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Biomedical subjects

M S Khan

Publications and source records attributed to M S Khan.

At least 37 records · Page 2Linked to original sources
PubMed2001

Spin-dependent exciton formation in pi-conjugated compounds.

The efficiency of light-emitting diodes (LEDs) made from organic semiconductors is determined by the fraction of injected electrons and holes that recombine to form emissive spin-singlet states rather than non-emissive spin-triplet states. If the process by which these states form is spin-independent, the maximum efficiency of organic LEDs will be limited to 25 per cent. But recent reports have indicated fractions of emissive singlet states ranging from 22 to 63 per cent, and the reason for this variation remains unclear. Here we determine the absolute fraction of singlet states generated in a platinum-containing conjugated polymer and its corresponding monomer. The spin-orbit coupling introduced by the platinum atom allows triplet-state emission, so optically and electrically generated luminescence from both singlet and triplet states can be compared directly. We find an average singlet generation fraction of 22 +/- 1 per cent for the monomer, but 57 +/- 4 per cent for the polymer. This suggests that recombination is spin-independent for the monomer, but that a spin-dependent process, favouring singlet formation, is effective in the polymer. We suggest that this process is a consequence of the exchange interaction, which will operate on overlapping electron and hole wavefunctions on the same polymer chain at their capture radius.

Journal Article↗
PubMed2001

The energy gap law for triplet states in Pt-containing conjugated polymers and monomers.

The energy gap law established for aromatic hydrocarbons and rare earth ions relates the nonradiative decay rate to the energy gap of a transition through a multiphonon emission process. We show that this energy gap law can be applied to the phosphoresce of a series of conjugated polymers and monomers for which the radiative decay rate has been enhanced through incorporation of a heavy metal. We find that the nonradiative decay rate from the triplet state T(1) increases exponentially with decreasing T(1)-S(0) gap for the polymers and monomers at 300 and 20 K. Comparison of the nonradiative decay of polymers with that of their corresponding monomers highlights the role of electron-lattice coupling.

Journal Article↗
PubMed2001

Changes in R-R and Q-T intervals following cardiac vagotomy in neonatal swine.

Asymmetric innervation of the myocardium, especially a predominance of sympathetic innervation, may establish conditions whereby electrical instability could result. Using a swine animal model, we studied the effect of right cardiac vagal denervation on the variability of R-R and Q-T intervals. Newborn pigs were assigned randomly to two groups: sham-operated controls (C), or denervation of the right cardiac vagus nerve (RCVX). EKGs were recorded weekly until the two groups exhibited significant heart rate differences. Analysis of the EKG included measurements of R-R and Q-T intervals and corrected Q-T intervals (QTc). Poincaré plots were used to display age-related differences in R-R and Q-T intervals. For RCVX animals, decreased QTc and R-R intervals were noted at 6 and 7 weeks after denervation, respectively. Unexpectedly, one RCVX animal exhibited marked sudden pauses in sinus rhythm. These data indicated that reduced vagal cardiac modulation during development might alter cardiac electrical stability in conscious swine.

Age Factors↗
PubMed2000

Estradiol causes a dose-dependent stimulation of prostate growth in castrated beagle dogs.

BACKGROUND: Previous studies have shown that chronic treatment of castrate dogs with androgen and estrogen results in significant prostate growth. Estrogen treatment of castrate dogs in the absence of androgen has resulted in conflicting data as reported by several authors. The purpose of this experiment was to evaluate the effect of a physiological dose of estradiol on prostate growth in dogs, using ultrasound to study size changes over time. METHODS: Dogs (n = 25) were randomly divided into groups (n = 5) and treated as follows: castration alone (CC), castration plus low dose estradiol (E(2) low), castration plus high estradiol (E(2) high), castration plus estradiol and androstanediol (E(2)A), or no treatment (normal controls, NC). Silastic implants containing 5alpha-androstan-3alpha-17beta-diol (3alphadiol), and/or 17beta-estradiol were used for continous delivery of steroids. Prostate volume was measured by transrectal ultrasonography, and blood was drawn for hormone and sex hormone binding globulin (SHBG) determinations. RESULTS: Results show that serum estradiol and SHBG levels were fairly constant over 12 weeks in all groups. Estradiol-treated groups had mean serum estradiol values of approximately 40 and 60 pg/ml, respectively. Initially, all groups had similar prostate volumes. Over 12 weeks the castrate dogs had a decline in prostate volume, whereas the intact dogs and those treated with E(2) and 3alpha-diol maintained a constant prostate volume. Estradiol treatment caused a large, late onset (week 7), dose-dependent increase in prostate volume relative to the intact group (P < 0.01). At 12 weeks, animals were euthanized and prostates weighed. The mean prostate weights in each group were: NC 14.8 +/- 2. 9, CC 2.4 +/- 0.5, E(2)A 9.7 +/- 2.0, E(2) low 21.7 +/- 4.3, and E(2) high 63.6 +/- 12.6 g (geometric mean +/- SEM). Histologically, prostates of estrogen-treated dogs showed metaplastic squamous epithelium. CONCLUSIONS: These results demonstrate that estradiol causes marked dose-dependent stimulation of prostate growth in the castrate dog.

