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Biomedical subjects

G Srinivasan

Publications and source records attributed to G Srinivasan.

At least 19 recordsLinked to original sources
PubMed1997

Blockade of nitric oxide synthesis reduces myocardial oxygen consumption in vivo.

BACKGROUND: Although cardiac myocytes and coronary vascular endothelium are known to express a constitutive form of NO synthase, the in vivo effects of tonic endogenous production of NO on myocardial O2 consumption and contractile performance remain unclear. METHODS AND RESULTS: The effects of blockade of NO synthase were determined in intact dogs. Myocardial O2 consumption decreased systematically over a wide range of hemodynamic demand after the systemic administration of N omega-nitro-L-arginine methyl ester (L-NAME) or N omega-nitro-L-arginine. Decreases after doses of 1 and 10 mg/kg L-NAME averaged 23 +/- 3.8% and 34 +/- 7.2% at a heart rate of 90 bpm in open-chest animals. Similar reductions occurred after the administration of L-NAME and N omega-nitro-L-arginine in chronically instrumented animals and were unaffected by beta-adrenergic blockade. Intracoronary infusion of L-NAME in chronically instrumented animals reduced both myocardial O2 consumption and regional segment shortening, even at a dose that did not increase systemic arterial pressure. CONCLUSIONS: The blockade of NO synthesis reduces myocardial O2 consumption in vivo. The decrease in O2 consumption is accompanied by a decrease in segment shortening. It involves a direct myocardial action of NO, is unaffected by beta-blockade, and is consistent with in vitro studies indicating that low levels of NO augment contractile performance by inhibition of a cGMP-dependent phosphodiesterase.

Animals↗
PubMed1997

Unsuspected vasculitis and intracranial hemorrhage following thrombolysis.

Treatment with thrombolytic agents such as streptokinase or tissue plasminogen activator (TPA) is an accepted standard for the treatment of patients with acute myocardial infarction (MI). A devastating sequel of thrombolytic therapy may be the development of a hemorrhagic complication, particularly intracranial bleeding, which, although rare, is usually associated with significant neurologic sequelae or death. While various risk factors have been correlated with the development of intracranial hemorrhage following thrombolysis, a possible relationship between bleeding and a clinically unsuspected underlying vasculitis has not been previously reported. This report deals with the case of a 49-year-old man who died of multiple intracranial hemorrhages after thrombolytic therapy for acute MI and who was found at autopsy to have had polyarteritis nodosa of the coronary arteries and vasculitis of the meningeal vessels.

Cerebral Hemorrhage↗
PubMed1997

Optimal ligand binding by the recombinant human glucocorticoid receptor and assembly of the receptor complex with heat shock protein 90 correlate with high intracellular ATP levels in Spodoptera frugiperda cells.

The full-length human glucocorticoid receptor (hGR), overexpressed in Spodoptera frugiperda (Sf9) cells, associates with heat shock protein 90 (hsp90) and hsp70 and binds dexamethasone with high affinity. Baculovirus infection of Sf9 cells grown in TNM-FH medium results in the rapid depletion of glucose from the medium within 24 h. Noting a discrepancy between hGR protein levels and ligand binding capacity in such cultures, we hypothesized that the depletion of glucose from the medium could result in intracellular ATP depletion and consequently affect the ligand binding capacity of the recombinant hGR. Supplementation of the Sf9 culture medium with additional glucose resulted in a three-fold increase in intracellular ATP levels, and a three-fold increase in 3H-dexamethasone binding capacity, without altering the protein levels of hGR, hsp90 or hsp70. However, more hsp90 co-immunoprecipitated with hGR from cells grown in glucose supplemented medium. Our data support the hypothesis that high-affinity ligand binding by hGR requires the ATP-dependent formation of the hGR:hsp90 heterocomplex. Besides having practical consequences for the production of recombinant GR and other related proteins, our findings could ultimately have relevance in diseases such as diabetes mellitus.

