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Biomedical subjects

R Natarajan

Publications and source records attributed to R Natarajan.

At least 19 recordsLinked to original sources
PubMed1992

Vascular smooth muscle cells exhibit increased growth in response to elevated glucose.

Diabetes mellitus is associated with an increased risk of cardiovascular disease. In order to elucidate the association between hyperglycemia and vascular complications, the growth patterns of vascular smooth muscle cells were studied under high glucose conditions. We examined the effect of culturing porcine aortic smooth muscle cells (PVSMC) in high glucose (25 mM, HG) on total cell protein, cell volume, DNA synthesis and cell number. We observed that cells cultured in HG had higher total cell protein content which was associated with increased cell volume as compared to the cells cultured under normoglycemic conditions (5.5 mM glucose, NG). PVSMC cultured in HG also had 1.4 fold increased growth rate and a greater fetal calf serum-induced DNA synthesis rate compared to cells cultured in NG. These observations suggest for the first time that elevated glucose could lead to both hypertrophic and hyperplastic effects in PVSMC. We also examined protein kinase C (PKC) activities as well as the cellular levels of the 12-lipoxygenase product, 12-hydroxyeicosatetraenoic acid (12-HETE) in NG and HG as possible mechanisms for the enhanced growth effects in HG. The results show that PVSMC cultured in HG have increased PKC activity as well as increased levels of 12-HETE. Therefore hyperglycemia may be linked to accelerated vascular disease by increasing smooth muscle cell growth and proliferation.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1992

Leiomyosarcoma of the orbit: diagnosis of its recurrence by fine-needle aspiration cytology.

An 8 1/2-yr-old boy with proptosis was diagnosed to have low-grade leiomyosarcoma of the orbit following lateral orbitotomy and histology of an incompletely excised intraconal mass. He received chemotherapy but had recurrence of proptosis at the age of 12 yr. Ultrasonography revealed a solid mass and its fine-needle aspiration cytology features were consistent with recurrence of leiomyosarcoma. A year later, the cytodiagnosis was confirmed by histology of the excised tumor from a second lateral orbitotomy. Masson's trichrome stain confirmed the smooth muscle nature of the neoplasm and ultrastructural features were in favor of leiomyosarcoma. The patient received intermittent chemotherapy, and is clinically free from disease at the age of 17 yr.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1992

Platelet-derived growth factor is a potent inhibitor of angiotensin II-induced aldosterone synthesis.

Platelet-derived growth factor (PDGF) is a potent mitogen for several cell types. In addition, PDGF has vasoconstrictive action and shares some signal transduction mechanisms with angiotensin II (AII). In the present study, we have examined the effects of PDGF on basal and AII-induced aldosterone synthesis in freshly isolated rat adrenal glomerulosa cells. Recombinant human PDGF-BB caused a dose-dependent inhibition of AII-induced aldosterone synthesis being effective at concentrations as low as 10(-12) M. We also investigated possible mechanisms of action of PDGF. We have previously reported that the 12-lipoxygenase (LO) pathway of arachidonic acid plays a key role in AII-induced aldosterone synthesis. We thus examined whether PDGF action is mediated by changes in 12-LO activation. PDGF, at the same doses that blocked AII-induced synthesis also significantly inhibited AII-induced increases in the 12-LO product, 12-hydroxyeicosatetraenoic acid (12-HETE) formation. Further, the addition of 12-HETE completely restored the stimulatory effect of AII during inhibition by PDGF. These results suggest that PDGF could act, at least in part, by inhibition of AII-induced 12-HETE formation. We also examined the role of diacylglycerol (DG) formation since we have previously reported that DG is the source of arachidonic acid for 12-HETE formation. We observed that both AII and PDGF stimulated [3H]arachidonic acid-labeled DG formation. However, PDGF did not alter AII-induced DG formation suggesting that PDGF action is not mediated by affecting AII-induced increases in DG.(ABSTRACT TRUNCATED AT 250 WORDS)

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1992

Angiotensin II regulates cytochrome P-450 steroid hydroxylase enzyme expression in human adrenal glomerulosa cells.

