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Biomedical subjects

S Khan

Publications and source records attributed to S Khan.

At least 361 records · Page 20Linked to original sources
PubMed1991

Studies on the effects of some organic pollutants on the heavy metal transport in an Indian soil.

The translocation of some heavy metals, such as Hg, Cd, Cu, Co, Ni and Zn, as affected by organic pollutants, i.e. methanol, ethanol, propanol, formaldehyde, acetaldehyde, benzaldehyde, acetone, ethyl methyl ketone and cyclo-hexanone, was studied in an Indian red soil using soil thin layer chromatography. It was observed that an increase in the concentration of organic compounds in developer enhances the heavy metal mobility, except in the case of Cu and Hg which show a decreasing trend. The results are discussed in relation to the physico-chemical characteristics of the soil and adsorption/desorption phenomena.

Journal Article↗
PubMed1991

A new model of nephrolithiasis involving tubular dysfunction/injury.

To better understand the pathogenesis of nephrolithiasis, we developed a new animal model that closely mimics human calcium oxalate stone disease. Rats were treated with a regimen that combines moderate hyperoxaluria (produced by 10 days of feeding with 3% ammonium oxalate) with mild proximal tubular injury/dysfunction (produced by 8 daily injections of gentamicin sulfate -40 mg./kg.). This combined treatment caused a marked increase in the incidence of calcium oxalate crystals and stones over that seen in animals treated with oxalate or gentamicin alone. Using a semiquantitative scoring system for estimating the abundance of crystals in coronal sections of kidneys, we found that 63% of animals receiving gentamicin plus oxalate showed "moderate" numbers of crystal, as compared to 8% of animals receiving oxalate alone; and the majority of the crystals occurred in the papilla, a pattern similar to that seen in human stone disease. Untreated rats and rats treated with gentamicin alone did not exhibit calcium oxalate crystals or stones. Despite the abundance of crystals and stones, animals receiving gentamicin plus oxalate retained relatively normal renal function as judged by creatinine clearance. Thus, the model has several advantages over preexisting models of nephrolithiasis. Crystal and stone deposition develop rapidly (within 14 days). The pattern of deposition resembles that seen in human stone disease and renal function remains relatively normal. These findings indicate that this model of nephrolithiasis may prove useful for studies of the pathogenesis of stone disease. Moreover, they suggest that renal tubular injury and/or dysfunction may produce conditions conducive to the formation and growth of calcium oxalate stones.

Animals↗
PubMed1991

Increased incidence of hyperbilirubinaemia in 'unchallenged' glucose-6-phosphate dehydrogenase deficiency in term Saudi newborns.

The incidence of severe hyperbilirubinaemia was significantly higher among the G6PD-deficient Saudi infants born at term than in non-deficient babies (34% vs 9%) (p less than 0.005). No apparent offending factors were detected in either the babies or their mothers. All babies who developed hyperbilirubinaemia did so during the 1st week of life. The highest mean bilirubin level for all jaundiced G6PD-deficient babies was recorded on the 4th postnatal day. Although the incidence of severe hyperbilirubinaemia among our neonates was relatively high, only two of them (7%), a boy and a girl, required exchange transfusions. Five of 29 jaundiced babies with G6PD deficiency were readmitted after discharge because of significant jaundice. One required exchange transfusion. Since G6PD deficiency seems to be a relatively common cause of neonatal jaundice in Saudi newborns, early detection of this enzymopathy by cord blood screening is justified to avoid morbidity and deaths.

Female↗
PubMed1991

New structural features of the flagellar base in Salmonella typhimurium revealed by rapid-freeze electron microscopy.

The structure of the flagellar base in Salmonella typhimurium has been studied by rapid-freeze techniques. Freeze-substituted thin sections and freeze-etched replicas of cell envelope preparations have provided complementary information about the flagellar base. The flagellar base has a bell-shaped extension reaching as far as 50 nm into the bacterial cytoplasm. This structure can be recognized in intact bacteria but was studied in detail in cell envelopes, where some flagella lacking parts of the bell were helpful in understanding its substructure. Structural relationships may be inferred between this cytoplasmic component of the flagellum and the recently described flagellar intramembrane particle rings as well as the structures associated with the basal body in isolated, chemically fixed flagella.

Flagella↗
PubMed1991

Synaptosomal respiration: a potent indicator of veratridine-induced Na influx.

Inhibition of the voltage-dependent Na channel by tetrodotoxin (5 mumol/l) decreased by about 86% the stimulation of the respiration of rat brain synaptosomes induced by veratridine (10 mumol/l). A similar effect was achieved by blocking Na(+)-K(+)-ATPase with ouabain (1 mmol/l). Pharmacological manipulations of Ca homeostasis suggested that the veratridine-induced stimulation of respiration did not depend upon Ca entry. These data suggest that the veratridine-induced stimulation of synaptosomal respiration may result primarily from an increase in intracellular Na+. They provide the basis for an indirect method, which only requires recording of synaptosomal respiration, to test drugs for their possible interaction with excessive Na influxes.