Adenosine Triphosphate↗
PubMed1996

Evidence for Widespread 26Al in the Solar Nebula and Constraints for Nebula Time Scales

A search was made for 26Mg (26Mg*) from the decay of 26Al (half-life = 0.73 million years) in Al-rich objects from unequilibrated ordinary chondrites. Two Ca-Al-rich inclusions (CAIs) and two Al-rich chondrules (not CAIs) were found that contained 26Al when they formed. Internal isochrons for the CAIs yielded an initial 26Al/27Al ratio [(26Al/27Al)0] of 5 x 10(-5), indistinguishable from most CAIs in carbonaceous chondrites. This result shows that CAIs with this level of 26Al are present throughout the classes of chondrites and strengthens the notion that 26Al was widespread in the early solar system. The two Al-rich chondrules have lower 26Mg*, corresponding to a (26Al/27Al)0 ratio of approximately 9 x 10(-6). Five other Al-rich chondrules contain no resolvable 26Mg*. If chondrules and CAIs formed from an isotopically homogeneous reservoir, then the chondrules with 26Al must have formed or been last altered approximately2 million years after CAIs formed; the 26Mg*-free chondrules formed >1 to 3 million years later still. Because 26Mg*-containing and 26Mg*-free chondrules are both found in Chainpur, which was not heated to more than approximately400°C, it follows that parent body metamorphism cannot explain the absence of 26Mg* in some of these chondrules. Rather, its absence indicates that the lifetime of the solar nebula over which CAIs and chondrules formed extended over approximately5 million years.

Journal Article↗
PubMed1996

Left ventricular ejection fraction: comparison of results from planar and SPECT gated blood-pool studies.

UNLABELLED: Global ejection fraction (EF) from planar gated blood-pool (GBP) imaging is a widely accepted measure of cardiac function. It has been suggested that planar GBP could be replaced by SPECT. In this article, we compare counts-based global EF measured from SPECT and planar images and investigate reasons for discrepancies between the two. METHODS: Twenty-three subjects were imaged with both planar and SPECT GBP. SPECT short-axis slices were projected to create reprojected images. Reprojected SPECT (rSPECT) images were created in both the true long-axis view and also in a view typical of planar studies (found to be 60 degrees from the true long-axis). Thus, angle of view effects on global EF could be investigated. In addition, we studied the effects of background and attenuation. RESULTS: Long-axis rSPECT EF correlated well with planar EF (r = 0.89) but EF values were significantly higher for rSPECT than for planar (slope = 1.4, intercept = -8 EF units; p < 0.001). We found that background correction may not be necessary with rSPECT, but neither background nor attenuation explained the observed discrepancy between rSPECT and planar EFs. This discrepancy was found to be caused by atrial overlap in the planar image and disappeared when the SPECT slices were reprojected at the same angle of view as the planar images. CONCLUSION: Global EF can be easily measured from rSPECT GBP images. Long-axis rSPECT EFs are, however, greater than planar EFs by a factor of 1.4 because atrial overlap causes a significant drop in planar EF in planar images. These results suggest that (long-axis) rSPECT EFs may be more accurate than planar EFs.

Adult↗
PubMed1995

Androgen, estrogen, and progesterone receptors in normal and aging prostates.

Testicular hormones regulate the growth and development of the prostate. The presence of androgen receptors in prostatic tissue and their importance in the normal development of the prostate has been established. Age-related changes in the hormonal milieu, and perhaps steroid hormone receptor profile, could set in motion pathological changes leading to the onset of benign prostatic hyperplasia (BPH) or prostate cancer which primarily affect older men. The accumulation of dihydrotestosterone with age, the reawakening of the inductive potential of the prostatic stroma, the altered rate of apoptosis with age, and the age-related changes in the ratio of testosterone:estrogen have all been implicated in the etiology of BPH. In addition to androgen receptors, several studies have documented the presence of estrogen and progesterone receptors in BPH and prostate cancer. So far, most studies have focussed on the correlation between the presence/absence of steroid hormone receptors and response to hormonal therapy. The molecular mechanisms by which these steroid hormone receptors regulate the onset or progression of BPH and prostate cancer are not yet clear. The chronological changes in the levels and distribution of steroid hormone receptors in normal prostatic tissue and the effect of such changes on the synthesis of growth factors, growth factor receptors, and oncogenes should be investigated.

