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Biomedical subjects

R Singh

Publications and source records attributed to R Singh.

At least 613 records · Page 34Linked to original sources
PubMed1986

A test of the bay-region mechanism in carcinogenesis for monomethyl benz[a]anthracenes in a self-consistent-field molecular orbital theory.

The relative carcinogenic activity of the isomeric monomethyl derivatives of benz[a]anthracene has been studied on the basis of their bay-region reactivity, and the subsequent ease of carbonium ion formation, as obtained from a suitable 'self-consistent-field' molecular orbital theory for the mobile pi-electrons. The predicted order of carcinogenic activity of these molecules is compared with the available experimental data.

Benz(a)Anthracenes↗
PubMed1986

Purification and Properties of Phosphoenolpyruvate Carboxylase from Immature Pods of Chickpea (Cicer arietinum L.).

Phosphoenolpyruvate carboxylase (EC 4.1.1.31) was purified to homogeneity with about 29% recovery from immature pods of chickpea using ammonium sulfate fractionation, DEAE-cellulose chromatography, and gel filtration through Sephadex G-200. The purified enzyme with molecular weight of about 200,000 daltons was a tetramer of four identical subunits and exhibited maximum activity at pH 8.1. Mg(2+) ions were specifically required for the enzyme activity. The enzyme showed typical hyperbolic kinetics with phosphoenolpyruvate with a K(m) of 0.74 millimolar, whereas sigmoidal response was observed with increasing concentrations of HCO(3) (-) with S(0.5) value as 7.6 millimolar. The enzyme was activated by inorganic phosphate and phosphate esters like glucose-6-phosphate, alpha-glycerophosphate, 3-phosphoglyceric acid, and fructose-1,6-bisphosphate, and inhibited by nucleotide triphosphates, organic acids, and divalent cations Ca(2+) and Mn(2+). Oxaloacetate and malate inhibited the enzyme noncompetitively. Glucose-6-phosphate reversed the inhibitory effects of oxaloacetate and malate.

Journal Article↗
PubMed1986

The effects of norethisterone in postmenopausal women on oestrogen replacement therapy: a model for the premenstrual syndrome.

The influence of norethisterone on mood and behaviour was investigated in prospective placebo-controlled study in 58 postmenopausal hysterectomized women who were being treated with subcutaneous oestradiol and testosterone implants. Norethisterone, 2.5 or 5 mg daily, was given for 7 days and a placebo for two periods of 7 days. Psychological, behavioural and physical variables were assessed using the Menstrual Distress Questionnaire. There were widespread adverse effects which were dose-related. Significant changes in five of the eight symptom complexes studied (pain, concentration, behavioural change, water retention and negative affect) were found with 5 mg/day of the progestogen. The symptoms were similar to the typical complaints of the premenstrual syndrome, such that a combination of oestradiol and testosterone implants with cyclical oral norethisterone appears to be a model for this condition. The dose of this progestogen should therefore be the minimum to achieve the desired therapeutic effect.

Adult↗
PubMed1986

Genetic studies of Pangwalas, Transhumant and Settled Gaddis. 4. Colour blindness, mid-phalangeal hair, ear lobe attachment and behavioural traits.

Frequency distributions of colour blindness, midphalangeal hair, ear lobe attachment, hand clasping, arm folding, leg folding and handedness are reported for different population groups from Himachal Pradesh, North India, namely Pangwalas, Transhumant Gaddis (Brahmans, Rajputs and Scheduled Castes) and Settled Gaddis (Brahmans, Rajputs and Schedules Castes). An attempt has been made to compare the results of the present study within and between these groups as well as with the results of other reports from different population groups of India and Asia.

Color Vision Defects↗
PubMed1986

Studies on calcium homeostasis in the fetal Yucatan miniature pig.

Along with parallel studies with a conventional breed of pig, the Yucatan breed has been investigated for studies on the mechanisms of calcium homeostasis in the fetus. The results obtained were similar for the two breeds. The smaller size and better disposition of the Yucatan breed make it preferable for further studies in this field.

Animals↗
PubMed1985

Comparison of [3H]baclofen binding to GABAB receptors in spontaneously hypertensive and normotensive rats.

