersensitivity.

Chronic treatment of the laboratory rat with haloperidol results in an increased stereotypic behavioral response to subsequent dopamine agonist challenge. This behavioral hypersensitivity (BH) is thought to reflect an increase in DA receptor number following chronic pharmacologic denervation. Using a cotreatment strategy, we demonstrate here that a variety of agents can attenuate or prevent the development of BH when administered chronically with haloperidol. Cotreatment with lithium and amantadine prevented the changes in DA biochemistry as well as the proliferation of DA receptors normally associated with chronic haloperidol treatment. Cotreatment with thioridazine or scopolamine did alter the changes in DA biochemistry normally associated with haloperidol treatment, but failed to attenuate the DA receptor proliferation. Taken together, these data suggest that mechanisms in addition to DA biochemical and receptor changes participate in the development and subsequent expression of BH. DA receptor proliferation must, therefore, be considered permissive to the development of BH.

Amantadine↗
PubMed1990

Capping of mammalian U6 small nuclear RNA in vitro is directed by a conserved stem-loop and AUAUAC sequence: conversion of a noncapped RNA into a capped RNA.

The cap structure of U6 small nuclear RNA (snRNA) is gamma-monomethyl phosphate and is distinct from other known RNA cap structures (R. Singh and R. Reddy, Proc. Natl. Acad. Sci. USA 86:8280-8283, 1989). Here we show that the information for capping the U6 snRNA in vitro is within the initial 25 nucleotides of the U6 RNA. The capping determinant in mammalian U6 snRNA is a bipartite element--a phylogenetically conserved stem-loop structure and an AUAUAC sequence, or a part thereof, following this stem-loop. Wild-type capping efficiency was obtained when the AUAUAC motif immediately followed the stem-loop and when the gamma-phosphate of the initiation nucleotide was in close proximity to the capping determinant. Incorporation of a synthetic stem-loop followed by an AUAUAC sequence is sufficient to covert a noncapped heterologous transcript into a capped transcript. Transcripts with the initial 32 nucleotides of Saccharomyces cerevisiae U6 snRNA are accurately capped in HeLa cell extract, indicating that capping machinery from HeLa cells can cap U6 snRNA from an evolutionarily distant eucaryote. The U6-snRNA-specific capping is unusual in that it is RNA sequence dependent, while the capping of mRNAs and other U snRNAs is tightly coupled to transcription and is independent of the RNA sequence.

Base Sequence↗
PubMed1990

Bromocriptine increasingly suppresses the in vitro gonadotropin and alpha-subunit release from pituitary adenomas during long term culture.

Prolonged treatment with bromocriptine may lead to a decrease in tumor size in patients with a gonadotroph, alpha-subunit-secreting, or clinically nonfunctioning pituitary adenoma. The effectiveness of the treatment, however, may depend on its duration. We investigated the effects of prolonged incubation with bromocriptine on the release and intracellular hormone and alpha-subunit concentrations in 10 such adenomas in vitro. The release of FSH, LH, alpha-subunit, or a combination of these was demonstrated in 7 tumors. Bromocriptine significantly suppressed this release in 6 tumors. In 5 tumors bromocriptine had an inhibitory effect on gonadotropin and/or alpha-subunit release which increased with duration of culture. Withdrawal of bromocriptine during the culture period led to a recovery of gonadotropin or alpha-subunit release in the 2 tumors in which it was tested. Intracellular hormone and alpha-subunit concentrations in 3 of 4 tumors cultured for 4 or more weeks were significantly lower in bromocriptine-treated than in untreated cells. We conclude that 1) bromocriptine can suppress the in vitro release of gonadotropins and alpha-subunit from the majority of clinically nonfunctioning, gonadotroph, and alpha-subunit-secreting pituitary adenomas; 2) during prolonged incubation of these tumors with bromocriptine, this drug has a time-dependent increasing inhibitory effect on the release and synthesis of gonadotropins and alpha-subunit, which eventually may lead to decreased intracellular concentrations of these glycoproteins.

Adenoma↗
PubMed1990

Equivalence of five forms of the Selective Reminding Test in young and elderly subjects.