Aging↗
PubMed1995

Expression of hemidesmosomes and component proteins is lost by invasive breast cancer cells.

Hemidesmosomes are multiprotein structures that attach basal cells of stratified epithelia to basement membranes. Although normal human breast epithelia are not stratified, we observed expression of electron-dense hemidesmosomes and hemidesmosome protein components by breast epithelial and myoepithelial cells at the basal lamina in vivo. Primary cultured normal human breast epithelial cells also contained hemidesmosomes and component proteins, and could be used as a model for hemidesmosome assembly and regulation. In these cultured cells, hemidesmosome proteins were expressed and localized basally in an unvaried temporal pattern, and electron-dense hemidesmosomes were not seen until the final protein was localized to the cell base. In addition, rate of localization was influenced by confluence, doubling time, and extracellular matrix. Invasive breast cancer cells did not express hemidesmosomes or most of the component proteins in vivo. In carcinoma in situ, cells away from the basement membrane lacked hemidesmosomes and hemidesmosome proteins, and cells at the basement membrane exhibited abnormalities of hemidesmosome protein expression. Primary human malignant breast cells in culture exhibited a mix of hemidesmosome phenotypes. These data suggest that hemidesmosomes may be important subcellular structures in determining the cytoarchitecture of the breast epithelium. Further, their downregulation may influence cytoarchitecture remodeling closely linked with cell cycle, motility, and extracellular matrix interactions; and their loss in carcinoma may be associated with loss of normal cytoarchitecture.

Autoantigens↗
PubMed1994

Heat shock protein is tightly associated with the recombinant human glucocorticoid receptor:glucocorticoid response element complex.

The association of heat shock proteins (hsp) with steroid hormone receptors may have functional significance for steroid receptor action. The association of hsp90 with steroid receptors is thought to maintain the receptors in the nonactivated state until their interaction with the respective ligand. The association of hsp70 with progesterone receptor has been well documented. However, there is evidence both for and against the association of hsp70 with the glucocorticoid receptor (GR). We have examined the interaction between hsp70 and human (h) GR over-expressed in the Baculovirus system. Immunoprecipitation and sucrose gradient centrifugation studies demonstrated the association of hsp70 with both the nonactivated and in vitro activated hGR. We were unable to dissociate hGR and hsp70 by incubation of crude cytosol with 3 mM ATP and 0.5 M NaCl. In vivo activation of hGR did not result in dissociation of hsp70 from hGR. Hsp70 coeluted with hGR from a glucocorticoid response element (GRE)-Sepharose column, suggesting that hsp70 is part of the GRE-hGR complex. Both an anti-hGR antibody and an anti-hsp70 antibody were capable of further retarding the migration of a [32P]GRE-hGR complex in polyacrylamide gels. The in vitro activated hGR has been shown to be highly active in an in vitro transcription system. We speculate that hsp70 may influence the DNA-binding and/or transcriptional activities of hGR.

Base Sequence↗
PubMed1993

Cortivazol increases glucocorticoid receptor expression and inhibits growth of hamster pancreatic cancer (H2T) in vivo.