We have examined the regulation of cytochrome P-450 side chain cleavage enzyme (P-450SCC) and P-45011 beta (18) hydroxylase (P-450(11) beta) enzyme expression by angiotensin II (AII), the major regulator of aldosterone biosynthesis, in cultured human adrenal glomerulosa cells. We also examined the effect of lipoxygenase products of arachidonic acid on the expression of these enzymes since it has been previously shown that the 12-lipoxygenase pathway plays a key role in AII-induced aldosterone synthesis in rat and human adrenal glomerulosa cells. AII (10(-7) mol/L) induced a 3-fold stimulation of P-450SCC and over a 2-fold increase in P-450(11) beta protein expression. The 12-lipoxygenase product, 12-hydroxyeicosatetraenoic acid (12-HETE) caused a 2-fold increase in P-450(11) beta levels without altering P-450SCC levels. These results show for the first time that AII can directly increase the levels of P-450SCC and P-450(11) beta enzymes in glomerulosa cells. The results also suggest that 12-HETE may mediate long term effects of AII action by stimulating P-450(11) beta levels.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1992

Mechanism of angiotensin II-induced proliferation in bovine adrenocortical cells.

The peptide hormone angiotensin-II (AII) is a potent vasoconstrictor and major regulator of aldosterone synthesis. In addition, AII also has growth-promoting effects. We have recently shown that the lipoxygenase (LO) pathway of arachidonic acid plays a major role in AII-induced aldosterone synthesis in adrenal glomerulosa cells. The LO pathway is also involved in the vasopressor and renin-inhibitory effects of AII. However, the role of LO products in AII-induced mitogenic effects have not yet been investigated. In the present studies we have evaluated the role of the LO pathway in AII-induced proliferative responses in a bovine adrenocortical cell clone termed AC1 cells. In addition, the potential receptor type and mechanism of AII-induced proliferation was studied by evaluating the effect of specific nonpeptide type 1 and type 2 AII receptor antagonists and the role of protein kinase-C (PKC). AII-induced DNA synthesis was significantly attenuated by two structurally dissimilar LO inhibitors, baicalein and phenidone. In addition, the LO product 12-hydroxyeicosatetraenoic acid (12-HETE) itself caused a significant increase in DNA synthesis, suggesting that the 12-LO pathway in part plays a role in AII-mediated mitogenesis. AII-induced proliferative responses were blocked by the type 1 AII receptor antagonist. Both AII- and 12-HETE-induced increases in DNA synthesis were markedly inhibited by two PKC blockers, staurosporine and sangivamycin. Further, both AII and 12-HETE could activate PKC by translocating it from the cytosol to the membrane fraction, as determined by Western immunoblotting. These results suggest that both 12-LO activation and protein kinase-C have an important role in AII-induced adrenal cell proliferation.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1991

Glucose induces lipid peroxidation and inactivation of membrane-associated ion-transport enzymes in human erythrocytes in vivo and in vitro.

Erythrocytes of diabetic subjects (non-insulin dependent) were found to have eight- to ten-fold higher levels of endogenously formed thiobarbituric acid reactive malonyldialdehyde (MDA), thirteen-fold higher levels of phospholipid-MDA adduct, 15-20% reduced Na(+)-K(+)-ATPase activity with unchanged Ca+2-ATPase activity, as compared with the erythrocytes from normal healthy individuals. Incubation of normal erythrocytes with elevated concentrations (15-35 mM) of glucose, similar to that present in diabetic plasma, led to the increased lipid peroxidation, phospholipid-MDA adduct formation, reduction of Na(+)-K(+)-ATPase (25-50%) and Ca+2-ATPase (50%) activities. 2-doxy-glucose was 80% as effective as glucose in the lipid peroxidation and lipid adduct formation. However, other sugars, such as fructose, galactose, mannose, fucose, glucosamine and 3-O-methylmannoside, and sucrose, tested at a concentration of 35 mM, resulted in reduced (20-30%) lipid peroxidation without the formation of lipid-MDA adduct. Kinetic studies show that reductions in Na(+)-K(+)-ATPase and Ca+2-ATPase activities precede the lipid peroxidation as the enzyme inactivation occur within 30 min of incubation of erythrocytes with high concentration (15-35 mM) of glucose, while lipid peroxidation product, MDA appears at 4 hr and lipid-MDA adducts at 8 hr. The lipoxygenase pathway inhibitors, 5,8,11-eicosatriynoic acid and Baicalein (5,6,7-trihydroxyflavone), reduced the glucose-induced lipid peroxidation by 30% and MDA-lipid adduct formation by 26%. Indomethacin, a cyclooxygenase pathway inhibitor, had no discernible effect on the lipid peroxidation in erythrocytes. However, the inhibitors of lipid peroxidation, 3-phenylpyrazolidone, metyrapone, and the inhibitors of lipoxygenase pathways did not ablate the glucose-induced reduction of Na(+)-K(+)-ATPase and Ca+2-ATPase activities in erythrocytes. Erythrocytes produce 15-HETE (15-hydroxy-eicosatetraenoic acid), which is augmented by glucose. These results suggest that the formation of lipoxygenase metabolites potentiate the glucose-induced lipid peroxidation and that the inactivation of Na(+)-K(+)-ATPase and Ca+2-ATPase occurs as a result of non-covalent interaction of glucose with these enzymes.

