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Biomedical subjects

G Singh

Publications and source records attributed to G Singh.

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

Evidence for lack of mitochondrial DNA repair following cis-dichlorodiammineplatinum treatment.

The purpose of this study was to determine whether cis-dichlorodiammineplatinum (cisplatin) causes mitochondrial DNA (mtDNA) damage. A specific and sensitive method for quantitation of damage to mtDNA was used, by which the physical forms of mtDNA (supercoiled, open circular and linear forms) were separated by gel electrophoresis. The DNA specificity was then obtained by hybridizing with a mtDNA probe. In vitro incubation of mtDNA with cisplatin showed that the drug did not induce any changes in the proportion of physical forms; similar results were obtained in vivo. Since cisplatin did not cause any strand scission in mtDNA but induces strand breaks in nuclear DNA, which is an indirect effect, a lack of repair for cisplatin-induced adducts in mtDNA is suggested.

Animals↗
PubMed1990

Atrial natriuretic factor activates membrane-bound guanylate cyclase of chief cells.

The present study examined the effect of atrial natriuretic factor (ANF) on cGMP generation by dispersed chief cells from guinea pig stomach. ANF caused a rapid dose-dependent increase in cGMP, a 7-fold increase in cGMP caused by 1 microM ANF, with or without 3-isobutyl-1-methylxanthine present. Methylene blue reduced cGMP in response to nitroprusside but not ANF. Guanylate cyclase activity of a chief cell membrane fraction doubled in response to ANF, but was not affected by nitroprusside. ANF had no effect on guanylate cyclase activity of the soluble fraction of lysed chief cells. Dose-response curves for whole cell cGMP production and membrane guanylate cyclase activity in response to ANF were closely related. These data indicate that ANF increases chief cell cGMP production by activating particulate guanylate cyclase, providing functional evidence that chief cells possess surface membrane receptors for ANF.

Animals↗
PubMed1990

Dissipation of s-triazines and thiocarbamates from soil as related to soil moisture content.

Half-lives (t1/2) of two soil incorporated s-triazines (atrazine and prometon) and two thiocarbamate (EPTC and triallate) herbicides were determined in relation to soil moisture content in two California soils. Treated soils were incubated at three moisture levels in aerated glass vials at 25 +/- 1 degree C and were analyzed at 0, 7, 16, 28, 56 and 112 day intervals. Loss of herbicides in all treatments followed first-order kinetics. The t1/2-values of all herbicides decreased with increasing soil moisture and followed an empirical equation, t1/2 = aM(-b) (where t1/2 is half-life; M the moisture content; and a and b are constants). Soil moisture had a greater effect on carbamates than on s-triazines . Prometon exhibited the longest half-life in both soils, whereas EPTC was least persistent in one soil and atrazine in another. The t1/2-values for atrazine, prometon, EPTC, and triallate with medium moisture levels and 10 microg/g concentration were 34.6, 43.2, 25.4 and 38.1 days in sandy loam and 26.5, 44.4, 44.1 and 25.9 days in loamy sand, respectively. Disappearance of 50% of the applied concentrations of most of the herbicide-soil combinations (except EPTC and triallate in one soil) took longer for lower initial concentrations (1 microg/g) than for higher concentrations (10 microg/g).

Journal Article↗
PubMed1990

Hydrocephalus induced by cyclophosphamide in chick embryos.

Cyclophosphamide was injected into the yolk sac of chick embryos for 6 days (Days 0-5). Embryos collected on the 21st day of incubation had a 37% incidence of hydrocephalus. Agenesis or stenosis of the aqueduct, as well as hypertrophy of the choroid plexus, was observed in 20% of the embryos.

Animals↗
PubMed1990

Factors affecting production and activity of phospholipase C by Yersinia enterocolitica.

The production of phospholipase C by Yersinia enterocolitica strain SG was optimum at 37 degrees C at pH 6.5. No enzyme activity could be detected when the organism was grown at extreme pH values (pH greater than 8.5 or less than 5.0). The enzyme production was maximum when the organism was grown under static conditions in TSB medium. All solvents and salts inhibited the enzyme activity, whereas loss of activity was 95% in presence of methanol (20%) and 99% in presence of sodium azide (0.2 mol/l). The enzyme activity was increased twofold in the presence of cysteine and decreased by 98% in the presence of sodium perchlorate (0.2 mol/l).

Culture Media↗
PubMed1990

Spontaneous lymphocyte proliferation in severe periodontal disease: role of T and B cells.

Spontaneous proliferation of T cells, B cells and unseparated lymphocytes was studied in patients with severe periodontal disease and control subjects. In the patient group only, spontaneous lymphocyte proliferation was reduced, whereas B cell proliferation was enhanced. The findings offer further support for the existence of a disturbance in immune regulation in patients with severe periodontal disease.

Adult↗
PubMed1990

Preheparinization improves organ function after hemorrhage and resuscitation.

Recent studies indicate that heparinization before hemorrhage maintains microvascular patency in the liver and kidney during and after severe hemorrhagic shock. However, it is not known whether preheparinization has any protective effects on organ function after hemorrhage and resuscitation. To study this, unanesthetized rats (with or without preheparinization) were bled to and maintained at a mean arterial pressure of 40 mmHg until 40% of the maximum shed blood volume was returned in the form of Ringer lactate (RL). They were then resuscitated with four times the volume of the shed blood with RL. Cardiac output (CO), [3H]inulin clearance (CIn; renal function), hepatic microvascular blood flow (HMBF), and hepatocellular function (HF), i.e., maximal velocity of indocyanine green clearance (Vmax), were determined 1.5 h after resuscitation. Although CO decreased in both groups, the values in preheparinized rats were significantly higher than in the nonheparinized rats. The improvement in CIn as well as HMBF followed the same trends. HF (Vmax) was significantly depressed in the nonheparinized rats but was maintained in preheparinized rats. Thus administration of heparin before the onset of hemorrhage improves CO and renal function and restores HF to control after hemorrhage and resuscitation. These protective effects of preheparinization could be due to the maintenance of microvascular patency and prevention of blood sludging during and after hemorrhage.

