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Biomedical subjects

G Gupta

Publications and source records attributed to G Gupta.

At least 163 records · Page 9Linked to original sources
PubMed1990

Purification and immunochemical interrelationship of insulin receptors from rat brain and liver.

Insulin receptors from rat brain and liver were purified. Brain purified receptor exhibited protein bands of apparent Mr = 135,000 and 95,000 molecular weight corresponding to alpha- and beta-subunits, retained a tyrosine specific protein kinase activity and demonstrated phosphorylation that is hormonally sensitive. Antisera were raised against both insulin receptor preparations and enzyme-linked immunosorbent assay was developed. The comparison of two insulin receptors was based on a displacement enzyme-linked immunosorbent assay where antisera were interchanged on predetermined optimal dilutions. This indicated that both insulin receptors possess some unique antigenic determinants thereby implying a structural difference.

Animals↗
PubMed1990

Effect of chronic administration of propranolol on acetylcholinesterase and 5-hydroxytryptamine levels in rat brain and heart.

The effect of chronic administration of propranolol on the rat brain and heart acetylcholinesterase was studied by administering propranolol (5mg/kg body weight) for 14 days. This treatment was found to substantially inhibit the enzyme activity. Levels of 5-hydroxytryptamine were measured in the brain and heart; in brain the levels of 5-hydroxytryptamine increased with propranolol administration, while in the heart there was no change. Effect of different concentrations of propranolol on acetylcholinesterase activity was also studied in vitro and a decreased activity of the enzyme was found in brain and heart homogenates. The significance of these results is discussed in terms of the therapeautic effects of the drug in the control of hypertension.

Animals↗
PubMed1990

Rat brain insulin degrading enzyme in insulin and thyroid hormones imbalances.

Rat brain insulin degrading enzyme activity and its relationship with insulin receptor were investigated in experimental hyperglycemia, hyperinsulinemia, hypothyroidism and hyperthyroidism. Insulin degrading enzyme activity was assessed in synaptosomes and high speed cytosol using [125I]insulin. Levels of insulin degrading enzyme were changed in high speed cytosol in insulin and thyroid hormone imbalances. These results suggest that insulin degrading enzyme in brain is predominantly active in cytosol and is subject to regulation by insulin and thyroid hormones. Probably it plays some role in long term effects of insulin in brain.

Animals↗
PubMed1990

Modulation of insulin receptors and catecholamines in rat brain in hyperglycemia and hyperinsulinemia.

Insulin receptor activity and its relationship with catecholamines and serotonin were investigated in rat whole brain membranes, synaptosomes and choroid plexus in alloxan induced short term and long term hyperglycemia and hyperinsulinemia. Insulin receptor activity was measured by [125I]insulin binding and catecholamines by high performance liquid chromatography with electrochemical detection. While choroid plexus insulin receptors modulate along with norepinephrine, dopamine and serotonin with the changes in insulin and/or plasma glucose levels, insulin receptor activity in synaptosomes and total membranes is not affected to a great extent except in long term hyperglycemia.

Alloxan↗
PubMed1990

Effect of hyperglycemia and hyperinsulinemia on rat red blood cell insulin receptors and catecholamines: relationship with cellular ageing.

Insulin receptor activity and its relationship with catecholamines in rat young, middle aged and old red blood cells were investigated in short term (4-6) weeks and long term (6-8 months) hyperglycemia and hyperinsulinemia. Loss of insulin receptor activity is linear with cellular ageing and norepinephrine and epinephrine levels increase with age together with levels of glycosylated hemoglobin in control animals and this correlation is altered in hyperglycemia and hyperinsulinemia. These results suggest that loss of insulin receptor in cellular ageing is probably part of a more generalised alteration which is possibly brought about by glycosylation.

Animals↗
PubMed1989

Studies on mechanism(s) of antifertility action of gossypol in rat and hamster.

