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Biomedical subjects

S Khan

Publications and source records attributed to S Khan.

At least 415 records · Page 23Linked to original sources
PubMed1986

Peptides of postulated inhibin activity. Lack of in vitro inhibin activity of a 94-residue peptide isolated from human seminal plasma, and of a synthetic replicate of its C-terminal 28-residue segment.

A 94-residue polypeptide isolated from human seminal plasma and its chemically synthesized C-terminal 28-residue segment were studied in an in vitro inhibin bioassay utilizing rat pituitary cell cultures. Both peptides have previously been claimed to have inhibin activities, and the effects on the secretion and cellular content of gonadotrophins (FSH and LH) were now assessed in the in vitro assay. No inhibition was found. After 72 h of culture, both the cellular content and the spontaneous as well as the LHRH-stimulated release of bioactive or immunoactive FSH and LH remained unaffected. Similarly, no effects were found on the storage and/or release of prolactin, growth hormone, or thyrotropin. We conclude that both the native 94-residue peptide and the synthetic replicate of its C-terminal 28-residue segment, do not influence the pituitary FSH secretion when assessed in this in vitro system.

Animals↗
PubMed1986

Mechanisms of petroleum hydrocarbon toxicity: destruction of liver microsomal and mitochondrial calcium pump activities by a Prudhoe Bay crude oil.

Administration of Prudhoe Bay crude oil (PBCO) to rats resulted in an abrupt drop in liver mitochondrial and microsomal ATP-dependent calcium uptake activity. Also, in vitro incubations of either mitochondria or microsomes in the presence of a dimethyl sulfoxide (DMSO) extract of PBCO resulted in a dose-dependent inhibition of calcium influx. The release of calcium from calcium-loaded mitochondria and microsomes was also observed in the presence of the PBCO extract. At concentrations which effect calcium sequestration, the PBCO extract produced swelling of mitochondria. Microsomal ATPase activity in the presence or absence of calcium was unaffected by PBCO. The results indicate that increased permeability of the membranes to calcium is a contributory factor in the inhibition of calcium uptake by PBCO.

Animals↗
PubMed1986

Immunoreactive calcitonin in amyloid fibrils of medullary carcinoma of the thyroid gland. An immunogold staining technique.

A lymph node containing metastatic medullary carcinoma of the thyroid gland was examined immunohistochemically for the presence of calcitonin by light and electron microscopy. Electron microscopy showed dense, selective labeling of the tumor-associated amyloid fibrils and labeling of the scanty intracytoplasmic neurosecretory granules. By light microscopy, a few tumor cells showed strong staining, whereas the amyloid fibrils showed equivocal staining.

Amyloid↗
PubMed1985

Constraints on flagellar rotation.

The motion of tethered cells of Streptococcus was analyzed at low values of protonmotive force (delta p). Cells repeatedly energized and de-energized stopped at discrete angular positions, indicating a rotational symmetry of barriers to rotation of order 5 or 6. At values of delta p smaller than -30 mV, constraints imposed by these barriers were evident when cells were starved and gradually energized, but not when they were energized first and then gradually de-energized. At values of delta p larger than about -30 mV, the cells behaved as if there were no barriers. Cells spinning in this regime also executed rotational Brownian movement. At energy levels above threshold, the motor determines torque; it does not fix the position of the rotor relative to the stator.

Diffusion↗
PubMed1985

Caffeine tolerance: behavioral, electrophysiological and neurochemical evidence.

The development of tolerance to the stimulatory action of caffeine upon mesencephalic reticular neurons and upon spontaneous locomotor activity was evaluated in rats after two weeks of chronic exposure to low doses of caffeine (5-10 mg/kg/day via their drinking water). These doses are achievable through dietary intake of caffeine-containing beverages in man. Concomitant measurement of [3H]-CHA binding in the mesencephalic reticular formation was also carried out in order to explore the neurochemical basis of the development of tolerance. Caffeine, 2.5 mg/kg i.v., markedly increased the firing rate of reticular neurons in caffeine naive rats but failed to modify the neuronal activity in a group exposed chronically to low doses of caffeine. In addition, in spontaneous locomotor activity studies, our data show a distinct shift to the right of the caffeine dose-response curve in caffeine pretreated rats. These results clearly indicate that tolerance develops to the stimulatory action of caffeine upon the reticular formation at the single neuronal activity level as well as upon spontaneous locomotor activity. Furthermore, in chronically caffeine exposed rats, an increase in the number of binding sites for [3H]-CHA was observed in reticular formation membranes without any change in receptor affinity. We propose, therefore, that up-regulation of adenosine receptors may underlie the development of tolerance to the CNS effects of caffeine.

Action Potentials↗
PubMed1985

Hepatotoxicity in albino rats exposed to n-octane and n-nonane.

Effects of n-octane and n-nonane (1 ml per kg body weight daily) on hepatic and serum enzymes, which reflect abnormal liver function and concentration of lipid and nucleic acid (serum and liver), were studied after 2 and 7 days intraperitoneal administration to albino rats. Decreased activities of serum acetylcholine esterase and carboxyl esterase were observed, together with an increase in FDP aldolase activity. Significant decrease in the concentration of albumin, total protein, and total and esterified cholesterol in serum have been noted after n-octane and n-nonane administration for 7 days. Also, free cholesterol content of liver was elevated significantly after solvents exposure.