Adenosine Triphosphatases↗
PubMed1991

A herpes simplex virus type 1 mutant lacking the ICP0 introns reactivates with normal efficiency.

Previous evidence suggests that the latency-associated transcript (LAT) gene of herpes simplex virus type 1 appears to have a role during reactivation of latent virus because viruses which are null mutants in this gene reactivate slowly or less efficiently than wild-type viruses. Mapping studies have shown that the LAT gene covers a region of about 8.5 kb that overlaps the ICP0 gene in the repeat long region of the herpes simplex virus genome. Previously, we had constructed a mutant with a deletion in the region of the LAT gene encoding a stable 2-kb RNA species (that accumulates to high levels in latently infected cells) and had shown that it reactivates normally (T.M. Block, J.G. Spivack, I. Steiner, S. Deshmane, M.T. McIntosh, R.P. Lirette, and N.W. Fraser, J. Virol. 64:3417-3426, 1990). We now show that a mutant which has two deletions downstream of this region (deleted in both ICP0 introns) reactivates normally in explant cocultivation assays. Thus, the slow or inefficient reactivation phenotype of herpes simplex virus type 1 LAT null mutants is not assignable to this region of the LAT gene.

Animals↗
PubMed1991

Angiotensin II-induced aldosterone synthesis is potentiated by epidermal growth factor.

Epidermal growth factor (EGF) is a potent mitogen and has effects in several endocrine systems. We examined the effects of EGF on basal and angiotensin II (AII)-induced aldosterone synthesis in freshly isolated rat and cultured human adrenal glomerulosa cells. EGF alone caused a significant increase in basal aldosterone synthesis in both the rat and human cells. In addition, EGF caused a significant increase in AII-induced aldosterone secretion in both rat and cultured human cells during short and long term incubations. Further, we observed that the effect of EGF was highly specific to AII since it did not alter either potassium (8.7 mM) or ACTH (10(-10) M) mediated increases in aldosterone synthesis. We also investigated possible mechanisms of action of EGF. Since earlier studies showed that the lipoxygenase pathway of arachidonic acid plays a key role in mediating AII-induced aldosterone synthesis, we studied the effect of lipoxygenase inhibition in EGF action. We observed that the nonselective lipoxygenase blocker BW755c, which blocked AII-induced aldosterone synthesis, also inhibited EGF mediated increase in aldosterone synthesis. We also examined the effects of EGF on diacylglycerol (DG) formation since DG is an important second messenger in AII action. We found that EGF stimulated basal DG levels and also potentiated AII-induced DG formation, suggesting that EGF may potentiate AII-induced aldosterone synthesis via increases in DG. These results suggest that EGF may play an important role in aldosterone synthesis by acting as a specific positive modulator of AII action in the adrenal.

Adrenocorticotropic Hormone↗
PubMed1991

The product of the CYP11B2 gene is required for aldosterone biosynthesis in the human adrenal cortex.