Anabolic Agents↗
PubMed2000

Fine-needle aspiration diagnosis of Kaposi's sarcoma in a developing country.

Fine-needle aspiration (FNA) cytology was performed on 15 patients with peripheral lymphadenopathy and/or skin lesions referred to the Department of Pathology of the Hospital Central of Maputo, Maputo, Mozambique. Epitrochlear lymph nodes were the most frequently aspirated site. All aspirates allowed diagnoses of Kaposi's sarcoma (KS). Smears contained loosely cohesive clusters of bland spindle cells, with a radial arrangement and nuclear crush artifacts. These diagnostic clues have not been described in other spindle-cell intranodal lesions that should be considered in differential diagnoses. Taking into consideration the high prevalence of AIDS and limited resources for diagnosis in Africa, FNA cytology appears to be a useful method for the diagnosis of KS in developing countries, reducing the necessity for surgical lymph node excision.

AIDS-Related Opportunistic Infections↗
PubMed2000

Development of a blocking enzyme-linked immunosorbent assay for the detection of avian polyomavirus-specific antibodies.

Avian polyomavirus, described originally as budgerigar fledgling disease virus, has been associated with devastating contagious disease outbreaks in budgerigar aviaries. At present, this virus affects a wide range of psittacine and non-psittacine birds worldwide, and the serum neutralisation test is used for the serodiagnosis of avian polyomavirus infections. A blocking enzyme-linked immunosorbent assay was developed for the screening of large numbers of sera collected from various avian species. The assay employs a monoclonal antibody directed against the major structural protein VP1 as a blocking antibody in a sandwich blocking procedure. Either purified avian polyomavirus particles or avian polyomavirus VP1 expressed in recombinant baculovirus-infected Sf9 cells were used as antigen. The specificity of the blocking enzyme-linked immunosorbent assay was evaluated by testing sera directed against mammalian polyomaviruses. Using sera obtained from chicken infected experimentally with avian polyomavirus and a collection of psittacine field-origin sera, a good correlation was observed between the results of the blocking enzyme-linked immunosorbent assay and the serum neutralisation test. However, the blocking enzyme-linked immunosorbent assay is more rapid and more economic. Both, avian polyomavirus particles and VP1 produced by recombinant DNA technology proved to be suitable antigens.

Animals↗
PubMed2000

Electronic spectra of 1-methyl and 2-methyl phenanthrenes and their radical cations.

Electronic spectra of phenanthrene (P), 1-methyl phenanthrene (1-MeP), 2-methyl phenanthrene (2-MeP) and their monopositive ions are investigated experimentally as well as theoretically. The ions were produced by photo-oxidation of the hydrocarbons in boric acid matrix. The electronic absorption spectrum of 2-methyl phenanthrene cation (2-MeP+) is entirely new. For the interpretation of the electronic spectra of neutral and ionized MePs, semi-empirical AM1 (Austin Model 1) calculations are carried out for the first time. The bathochromic shifts in the spectral bands of the neutral and ionized MePs are attributed to 'conjugative' effect. The present experiments reveal that the 448 nm band of 1-methyl phenanthrene cation (1-MeP+) and the 486 nm band of 2-MeP+ show close matching with the respective 450 nm and 488 nm 'diffuse interstellar bands'. This suggests the possibility of the existence of such ionic species in the interstellar matter.

Cations↗
PubMed2000

Renal transplantation in patients with an augmentation cystoplasty.

OBJECTIVE: To retrospectively review our experience over a 10-year period of renal transplantation in patients with augmented bladders and thus assess the safety of this procedure. PATIENTS AND METHODS: Ten transplant recipients who had previously undergone augmentation cystoplasty were reviewed; a cadaveric kidney was transplant in each case. The donor ureter was anastomosed to the augment bladder in six patients, in three to the native ureter and in one the donor renal pelvis was anastomosed to the native ureter. RESULTS: No patients died and nine of the 10 grafts were functioning at a mean follow-up of 27 months. The mean (SD) serum creatinine level at the follow-up was 100.8 (27.25) mmol/L. Four patients had 10 episodes of urosepsis requiring hospital admission, with only one graft lost. CONCLUSION: Renal transplantation can be performed safely in patients with an augmentation cystoplasty.