Glucocorticoids are effective in the treatment of certain leukemias and lymphomas, but their effects on the growth of several solid tumors have not been determined. We report here that cortivazol (CVZ), a potent synthetic glucocorticoid, inhibits the growth of a hamster pancreatic adenocarcinoma, H2T, in vivo. CVZ regulation of glucocorticoid receptor (GR) expression was followed as a specific molecular correlate. H2T cells were injected into cheek pouches of male Syrian golden hamsters, where they formed readily measurable tumors. Two studies were performed. In the first, hamsters were randomized to three groups immediately after injection of tumor cells: control, CVZ (0.1 micrograms/g body wt), or CVZ (0.3 micrograms/g body wt). Injections of either CVZ or its vehicle were administered on a 14-day cycle of 5 treatment days, followed by 9 days off treatment. Tumors were measured and areas calculated weekly. On day 48, the hamsters were killed and the tumors excised, weighed, and analyzed for DNA, RNA, and protein content. In the second study, randomization and treatment schedule were as before, except that on day 33 the hamsters were killed, tumors were excised and weighed, and total RNA from the tumors was isolated. GR mRNA content was determined by filter hybridization with a 32P-labeled GR cDNA probe, and the signal normalized by reprobing for alpha-tubulin as an invariant, independent signal. At either dose, CVZ significantly inhibited H2T tumor area and weight and DNA, RNA, and protein content. Body weights of animals treated with CVZ were not significantly decreased as compared with controls. In addition, GR mRNA in H2T cells was increased approximately twofold by CVZ.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenocarcinoma↗
PubMed1993

Pulmonary arterial elasticity in awake dogs.

We measured the relationship between pulmonary arterial pressure (Ppa), diameter (D), and length of a segment of the main pulmonary artery (MPA) in chronically instrumented conscious dogs breathing spontaneously (CCC). There were no physiologically significant changes in Ppa or D in the CCC dogs postoperatively, and the cross-sectional MPA shape measured by fast computed tomography was nearly circular. These results suggest that the MPA was not distorted by chronic instrumentation. We compared measurements made in the CCC dogs with previous measurements in acutely instrumented anesthetized dogs with open chests (AAO). The elasticity of MPA in the CCC animals was frequency dependent between 1 and 14 Hz and was similar to that in the AAO dogs. Oscillations of D preceded Ppa at cardiac frequencies in the AAO animals, but the D and Ppa oscillations were in phase in the CCC animals. The oscillations of length relative to D were significantly less in the CCC than in the AAO dogs. We conclude that, with limitations, the hemodynamic properties of the MPA can be measured in the CCC subjects. We suggest that the discrepancies between the AAO and CCC dogs can be attributed to differences in extrinsic loading of the MPA.

Animals↗
PubMed1993

Characterization of the human oxysterol receptor overexpressed in the baculovirus system.

Oxysterols are potent regulators of enzymes of the de novo cholesterol biosynthetic pathway and do not require the LDL (low density lipoprotein):LDL receptor system for their regulatory actions. The search for an alternate transduction system led to the identification of an oxysterol binding protein. This cytosolic protein has been extensively characterized, purified, and cloned. Although it fulfills the pharmacologic criteria for an oxysterol receptor by binding to oxysterols with affinities corresponding to their regulatory potencies, its function in maintaining cholesterol homeostasis has not been determined. We have overexpressed the human oxysterol receptor in Spodoptera frugiperda cells using the Baculovirus system. The overexpressed protein binds oxysterols, but not cholesterol. The affinity for 25-hydroxycholesterol determined by competitive binding assay was 7.3 +/- 4.4 nM (mean +/- SD), and the relative affinities of several other oxysterols approximately corresponded to their potencies in cell systems. The expressed protein migrated as a single immunoreactive band on denaturing polyacrylamide gels with a molecular mass of 94 kDa. The molecular mass calculated from sucrose gradient centrifugation and gel filtration was 273 kDa for the 9.8S form, 217 kDa for the 7.8S form, and 184 kDa for the 6.6S form. However, velocity gradient centrifugation and heparin-sepharose chromatography each indicated that there were at least two fractions containing specific oxysterol binding. We conclude that we have successfully overexpressed the human oxysterol receptor and that biochemical analysis of the overexpressed protein provides evidence of interactions with other proteins. Further analysis of the overexpressed protein should provide clues regarding its role in maintaining cholesterol homeostasis.

Animals↗
PubMed1993

Ontogeny of stool passage in low birth weight infants < or = 1500 grams.