The steroid 11 beta-hydroxylase (P450c11) enzyme is responsible for the conversion of 11-deoxycortisol to cortisol in the zona fasciculata of the adrenal cortex. Animal studies have suggested that this enzyme or a closely related isozyme is also responsible for the successive 11 beta- and 18-hydroxylation and 18-oxidation of deoxycorticosterone required for aldosterone synthesis in the zona glomerulosa. There are two distinct 11 beta-hydroxylase genes in man, CYP11B1 and CYP11B2, which are predicted to encode proteins with 93% amino acid identity. We used a sensitive assay based on the polymerase chain reaction to analyze the expression of the CYP11B1 and B2 genes. Transcripts of CYP11B1 were detected at high levels in surgical specimens of normal adrenals and also in an aldosterone-secreting adrenal tumor. Transcripts of CYP11B2 were found at low levels in normal adrenals, but at a much higher level in the aldosterone-secreting tumor. CYP11B2 mRNA levels were increased in cultured zona glomerulosa cells by physiological levels of angiotensin-II. The entire coding regions of both CYP11B1 and B2 cDNAs were cloned from the tumor mRNA. Expression of these cDNAs in cultured COS-1 cells demonstrated that the CYP11B1 product could only 11 beta-hydroxylate 11-deoxycortisol or deoxycorticosterone, whereas the CYP11B2 product could also 18-hydroxylate cortisol or corticosterone. A small amount of aldosterone was synthesized from deoxycorticosterone only in cells expressing CYP11B2 cDNA. These data demonstrate that the product of CYP11B2 is required for the final steps in the synthesis of aldosterone.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1991

A review of the molecular mechanism of HSV-1 latency.

The neurotropic herpes viruses, as typified by herpes simplex virus type 1, are noted for their ability to form latent infections. The latent infection differs from the acute infection both in gene expression and the physical state of the viral genome. Latency can be divided into several stages--establishment, maintenance of reactivation--each of which are active areas of research. This review describes the molecular biology of HSV-1 latency and presents the current level of understanding of the molecular mechanism of HSV-1 latency.

Animals↗
PubMed1991

Detection of cryptosporidium oocysts in acute diarrheal stools.

Three hundred and fifty stool samples from patients with acute diarrhea and 30 samples from normal healthy controls were examined for the presence of various parasitic and bacterial enteropathogens by conventional techniques. Cryptosporidium oocysts were detected in 15 out of 350 (4.3%) fecal samples. In 10 cases (2.9%) it was identified as a sole pathogen while in 5 cases (1.4%) it was isolated in association with cysts of E. histolytica, Giardia lamblia and with Salmonella typhimurium. Ten out of fifteen cases were in the pediatric age group. None of the 30 control cases had Cryptosporidium oocysts in their stools.

Acute Disease↗
PubMed1991

Direct estimation of absolute glomerular filtration rate from dynamic renal scintigraphy using gamma camera.

Absolute glomerular filtration rate (GFR), which can serve as a useful parameter of renal function, is not applied in clinical practice due to various technical constraints. We estimated GFR in 20 subjects (10 controls, 10 patients) by two different techniques simultaneously with a single intravenous injection of TC99m DTPA. The GFR results obtained by a conventional plasma clearance technique were compared with that of a simpler, scintigraphic technique which does not require any blood or urine sample, and these were found to correlate significantly (r = 0.75, p less than 0.001). The linear relationship between the fraction of the dose injected taken up by the kidneys during the parenchymal phase of the dynamic imaging study and the overall plasma clearance was also found to be significant (r = 0.932, p less than 0.001) our study shows that reliable estimation of absolute GFR is possible from the routine dynamic renal scinti-scanning procedure using the gamma camera - computer system, and hence might prove applicable in clinical practice.

Adult↗
PubMed1990

Key role of diacylglycerol-mediated 12-lipoxygenase product formation in angiotensin II-induced aldosterone synthesis.