Amiloride↗
PubMed1991

Effect of chemotherapy on circulating steroid hormone levels in postoperative premenopausal breast cancer patients.

Serum levels of 17-beta oestradiol, testosterone and progesterone were determined in postoperative premenopausal breast cancer patients. In patients receiving chemotherapy circulating 17-beta oestradiol values decreased significantly compared to control group during the sampling/drug regimens employed. Among the control group, however, the oestradiol levels remained high throughout the sampling period. Testosterone levels in patients were also significantly low compared to control group throughout the sampling regimen up to 28 days. In contrast the levels of progesterone in patients were elevated and remained high compared to the corresponding controls. A positive correlation was found between the drop in serum oestradiol and testosterone levels following the initiation of chemotherapy and the regression of the tumour size. Steroid hormone levels in the serum of breast cancer patients receiving chemotherapy can serve as clinical tools to monitor the progress of the disease and response to therapy.

Adult↗
PubMed1991

Zinc protection against lipid peroxidation from cadmium.

Effect of zinc and cadmium on lipid peroxidation and catalase activity in liver, heart, brain and testis was determined in order to characterise the interaction of zinc with cadmium. Zinc and cadmium both increased lipid peroxidation significantly in the tissues studied. In animals pretreated with zinc prior to cadmium administration, significant decrease in lipid peroxidation in liver was observed. Lipid peroxidation was not affected significantly in testis but a significant increase was observed in heart and brain tissues. Catalase activity in testis increased significantly by zinc treatment with or without cadmium administration.

Animals↗
PubMed1991

Cell cycle kinetic studies in human cancers. Development of three DNA-specific labels in three decades.

Controversy has epitomized the prognostic and clinical significance accorded to cell cycle kinetic studies in neoplastic diseases. Recent introduction of monoclonal antibodies to thymidine analogues such as iododeoxyuridine and bromodeoxyuridine has unveiled a spectacular new area of research. Large numbers of patients with liquid and solid tumors have been interrogated by introducing iododeoxyuridine and bromodeoxyuridine as DNA-specific probes in vivo. Further in vitro incubation of S-phase cells already double-labeled in vivo with tritiated thymidine has added a whole new dimension to the kinds of questions that can now be addressed with alacrity. Time is rapidly approaching when this information will be available in a prompt enough fashion to be useful for planning therapeutic strategies. Reviewed are the salient features of the rapid progress achieved in the last decade in this exciting discipline.

Acute Disease↗
PubMed1990

Risk factors for coronary heart disease in the Indians of Durban.

Coronary heart disease (CHD) is a major problem in migrant Indians throughout the world. In South Africa it has reached 'epidemic' proportions. A field survey was conducted among Indians in the metropolitan area of Durban to determine the prevalence and known risk factors for CHD. In a study of 778 subjects aged 15-69 years (408 men), 15.3% (sex and age adjusted 13.4%) had a history of CHD. The important risk factors in men were hypercholesterolaemia, hypertriglyceridaemia, diabetes, and smoking, and in women diabetes, hypercholesterolaemia, and hypertriglyceridaemia. The minor risk factors were hyperuricaemia, sedentary occupation, obesity in women and a positive family history of CHD. A study of the major risk factors leading to CHD showed that 52% (sex and age adjusted 45.5%) had at least one major risk factor at the higher (level A) and 68% (sex and age adjusted 61.9%) at the lower (level B) risk levels. Diabetes mellitus was strongly associated with a positive history of CHD. In 47.6% (sex and age adjusted 48.2%) of the total group resting ECG abnormalities were found that could be coded. Because of the severe nature of CHD in the migrant Indian, an immediate and intensive programme of primary prevention of CHD risk factors should be instituted.

Adolescent↗
PubMed1990

Accumulation of low molecular weight (bleomycin detectable) iron in bone marrow cells of rats after benzene exposure.

An accumulation of low molecular weight (LMW) bleomycin detectable iron in the bone marrow was observed after administration of benzene (IP 0.5 ml/kg, daily) for 5 and 10 days in female albino rats. However, this LMW iron was not detectable in the bone marrow of rats from the control group. Studies of bone marrow fractionation showed that the maximum accumulation of this LMW iron was in the mitochondrial fraction. An increase in the activity of superoxide dismutase and lipid peroxidation was also noticed in the benzene exposed groups.

Animals↗
PubMed1990

Fascinating rhythm: a primer on chaos theory and its application to cardiology.

Nonlinear dynamics is an exciting new way of looking at peculiarities that in the past have been ignored or explained away. We have attempted to give a general introduction to the basics of the mathematics, applications to cardiology, and a brief review of the new tools needed to use the concepts of nonlinear mathematics. The careful mathematical approach to problems in cardiac electrical dynamics and blood flow is opening a window on behaviors and mechanisms previously inaccessible.

Animals↗
PubMed1990

Energy transduction in the bacterial flagellar motor. Effects of load and pH.