This study was undertaken with a view to investigate the possible mechanism(s) of antifertility action of gossypol acetate in rats and hamsters. Adult male rats were treated by gavage with 30 mg/kg/day of gossypol for 7 weeks and adult male hamsters were treated similarly with 20 mg/kg/day gossypol for 8 weeks. The treatment caused a marked reduction in the weights of testis and epididymis. Histological examination of the testis in the two species revealed presence of seminiferous tubules showing varying degrees of damage along with a large number of normal tubules. Exfoliation of germ cells and spermatogenic arrest at spermatid stage was a common feature. Leydig cells presented normal morphological features. Though there was a reduction in the diameter of epididymal tubules, the epithelium did not show any morphological alterations. Examination of vasal flushings revealed marked reduction in sperm population and consisted of decapitated and immotile spermatozoa. Gossypol caused a significant reduction in the levels of total protein, RNA and DNA, and a marginal decrease in glycogen content in the testis. This was accompanied by a reduction in the activities of SDH and MDH. Except for LDH activity which showed a marked rise, there was no effect on glycolytic enzymes in the testis. The concentrations of glycerylphosphorylcholine and sialic acid were reduced in the cauda epididymis. The antifertility effects of gossypol appear to be due to its action both on testis as well as on epididymis.

Animals↗
PubMed1989

Effects of nitrogen dioxide on growth and yield of black turtle bean (Phaseolus vulgaris L.) cv. 'Domino'.

Twenty-six-day-old black turtle bean cv. 'Domino' plants were exposed to nitrogen dioxide (0.0, 0.025, 0.05 and 0.10 microl liter(-1)), 7 h per day for 5 days per week for 3 weeks, under controlled environment. Data were collected on net photosynthesis rate (PN), stomatal resistance (SR), and dark respiration rate (DR), immediately after exposure, 24 h after the termination of exposure and at maturity (when the leaves had just started turning yellow), using a LICOR 6000 Portable Photosynthesis System. Chlorophyll-a (Ch-a), chlorophyll-b (Ch-b), total chlorophyll (tot-Ch) and leaf nitrogen were measured immediately after exposure and at maturity. Growth characteristics-relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR) and root: shoot ratio (RSR)-were computed for treated plants. Net photosynthesis rate increased by 53% in 0.10 microl liter(-1) NO2 treated plants immediately after exposure compared to control plants. Dark respiration rates were also higher in treated plants. Ch-a, Ch-b and tot-Ch showed significant increases with 0.1 microl liter(-1) NO2 treatment immediately after exposure. Foliar nitrogen content showed an increase in treated plants both immediately after exposure and at maturity. Increases were also seen in RGR and NAR. Plant yield increased by 86% (number of pods), 29% (number of seeds) and 46% (weight of seeds), respectively. Nitrogen dioxide stimulated the overall plant growth and crop yield.

Journal Article↗
PubMed1989

Effect of antiandrogens on some key enzymes of glycolysis in epididymis and ventral prostate of rat.

Effect of three antiandrogens: cyproterone acetate (5 mg/day, sc), flutamide (5 mg/day, sc) and STS-557 (5 mg/day, po) and an estrogen, estradiol dipropionate (5 micrograms/day, sc) on some key enzymes of carbohydrate metabolism was investigated in adult rat epididymis and ventral prostate. Antiandrogens were administered for 21 days and estrogen for 14 days. All of them caused a significant decrease in the weight of epididymis, seminal vesicles and ventral prostate. A significant decrease in the specific activities of enzymes (hexokinase, phosphofructokinase, aldolase, glyceraldehyde phosphate dehydrogenase, pyruvate kinase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase) occurred only in the organs of estrogen treated rats; activities of some of the enzymes were lowered also in the prostate of STS-557 treated rats. Flutamide and cyproterone acetate were ineffective in this regard. The possible factors responsible for the ineffectiveness of synthetic antiandrogens in influencing epididymal metabolism are discussed.