The onset of stool passage, timing of transition to yellow stools and the pattern of stooling frequency over the first 4 weeks were studied in infants < 1500 g at birth. The time of passage of the first stool (median, 19) correlated with birth weight and gestational age but not with presence or severity of respiratory distress; fourteen percent passed stool after 1st 48 hours. Transition to yellow occurred at 17.6 +/- 6.4 days and was related to the onset of feeding and birth weight. Stooling frequency was similar in Wk 2 as Wk 1, increased in Wk 3 and plateaued on Wk 4. Volume of feeding/day increased each week over that of preceding week but stooling frequency was not related to the increased volume or any of the other variables.

Birth Weight↗
PubMed1991

Synergism between steroid response and promoter elements during cell-free transcription.

We have analyzed quantitatively the influence of distal promoter elements on steroid-responsive gene expression in vitro. Functional synergism between enhancer and distal promoter elements was examined using two model promoters, one containing a natural promoter (mouse mammary tumor virus long terminal repeat) and one constructed artificially. Human glucocorticoid receptor (GR) expressed in baculovirus induces transcription from a mouse mammary tumor virus long terminal repeat-containing DNA template. Transcription is diminished by oligonucleotides containing a nuclear factor 1 (NF-1)-binding site or a glucocorticoid/progesterone response element. Quantitative analysis indicates that NF-1 and GR act synergistically during transcriptional activation. In contrast, efficient activation by GR or purified chick progesterone receptor of a glucocorticoid/progesterone response element-linked ovalbumin promoter does not require interaction with the chicken ovalbumin upstream promoter (COUP) element in the distal promoter. Lack of synergism is not related to enhancer strength, since the glucocorticoid/progesterone response elements can be moved further from the promoter or reduced to a single copy response element without increasing the dependence upon COUP. Strong synergism is restored following substitution of an NF-1 distal promoter element for the COUP element in this construct. Our results suggest that synergism between steroid response and distal promoter elements is dependent upon the identity of the promoter element rather than upon the inherent strength of the enhancer element.

Animals↗
PubMed1990

Recombinant human glucocorticoid receptor induces transcription of hormone response genes in vitro.

A recombinant full length human glucocorticoid receptor stimulates transcription in vitro of test genes containing synthetic glucocorticoid and progesterone response elements or murine mammary tumor virus promoter. The receptor expressed in a baculoviral vector is highly active, enhancing transcription of hormone response genes greater than 30-fold even at a receptor concentration of 1.2 nM. The enhancement of transcription is glucocorticoid and progesterone response element-dependent, suggesting that it is a receptor mediated event. In vitro and in vivo treatment with the agonist dexamethasone or with the antagonist Ru486 did not alter significantly the functional activity of partially purified receptor. Kinetic studies suggest that both glucocorticoid receptor and HeLa cell extracts are required for formation of a stable committed transcriptional complex. Our results indicate that the action of glucocorticoid receptor on gene transcription is similar to that defined recently for the progesterone receptor and may be a general mechanism for all steroid receptors.

Animals↗
PubMed1990

Overexpression of full-length human glucocorticoid receptor in Spodoptera frugiperda cells using the baculovirus expression vector system.

We have expressed a full-length human glucocorticoid receptor (hGR) in Spodoptera frugiperda (Sf9) cells using the baculovirus expression vector system (BEVS). The level of expression is approximately 100-fold greater than in CEM-C7 cells. Between 0.5-1.0 mg hGR can be generated per liter of Sf9 cell culture. The expressed hGR is capable of binding glucocorticoids with specificity and high affinity. Covalent labeling with 3H-dexamethasone mesylate and Western blot analysis using a polyclonal antibody indicate that the molecular weight of the expressed protein is approximately 94 k. The nonactivated receptor sediments as a 8-9S complex in sucrose gradients and can be heat activated to a 4S form. The activated receptor is capable of retarding the migration of a 23 base-pair DNA fragment containing the glucocorticoid response element from the tyrosine aminotransferase gene. These data indicate that the expressed GR displays characteristics identical to those of GR from mammalian cells. By scaling up this culture we can, for the first time, obtain enough purified full-length receptor for crystallographic and functional studies which could provide new insight into exactly how hGR works.

Animals↗