The effect of load and pH on the relation between proton potential and flagellar rotation has been studied in cells of a smooth-swimming Streptococcus strain. The driving potential, speeds of free-swimming bacteria, and rotation rates of bacteria tethered to glass by a single flagellum were measured. The relation between rotation rate of tethered bacteria and potential was remarkably linear up to nearly -200 mV. The relation between swimming speed and potential exhibited both saturation and threshold, as previously observed in other species. The form of these relations depended on pH. The equivalence of the electrical and chemical potential components of the proton potential in enabling swimming depended on the voltage. Our observations may be most simply accommodated by a kinetic scheme that links transmembrane proton transits to a tightly coupled work cycle. The properties of this scheme were elucidated by computer simulations of the experimental plots. These simulations indicated that the protonable groups that participate in the rate limiting reactions have a fractional electrical distance between three-fourths to all of the way toward the cytoplasm with a corresponding mean proton binding affinity of 10(-7.3)-10(-7.0) M, respectively.

Cell Membrane↗
PubMed1990

Delayed start-up of kinesin-driven microtubule gliding following inhibition by adenosine 5'-[beta,gamma-imido]triphosphate.

Kinesin is a microtubule-activated ATPase that moves objects toward the plus end of microtubules and makes microtubules glide along a glass surface. Here we investigate a remarkable effect of the nonhydrolyzable analogue of ATP, adenosine 5'-[beta,gamma-imido]triphosphate (p[NH]ppA), on kinesin-driven microtubule gliding. Microtubule gliding that has been blocked by rapid replacement of ATP with p[NH]ppA requires 1-2 min of exposure to ATP before microtubule gliding resumes. This latency is not shortened by prolonged washing of p[NH]ppA-blocked microtubules in nucleotide-free buffer for up to 15 min, suggesting that ATP binding to a second nucleotide binding site on kinesin triggers the release of bound p[NH]ppA. To test this hypothesis, the release of [3H]p[NH]ppA from kinesin-microtubule complexes was followed in parallel biochemical assays. In nucleotide-free buffer, the bound p[NH]ppA was released over several hours from the complexes. However, addition of ATP caused the release of p[NH]ppA from the kinesin-microtubule complexes within 2 min, which was similar to the latent period for start-up of microtubule gliding after p[NH]ppA inhibition. The stoichiometry of p[NH]ppA bound per kinesin heavy chain at saturation was estimated to be approximately 1:2. These results suggest a model in which each molecule of kinesin has at least two nucleotide binding sites that alternately bind nucleotide.

Adenosine Triphosphatases↗
PubMed1990

Paradoxical effects of maternal stress on fetal steroids and postnatal reproductive traits in female mice from different intrauterine positions.

We examined effects of maternal stress on prenatal serum concentrations of testosterone and estradiol and on postnatal reproductive traits in female mice from different intrauterine positions. On Day 18 of fetal life, control females positioned in utero between two male fetuses (2M females) had higher concentrations of testosterone and lower concentrations of estradiol in serum than control female fetuses located between two females (0M females). Control females positioned between a male and a female fetus (1M females) had intermediate levels of both hormones. Prior intrauterine position in control females accounted for differences in genital morphology (length of the anogenital separation) at birth and length of estrous cycles during adulthood. Maternal stress eliminated these postnatal differences due to prior intrauterine position: all 0M, 1M, and 2M female offspring of stressed mothers exhibited postnatal traits that were indistinguishable from those of control 2M females. Maternal stress resulted in an increase of over 1 ng/ml in serum testosterone in all female fetuses; the magnitude of the increase was similar for 0M, 1M, and 2M females. There was no effect of maternal stress on serum concentrations of estradiol in 0M and 2M female fetuses. Maternal stress resulted in a dramatic change in the postnatal traits of 0M females, whereas 2M females showed no change. Since the effect of maternal stress on sex steroids was similar among fetuses from different intrauterine positions but postnatal response to maternal stress varied by intrauterine position, other components of the endocrine system may mediate effects of maternal stress on these postnatal characteristics.

Animals↗
PubMed1990

Molecular cloning and sequencing of an Australian isolate of proviral bovine leukaemia virus DNA: comparison with other isolates.

The molecular cloning and characterization of an EcoRI fragment, 8.26 kb in size, of an Australian isolate of bovine leukaemia virus (pBLV-A1) is described. This fragment includes most of the proviral genome as well as 340 bp of flanking bovine DNA sequence at the 5' end. Approximately 790 bp, including the 3' long terminal repeat, was missing from this clone. At the level of restriction enzyme mapping, this isolate could be distinguished from American, Belgian and Japanese isolates. DNA sequencing of the entire clone demonstrated some variation at the amino acid level between pBLV-A1 and the Japanese and Belgian isolates, particularly in the gag gene. In that gene there were 59 amino acid changes compared to the Japanese isolate and 24 compared to the Belgian isolate. The greater number in the case of the Japanese isolate was due to both single nucleotide changes and frameshift in a single region of the gene. This study also demonstrates that there are large tracts of amino acid sequence, particularly within the env and pol genes, that are highly conserved in different isolates. Some of these conserved sequences exist in regions containing epitopes important in virus infectivity.

Amino Acid Sequence↗