Androgen Antagonists↗
PubMed1988

On the question of DNA bending: two-dimensional NMR studies on d(GTTTTAAAAC)2 in solution.

It is very well documented that the presence of an An.Tn tract causes intrinsic DNA bending. Hagerman demonstrated that the sequence in which the An.Tn tracts are joined plays a very crucial role in determining DNA bending. For example, Hagerman showed that the polymer with a repeat of d(GA4T4C)n greater than or equal to 10 is bent but the polymer with a repeat of d(GT4A4C)n greater than or equal to 10 is not bent [Hagerman, P. J. (1986) Nature (London) 326, 720-722]. Earlier we have shown that the decamer repeat d(GA4T4C)2 is itself bent with a finite structural discontinuity at the A----T sequence [Sarma, M. H., Gupta, G., & Sarma, R. H. (1988) Biochemistry 27, 3423-3432]. In the present article, we summarize our studies on the decamer repeat d(GT4A4C)2 structure in solution. By employment of 1D and 2D 1H NMR studies at 500 MHz a complete sequential assignment has been made for the exchangeable and nonexchangeable protons belonging to the ten nucleotides. NOESY data were collected for d(GT4A4C)2 at 17 degrees C in D2O for three mixing times, 150, 100, and 50 ms. A quantitative NOESY simulation technique was employed to arrive at a structural model of d(GT4A4C)2 in solution. Our detailed analyses revealed the following structural features: (i) The duplex adopts the gross morphology of a B-DNA. (ii) All the A.T pairs are propeller twisted (less than or equal to -15 degrees). (iii) Although both A and T nucleotides belong to the C2'-endo,anticonformational domain, there is a mild variation in the actual conformation of the A and T residues. (iv) Even though there is a subtle conformational difference in the A and T nucleotides, two structural frames of T4.A4 segments are joined at the T----A sequence in such a way that there is no finite discontinuity at the junction; i.e., two neighboring frames exactly coincide at the T----A junction. Thus, our studies on d(GA4T4C)2 (Sarma et al., 1988) and on d(GT4A4C)2 (this article) reveal the structural peculiarity of the An.Tn tract and the effect of A----T/T----A sequence in causing DNA bending.

Base Composition↗
PubMed1988

Structure of a bent DNA: two-dimensional NMR studies on d(GAAAATTTTC)2.

Intrinsic DNA bending is caused by specific DNA sequences. The decamer d(GA4T4C)2, when it repeats in a synthetic polymer or in kinetoplast DNA, results in a macroscopic bending of the molecule as a whole. We employed high-resolution two-dimensional NMR methods to examine the intrinsic structural properties of the d(GA4T4C)2 duplex in solution. Examination of the NOESY data at 50- and 100-ms mixing times indicated that the kinds of observed NOEs can originate if each of the ten nucleotidyl residues belongs to the B-DNA family, i.e., C2'-endo,anti. However, the degree of observed NOE intensities from the A-T junction as well as the observed AH2-AH2 cross-peaks from adjacent AT pairs could not be rationalized on the basis of a straight B-DNA model but could be explained by only a B-DNA model with some structural discontinuity at the A-T junction--the site of 2-fold symmetry in the molecule. In view of the fact that the degree of observed NOE intensities can be complicated by spin diffusion and by fine structural distortion, we have resorted to the use of quantitative theoretical NOESY simulation (which takes into account primary, secondary, and higher orders of NOE) to delineate the structural discontinuity at the A-T junction and to arrive at a structure for the duplex d(GA4T4C)2. We propose a "junction B-DNA model" which can quantitatively explain the 2D NOESY data at 100- and 50-ms mixing times. In this model the two structural blocks in the molecule, i.e., d(GA4).d(T4C) and d(T4C).d(GA4), are conformationally equivalent and are connected at the A-T junction where the base pairs are stably stacked, but the two local structural frames do not coincide in space. This model can create an overall bending of 10 degrees with a center of curvature 50 A away from the center of the duplex. It is the thesis of this paper that the observed bending in polymers with a repeat of d(GA4T4C)2 and the bending in natural DNAs where AnTn.AnTn repeats are present originate at the oligonucleotide repeat level.