Baclofen-sensitive GABAB receptor binding to various brain regions was compared in age-matched spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rat. The specific [3H]baclofen binding was significantly higher in SHR cerebellum, hippocampus and nucleus tractus solitarii (NTS), but lower in medulla, when compared with WKY. Scatchard analysis of the binding isotherms indicated a higher Bmax of the high affinity sites in SHR cerebellum and hippocampus and a lower Bmax of the same sites in SHR medulla. Guanyl nucleotide (GTP) decreased [3H]baclofen binding in brain regions of SHR and WKY, although the percentage inhibition of binding did not differ between SHR and WKY. The basal adenylate cyclase activity in SHR cerebellum was lower, in contrast to higher [3H]baclofen binding, whereas lower baclofen binding in SHR medulla was accompanied with higher adenylate cyclase activity. (+/-)Baclofen inhibited adenylate cyclase activity in both SHR and WKY rat brain. Among various regions, the percentage inhibition of cyclase activity in SHR cerebellum was significant lower, as compared to WKY cerebellum. These results suggest that activity of GABABergic mechanisms may be different in SHR and WKY rat brain.

Adenylyl Cyclases↗
PubMed1985

Lignoceroyl-CoA ligase activity in rat brain microsomal fraction: topographical localization and effect of detergents and alpha-cyclodextrin.

Lignoceroyl-CoA ligase activity has been detected in microsomal fractions prepared from rat brain. The synthesis of lignoceroyl-CoA from [1-14C]lignoceric acid and CoASH by this enzyme had an absolute dependence on ATP and Mg2+; ATP could not be replaced by GTP [I. Singh, M. S. Kang, and L. Phillips (1982) Fed. Proc. 41, 1192]. The product has been characterized as lignoceroyl-CoA by the following criteria: Rf on thin-layer chromatography; incorporation of [1-14C]lignoceric acid and [3H]CoASH into the product; acid hydrolysis and identification of the radiolabel in lignoceric acid; and methanolysis and identification of the radiolabel in methyl lignocerate by thin-layer chromatography. The optimal concentrations for CoASH, ATP, and Mg2+ were about 100 microM, 10 mM, and 5 mM, respectively. Lignoceric acid, solubilized by alpha-cyclodextrin, Triton X-100, and deoxycholate, was utilized by the lignoceroyl-CoA ligase, but lignoceric acid solubilized by Triton WR-1339 was not. Topographical localization of lignoceroyl-CoA ligase in the plane of rat brain microsomal membranes was determined by the use of Triton X-100, trypsin, and mercury-Dextran, and was compared with the marker enzymes, ethanol acyltransferase and thiamine pyrophosphatase, which are known to be localized on the luminal (inner) surface of the microsomal vesicles. Mercury-Dextran (100 microM) and trypsin (trypsin:microsomes, 1:56 w/w) treatment of the microsomes inhibited the lignoceroyl-CoA ligase activity by 70 and 90% without disrupting the microsomal vesicles. Disruption of the vesicles with Triton X-100 increased the activity of both ethanol acyltransferase and thiamine pyrophosphatase by 400% but there was no increase in lignoceroyl-CoA ligase activity. These results suggest that lignoceroyl-CoA ligase is localized on the cytoplasmic surface of the microsomal vesicles.

Adenosine Triphosphate↗
PubMed1985

The effect of medroxyprogesterone acetate on the hepatic drug-metabolizing enzymes in normal and protein-deficient female rats.

Effect of depot medroxyprogesterone acetate on the hepatic drug-metabolizing enzymes was studied in female protein-deficient and normal pair-fed rats. Treatment with this drug did not cause any change in organ weight, microsomal protein, and soluble protein yield per gram of tissue in both groups. MPA administration resulted in significant increases in the content of cytochrome P-450 and b5, and activities of benzo[a]pyrene hydroxylase, UDP-glucuronosyltransferase, and NADPH-Cyt c reductase in both pair-fed control and protein-deficient rats. However, the content of glutathione and activity of glutathione-S-transferase were not affected appreciably. The present study suggests that MPA treatment induces drug-metabolizing enzymes in liver to almost the same extent in both protein-deficient and normal pair-fed rats.

Animals↗