Alkanes↗
PubMed1985

The HLA-A, -B, and -DR phenotypes and tuberculosis.

The HLA-A, -B, and -DR antigens were studied in black Americans to analyze deviation in phenotype distribution between ATS Class 3 patients with tuberculosis disease and ATS Class 2 healthy persons with significant tuberculin reaction, but no tuberculosis. Statistical analyses with Fisher's exact test revealed a significant difference in frequency distribution of HLA-B5 (p = 0.046), HLA-DR5 (p = 0.0276), and HLA-DR6y (p = 0.0095) between ATS Class 2 and ATS Class 3 patients. There was a significant decrease in HLA-DR6y (p = 0.01) but increase in HLA-B5 and HLA-DR5 phenotypes in ATS Class 3 patients.

Black People↗
PubMed1984

A study of incidence and relationship of intestinal metaplasia of gastric antrum and gastric metaplasia of duodenum in patients with nonulcer dyspepsia.

The incidence and relationship of intestinal metaplasia of the gastric antrum and gastric metaplasia of the first part of the duodenum were studied in endoscopic biopsies from 120 patients with nonulcer dyspepsia. Intestinal metaplasia was present in 29% of antral biopsies and gastric metaplasia in 39% of duodenal biopsies, with 9% of patients having both. Intestinal metaplasia was not related to alcohol consumption, but was significantly higher in patients who smoked 10 cigarettes or more daily. (P less than 0.002). Gastric metaplasia was associated with duodenitis. Its incidence was significantly higher in males (P less than 0.001) and in patients with a history of high/moderate alcohol intake (P less than 0.02); these findings are reminiscent of the presence of a similar relationship between these factors and duodenal ulcers and support the suggestion that duodenitis and duodenal ulcers probably represent different parts of a single disease spectrum. The presence of both types of metaplasia in 9% of the patients suggest that factors other than gastric acidity may influence the development of metaplasia.

Alcohol Drinking↗
PubMed1983

Isotope and thermal effects in chemiosmotic coupling to the membrane ATPase of Streptococcus.

We measured rates of ATP synthesis by the proton-translocating ATPase of the motile Streptococcus strain V4051. Starved cells were energized artificially by exposing their membranes to a variable electrical potential difference (internal medium negative) and a fixed pH difference (internal medium alkaline). The initial rates of ATP synthesis increased exponentially with protonmotive force. The results were the same in D2O and H2O; there was no solvent isotope effect. At a fixed protonmotive force, the rates were strongly dependent on temperature, as expected for a reaction with a large enthalpy of activation. At a different protonmotive force, the rates varied with temperature in an identical fashion; there was no change in the enthalpy of activation. We conclude that protonation-deprotonation steps are not rate limiting and that the protons that cross the membrane drive ATP synthesis by mass action. The transmembrane electric field acts by changing the concentrations of the reactants, not by changing the configuration of the enzyme-substrate complex.

Adenosine Triphosphatases↗
PubMed1983

Isotope and thermal effects in chemiosmotic coupling to the flagellar motor of Streptococcus.

The torque generated by the flagellar motor of Streptococcus strain V4051 has been determined from rates of rotation of cells tethered by a single flagellum in media of different isotopic composition and temperature. Starved cells were energized artificially with either a potassium diffusion potential or a pH gradient. The torque increased linearly with protonmotive force. Identical results were obtained in media made with D2O or H2O; there was no solvent isotope effect. At a fixed protonmotive force, the torque was approximately constant over a temperature range of 4 degrees -38 degrees C. In cells chemotactically inert to changes in cytoplasmic pH, the motor turned counterclockwise when protons moved inward and clockwise when they moved outward. We conclude that the motor is a reversible engine driven by simple acid-base dissociation. A detailed model is discussed.

Chemotaxis↗
PubMed1983

Assignment of segments of the bacteriorhodopsin sequence to positions in the structural map.

Specific amino acid sequence segments have been assigned to locations in the structural map of bacteriorhodopsin using two-dimensional neutron diffraction data and a model building analysis. Models are constructed computationally by building specific regions of the amino acid sequence as alpha helices and then positioning the helices on axes indicated by the density map of Henderson and Unwin (Nature [Lond.]. 1975, 257:28-32). Neutron diffraction data were collected from samples of stacked, oriented "native" purple membranes as well as purple membranes containing different kinds of deuterated amino acids. Models differing in the assignments of helices to specific axes and in rotations of the helices about those axes were tested against the neutron data using a weighted residual factor to rank the models. This residual factor was calculated between observed and predicted intensity differences for pairs of data sets. Using this approach, a small set of related models has been found that predicts the observed intensity changes between five independent data sets. These models are inconsistent with the proposed locations of the retinal chromophore and the carboxyl terminus and with any of the previously proposed models for bacteriorhodopsin.

Amino Acid Sequence↗
PubMed1982

Effect of n-octane and n-nonane administration on alkaline phosphatase activity in tissues of female rats.

Studies on alkaline phosphatase were conducted in albino rats exposed to n-octane or n-nonane for 2 and 7 days; there was an increase in alkaline phosphatase activity of liver, spleen and bone marrow. Increase in spleen alkaline phosphatase activity persisted up to 42 days after single dose of n-octane or n-nonane. Pretreatment with protein synthesis inhibitors, cycloheximide or ethionine removed this observed increase of alkaline phosphatase activity in liver and spleen.

Alkaline Phosphatase↗