Animals↗
PubMed1990

Induction of surfactant protein (SP-A) biosynthesis and SP-A mRNA in activated type II cells during acute silicosis in rats.

The synthesis of the major surfactant protein, SP-A, was studied in activated alveolar type II cells isolated from the lungs of rats exposed to silica by intratracheal instillation. Exposure of rats to silica resulted in large increases in the levels of disaturated phosphatidylcholine and SP-A in the extracellular and intracellular surfactant compartments. Isolated type II cells were used to determine if the observed increases in SP-A were associated with increased SP-A synthesis. Type II cells were isolated by a combination of elastase digestion, centrifugal elutriation, and differential adherence on IgG-coated petri dishes. Type II cells from silica-treated lungs were separated into two populations, designated type IIA and type IIB. The type IIB, or activated population, consisted of type II cells that were larger than normal type II cells and, in addition, contained larger and more numerous lamellar bodies than normal type II cells. Type IIB cells contained 4.3-fold higher levels of SP-A compared to normal type II cells. SP-A synthesis was measured by incubating freshly isolated cells with [35S]Translabel (70% [35S]methionine, 15% [35S]cysteine) for up to 4 h in methionine-free medium, followed by immunoprecipitation of newly synthesized protein. The rate of SP-A synthesis was increased approximately 6.7-fold in the activated type II cells. Analysis of the newly synthesized protein by one-dimensional SDS-PAGE indicated three intracellular forms of SP-A with molecular weights of approximately 26,000, 30,000, and 34,000. In type II cells from control rats, the 34-kD protein accounted for approximately 93% of the newly synthesized SP-A after 4 h of incubation; only a small amount of radioactivity was associated with the lower molecular weight species. The increased biosynthesis of SP-A in the activated type II cells was associated with a 7.3-fold increase in the level of SP-A mRNA. These results indicate that the content and synthesis of SP-A are both highly elevated in activated type II cells and that these increases may be due to increased levels of SP-A mRNA.

Animals↗
PubMed1990

Antibody to collagen type I in gingival crevicular fluid.

Gingival crevice fluid (GCF) was collected from inflamed sites in 20 patients before and 6 weeks after treatment. Levels of IgG to human collagen Type I were measured in the GCF and autologous serum using an enzyme-linked immunosorbent assay and compared with levels in control sera. IgG antibody to collagen was detected in GCF at significantly (P less than 0.01) higher levels than in control sera, but these levels were not significantly (P greater than 0.05) different from those in autologous sera. The levels of IgG antibody in GCF and autologous sera did not alter significantly (P greater than 0.05) after treatment. IgG antibody to collagen Type I is present in GCF in the diseased and healing state.

Adult↗
PubMed1990

Long-term follow-up study of mitomycin eye drops as adjunctive treatment of pterygia and its comparison with conjunctival autograft transplantation.

We observed 48 patients for 7-21 months (mean, 18 months) after pterygium excision and 2 weeks of placebo or mitomycin topical therapy to evaluate whether or not the short-term efficacy of mitomycin in preventing pterygium recurrence would be reflected in long-lasting efficacy as well. Placebo-treated pterygia showed a 73% recurrence rate. One of 58 (1.7%) mitomycin-treated pterygia recurred (p less than 0.05). We also performed a pilot study comparing pterygia treated with excision followed by 0.4 mg/ml of mitomycin to pterygia treated with excision coupled with conjunctival autograft transplantation to estimate the number of patients required for a randomized clinical trial comparing these two treatment modalities and thereby to decide whether or not such a study would be justified. Thirteen primary and two recurrent pterygia were treated with mitomycin, while 14 primary and one recurrent pterygia were treated with conjunctival autograft transplantation. With mean follow-up times of 4 and 6 months, respectively, no recurrences were noted in the mitomycin-treated group, while the conjunctival autograft transplantation group had one recurrence (6.6%). We estimate that 400 patients would be required for a properly designed clinical trial comparing these two effective therapies for prevention of recurrent pterygia. We conclude that such a study is unjustified, and further conclude that the vastly less expensive, simple therapy of mitomycin eye drops is the more appropriate treatment.

Administration, Topical↗
PubMed1990

Ultrastructure of the monkey vas deferens.

The testicular and prostatic ends of the vasa deferentia of two male monkeys weighing 3-4 kg were examined ultrastructurally, using the method described by Richards & Tranzer (1975). The general ultrastructure of the vas deferens resembles that described previously. In addition, new features were observed. These include (i) shedding of parts of the apical portions of the epithelial cells; (ii) darkening of mitochondria-rich cells in the epithelium; (iii) presence of secretory granule-like structures in the principal cells of the epithelium; (iv) mast cells which may be associated with blood vessels or smooth muscle cells, and (v) presence of dense osmiophilic cells in the lamina propria and muscle coat, but predominantly in the former. The last-mentioned cells are stellate, having many branching processes, and are characterised by the appearance of many caveolae on their surface membranes. Basal lamina may or may not be seen to surround the cell membranes. The cells are contacted by nerve varicosities which resemble those of cholinergic and purinergic fibres.

Animals↗