Base Sequence↗
PubMed1988

Effects of nitrogen dioxide on biochemical and physiological characteristics of soybean.

One month old soybean (Glycine max (L.) Merrill) cv. 'Williams' plants were exposed to nitrogen dioxide (NO2 at 0.1, 0.2, 0.3, and 0.5 microl liter(-1) and carbon filtered air (control), 7 h per day for five days, under controlled environment. Data were collected on net photosynthetic rate (PN), stomatal resistance (SR), and dark respiration rate (DR), immediately following the fifth day of exposure and 24 h after termination of exposure. Chlorophyll a (Ch a), chlorophyll b (Ch b), total chlorophyll (tot Ch) and foliar nitrogen (N) were measured before and after exposures. Growth characteristics--relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), and root shoot ratio (RSR) -- were computed for treated plants using standard growth equations. Increases of 18% and 23% in PN were observed immediately following exposure to 0.2 microl liter(-1) NO2 and after 24 h recovery period, respectively. With 0.5 microl liter(-1) NO2 treatment, reductions in PN of 23% and 50% were observed, immediately after exposure and following 24 h recovery, respectively. DR rates with 0.2 l liter(-1) treatment were higher than the control. Chlorophyll a and tot Ch showed significant reduction with 0.5 microl liter(-1) NO2 treatment. The percent reduction in Ch a and tot Ch with 0.5 microl liter(-1) NO2 were 45% and 47%, respectively. Increases in foliar nitrogen content after 0.2 and 0.3 microl liter(-1) NO2 treatments were 46% and 69%, respectively. Nitrogen dioxide at 0.5 microl liter(-1) reduced RGR and NAR by 47% and 51%, respectively. Leaf area ratio was 42% higher in 0.5 microl liter(-)1 NO2 treated plants, compared with the control; this increase was insufficient to compensate for the decrease in NAR resulting in a net decline in RGR. Nitrogen dioxide up to 0.2 microl liter(-1) increased PN and foliar-N content of soybean. With 0.5 microl liter(-1) NO2, significant decreases were observed in PN, leaf chlorophyll, foliar-N, NAR and RGR. Nitrogen dioxide up to 0.2 microl liter(-)1 has a favorable influence on overall growth characteristics of soybean; however, inhibitory effects were seen with NO2 treatment at 0.5 microl liter(-1).

Journal Article↗
PubMed1988

Effects of nitrogen dioxide on leaf chlorophyll and nitrogen content of soybean.

One-month-old soybean (Glycine max [L.] Merrill), cultivar 'Williams', plants were exposed to nitrogen dioxide (0.1, 0.2, 0.3 and 0.5 ppm) and carbon filtered air (control), 7 h per day, for 5 days, under a controlled environment. Leaf chlorophyll content (Ch a, Ch b, and total Ch content) and foliar nitrogen content (%N) were determined before and after the exposure. The influence of NO(2) treatments up to 0.3 ppm on leaf chlorophyll content was negligible although a stimulatory effect was evident in Ch a and total Ch content with 0.2 ppm NO(2). Marked decline in Ch content was observed with 0.5 ppm treatment; the reductions in Ch a and total Ch were 45% and 47%, respectively. Foliar-N contents of plants treated with 0.2 and 0.3 ppm NO(2) were higher than the control; plants exposed to 0.5 ppm NO(2) showed a 41% reduction in foliar-N compared to pre-exposure values.

Journal Article↗
PubMed1988

Stability and motion of a hairpin and the corresponding mismatched duplex: a theoretical exploration using molecular mechanics and normal mode analysis of 2D NMR results on d(GCCGCAGC).