We have shown earlier that the 12-lipoxygenase product of arachidonic acid (AA), 12-hydroxyeicosatetraenoic acid (12-HETE), plays an important role in mediating angiotensin II (AII)-induced aldosterone secretion (J. Clin. Invest. (1987) 80, 1763). In the present study, we have evaluated whether diacylglycerol (DG) is the source of arachidonic acid giving rise to this 12-HETE. Treatment of rat adrenal glomerulosa cells with a DG lipase inhibitor, RHC 80267, which prevents conversion of DG to AA and HETEs, blocked AII-induced aldosterone and 12-HETE formation. In contrast, a DG kinase inhibitor, R59022, which prevents conversion of DG to phosphatidic acid, potentiated AII-induced aldosterone and 12-HETE formation. These two inhibitors block DG metabolism which would be expected to lead to increased DG levels and protein kinase C activity and AII-induced steroidogenesis. However, only R59022 potentiated AII action while RHC 80267 was inhibitory. This suggests that conversion of DG to AA and 12-HETE is important for AII action. Further proof for this was obtained by measuring [3H]AA-labeled DG levels. The combination of the inhibitors significantly potentiated AII-induced DG formation even though this same combination was inhibitory on AII-induced aldosterone and 12-HETE. Thus, the inhibitory effect of RHC 80267 is due to blockade of AA release and not of DG formation. These results suggest that DG plays a dual role in AII action, both as an activator of protein kinase C and as a source of AA for 12-HETE formation.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1990

Complement components in neonatal sepsis.

Complement components C3, C1q, factor B and breakdown products of C3, i.e. C3c and C3d, were evaluated in the diagnosis and prognosis of sepsis in 24 neonates with proven sepsis. The complement components were measured by electroimmunodiffusion and breakdown products by counterimmunoelectrophoresis (CIEP). The babies with sepsis were found to have decreased levels of C1q and factor B as compared with suitably matched healthy controls. No statistically significant depression was observed in C3 levels of infected babies. However, breakdown products of C3, i.e. C3c and C3d, were detected in 58.3% of these babies. The breakdown products of C3 were not present in any of the healthy controls. The degree of depression of complement components was of no prognostic significance in neonatal sepsis.

Bacterial Infections↗
PubMed1989

Diagnosis of retinoblastoma by fine-needle aspiration and aqueous cytology.

This article reports the cytodiagnosis of three cases of retinoblastoma in children aged 1.5, 2.5, and 5 yr. Two of them were diagnosed by fine-needle aspiration cytology of the primary tumor and one by aqueous cytology. The tumor cells were usually round to oval, small and uniform, with scanty cytoplasm; they generally occurred in closely packed clusters of variable sizes. We discuss the differential diagnosis of retinoblastoma with other round-cell tumors of childhood involving the orbit.

Biopsy, Needle↗
PubMed1989

Selective inhibition of angiotensin II-mediated vasoconstriction by lipoxygenase blockade.

We have previously demonstrated that the lipoxygenase (LO) pathway has a specific role in the effect of angiotensin II (ANG II) on aldosterone secretion. To elucidate whether the LO pathway also participates in the vascular effects of ANG II, the nonselective LO inhibitor phenidone (PHE; 30 mg/kg) was administered to rats 1 h before graded dose ANG II infusion. PHE reduced the LO product 12-hydroxyeicosatetraenoic acid (12-HETE) in deendothelialized aortas by an average of 36% as determined by radiometric detection with high-performance liquid chromatography and radioimmunoassay methods. In parallel, the peak systolic pressor response to ANG II was lowered from 36.2 +/- 3.7 to 16.8 +/- 2.0 mmHg. The peak pressor responses to ANG II were also reduced by two other LO inhibitors, baicalein (30 mg/kg) and esculetin (60 mg/kg) (13.9 +/- 2.4 and 22.1 +/- 4.7 mmHg, respectively; P less than 0.01 compared with control rats for both), but not by the cyclooxygenase inhibitor indomethacin. The LO inhibitors baicalein (7.5 X 10(-5) M) and PHE (10(-4) M) markedly attenuated the in vitro contractile response to ANG II of femoral artery rings. In contrast, neither the in vivo nor in vitro constrictor responses to norepinephrine were affected by baicalein. Thus lipoxygenase blockade induces a direct and selective inhibition of ANG II-induced vasoconstriction. The LO pathway may have an important role in mediating the pressor effect of ANG II.

Angiotensin II↗