This study evaluated the equivalence of five forms of the Selective Reminding Test, a widely used measure of verbal learning, 45 normal young and 45 normal elderly subjects were randomly administered three of the five test forms on three separate sessions. The five forms generally correlated well with one another and were of comparable difficulty, suggesting adequate test equivalence. Four of the five forms were particularly well matched.

Adolescent↗
PubMed1990

Sucrose metabolism in developing endosperm of immature wheat (Triticum aestivum L.) grain.

With a view to investigating the role of the enzyme pyrophosphate-fructose-6-phosphate-1-phosphotransferase (PFP) in sucrose breakdown in developing endosperm of wheat grain, the activity of PFP and related enzymes such as phosphofructokinase (PFK), fructose-6-bisphosphatase (FBPase), fructose-6-phosphate-2-kinase (PFK-2) and fructose-2,6-bisphosphatase (F2, 6-P2ase) and the contents of the various intermediates of the pathway serving either the substrate or the effectors of these enzymes such as glu-6-P,glu-1-P,fru-6-P,fru-1,6-P2,DHAP,G3P, UDP-glucose, ADP-glucose, Pi,PPi and fru-2,6-P2 have been determined at 5 days intervals starting from day-5 after anthesis until day-40 after anthesis. These enzymes except PFK-2 had their peak activity at day-25 after anthesis. The activity of PFP was several fold higher than that of PFK at each stage of grain development. PFK-2 exhibited the lowest activity. The various intermediates again had their maximum concentration either at day-20 or day-25 after anthesis. Among hexose phosphates studied, glu-6-P was present in highest concentration at each stage of grain development. The level of Pi was much higher than those of PPi and fru-2,6-P2. Similarly, concentration of UDP-glucose was higher than that of ADP-glucose. Based on these results, it is proposed that the major role of the enzyme PFP in developing wheat grain is to provide PPi for sucrose breakdown via sucrose synthase.

Phosphotransferases↗
PubMed1990

Occult carcinoma esophagus metastatic to spine producing paraplegia--a case report and review of literature.

An extremely rare case of asymptomatic squamous cell carcinoma of the esophagus metastatic to the spine leading to paraplegia is reported. The rarity of such an event signifies the relationship between hypercalcaemia and carcinoma of the esophagus. Its occurrence as a second silent primary neoplasm and its association with a negative esophagogram is highlighted.

Carcinoma, Squamous Cell↗
PubMed1990

Serum magnesium levels in chronic renal failure. Clinical significance and correlation with sodium potassium and calcium.

Fifty cases with chronic renal failure and 25 age and sex matched normal healthy controls were studied. The mean serum magnesium level was significantly higher (4.10 +/- 0.85 mg/dl) in the patients as compared to controls (2.40 +/- 0.14 mg/dl; p less than 0.001) and levels rose progressively with deterioration in renal function. Significantly higher serum magnesium levels were observed in patients of chronic renal failure with encephalopathy than in those without. Greater the impairment in level of consciousness, higher was the magnesium level. Improvement in neurological status correlated well with fall in serum magnesium level. The fall was significantly higher in patients on dialysis as compared to non-dialysed patients. Serum magnesium is a worthwhile tool in assessing duration of disease, morbidity and mortality in patients with chronic renal failure. Its estimation may help in evaluating conservative treatment and dialysis in chronic renal failure.

Adult↗
PubMed1990

Duodeno--jejunal vascular malformation.

Vascular malformations are rare but an important cause of obscure upper gastrointestinal bleeding. A patient with a large vascular malformation involving the duodenum and proximal jejunum, presenting with a severe bout of melaena, is described. The diagnosis was suspected on endoscopy and confirmed by angiography and surgery.

Adult↗
PubMed1990

Sarcoidosis masquerading as leprosy, pulmonary tuberculosis and urolithiasis.

A middle aged man presented as a recalcitrant case of borderline leprosy with concomitant pulmonary tuberculosis and urolithiasis which continued to progress relentlessly despite adequate multiduring antileprosy and antitubercular treatment. After detailed and relevant workup, the diagnosis of sarcoidosis was made. Rapid clinical improvement occurred with steroid therapy.

Adult↗