The oligomer d(GCCGCAGC) can adopt two different conformations: i) a duplex with two mismatched A.C base pairs and ii) a hairpin with two C.G base pairs and a single stranded loop. We report molecular mechanics, normal mode analysis, and thermodynamic stability calculations for both structures. We show that the energy-minimized structure and harmonic-dynamics results are in complete agreement with the observed NOE spectrum and imino proton exchange data. We conclude that the high stability of the hairpin structure over the duplex at low salt concentration is due to the higher vibrational entropy contribution to the system free energy by the single stranded loop and to the lack of minor groove phosphate/phosphate electrostatic repulsions that tend to destabilize the duplex.

Base Composition↗
PubMed1988

Influence of selenium on 3-methylcholanthrene induced skin carcinogenesis in mice.

Incidence of skin papillomas/tumors have been studied in ICRC male mice after surface application of 3-methylcholanthrene (MCA) after selenium treatment. Decrease in percentage incidence and tumor burden was noticed. Also increase in latent period of induction was observed. As no influence of selenium was noticed on arylhydrocarbon-hydroxylase activity in skin and liver, so activation/inactivation of carcinogen is ruled out with selenium treatment. Since there is significant increase in glutathione S-transferase activity with selenium treatment, hence detoxication pathways may be active in suppression of carcinogenic activity with selenium treatment.

Animals↗
PubMed1987

DNA structure in which an adenine-cytosine mismatch pair forms an integral part of the double helix.

Extensive studies using one- and two-dimensional 1H NMR at 500 MHz revealed that the oligonucleotide d(CGCCGCAGC) in solution at 5 degrees C forms a double helix under conditions of high salt (500 mM in NaCl, 1 mM sodium phosphate), low pH (pH 4.5), and high DNA concentration (4 mM in duplex). The presence of very strong nuclear Overhauser effects (NOEs) from base H8/H6 to sugar H2',H2" and the absence of NOE from base H8/H6 to sugar H3' suggested that the oligomer under these solution conditions forms a right-handed B-DNA double helix. The following lines of experimental evidence were used to conclude that C4 and A7 form an integral part of the duplex: (i) the presence of a NOESY cross-peak involving H8 of A7 and H8 of G8, (ii) the presence of a two-dimensional NOE (NOESY) cross-peak between H6 of C3 and H6 of C4, (iii) base protons belonging to C4 and A7 forming a part of the H8/H6---H1' cross-connectivity route, and (iv) the pattern of H8/H6---H2',H2" NOESY cross-connectivity based upon a B-DNA model requiring that both C4 and A7 form an integral part of the duplex. The possibility of an A-C pair involving H bonds was also examined. Two possible structural models of the duplex at pH 4.5 are proposed: in one model A-C pairing involves two H bonds, and in the other A-C pairing involves a single H bond.

Adenosine↗
PubMed1987

DNA hairpin structures in solution: 500-MHz two-dimensional 1H NMR studies on d(CGCCGCAGC) and d(CGCCGTAGC).

A hairpin structure contains two conformationally distinct domains: a double-helical stem with Watson-Crick base pairs and a single-stranded loop that connects the two arms of the stem. By extensive 1D and 2D 500-MHz 1H NMR studies in H2O and D2O, it has been demonstrated that the DNA oligomers d(CGCCGCAGC) and d(CGCCGTAGC) form hairpin structures under conditions of low concentration, 0.5 mM in DNA strand, and low salt (20 mM NaCl, pH 7). From examination of the nuclear Overhauser effect (NOE) between base protons H8/H6 and sugar protons H1' and H2'/H2", it was concluded that in d(CGCCGCAGC) and d(CGCCGTAGC) all the nine nucleotides display average (C2'-endo,anti) geometry. The NMR data in conjunction with molecular model building and solvent accessibility studies were used to derive a working model for the hairpins.

DNA↗