Adolescent↗
PubMed2000

An immunohistochemical study of the rete ovarii and epoophoron.

A study to compare the immuno-histochemical profile of the human rete ovarii, and epoophoron, with the Fallopian tube and ovarian surface epithelium was performed with 31 antibodies and antisera. A reaction was present in the epithelial cytoplasm of the rete ovarii and epoophoron of mesonephric origin, for vimentin, GFAP, cytokeratin markers, (AE1/AE3, MNF116; Cam 5.2, 34 beta E12 and for the monospecific antibodies to cytokeratins 7 and 19), heat shock protein 27, in the cell membrane for HBME-1, EMA and in the subepithelial collagen for collagen IV. Reactions were present only in the epithelium in the rete ovarii for EGFR (one case) and CA-125 (four cases). A reaction was present in the epithelium of the epoophoron only for Ber-EP-4 and S100. There was no reaction with antibodies for desmin, neurofilament protein, cytokeratins 20 or 14, actin, calretinin, E-cadherin, C-erb-B2, or CEA (monoclonal and polyclonal reagents). The immuno-histochemical profile of the Fallopian tube was consistent with its para-mesonephric origin and that in the ovarian surface epithelium was consistent with a proposed modified mesothelial origin. This study provides an immunohistochemical profile of these structures with a large panel of commonly available antibodies and antisera, confirming and extending the findings described in previous studies.

Antigens, Surface↗
PubMed2000

The ycf 9 (orf 62) gene in the plant chloroplast genome encodes a hydrophobic protein of stromal thylakoid membranes.

There are still some open reading frames, orfs, with unknown function in the higher plant chloroplast genome. Of these conserved orfs, designated as ycfs (hypothetical chloroplast open reading frames), one is ycf 9 (orf 62) in the transcription unit with the psbC and psbD genes. The aim of this work was to investigate the function of ycf 9 by insertional inactivation of the gene with a selectable marker cassette, consisting of the aadA coding region connected to the trc promoter and rrnB terminator. This cassette was inserted 19 bp downstream from the start of the coding region of the tobacco ycf 9 gene. Two DNA constructs with the aadA cassette in opposite orientations were precipitated on 1 micron gold particles and delivered into leaves of Nicotiana tabacum, cultivar Samsun, by the biolistic method. Spectinomycin-resistant plants regenerated following bombardment with only the construct containing the aadA gene in the opposite orientation as ycf 9. In spite of several subsequent regeneration cycles on spectinomycin, the transplastomic plants did not reach homoplasmicity. This suggests that the ycf 9 gene product is essential for chloroplast function. Using a polyclonal antibody raised against the inner part of the gene product, the polypeptide was localized in the stromal thylakoid membranes of chloroplasts.

Amino Acid Sequence↗
PubMed1999

Endothelium modulated vasorelaxant response of a polypharmaceutical herbal drug (lipotab) and its individual constituents.

The present study was undertaken to examine the endothelium modulated effects of polypharmaceutical drug lipotab and its individual ingredients in isolated aortic rings of rat. Endothelium intact and denuded aortic rings were precontracted with phenylephrine 10(-6) M and drugs were added in cumulative manner in concentration ranging from 1 to 50 microg/ml. The results demonstrated an endothelium-dependent vasorelaxant effect of lipotab and its individual ingredients, with the exception of nicotinic acid. The dose dependent relaxant response of nicotinic acid was not altered significantly in the endothelium-denuded rings, suggesting a direct effect of the drug on the vascular smooth muscle. Vasorelaxant effect of lipotab and its individual constituents suggests the therapeutic potential of these compounds in certain cardiovascular diseases.

Animals↗
PubMed1999

Fluorescent antibiotic resistance marker for tracking plastid transformation in higher plants.

Plastid transformation in higher plants is accomplished through a gradual process, during which all the 300-10,000 plastid genome copies are uniformly altered. Antibiotic resistance genes incorporated in the plastid genome facilitate maintenance of transplastomes during this process. Given the high number of plastid genome copies in a cell, transformation unavoidably yields chimeric tissues, which requires the identification of transplastomic cells in order to regenerate plants. In the chimeric tissue, however, antibiotic resistance is not cell autonomous: transplastomic and wild-type sectors both have a resistant phenotype because of phenotypic masking by the transgenic cells. We report a system of marker genes for plastid transformation, termed FLARE-S, which is obtained by translationally fusing aminoglycoside 3"-adenyltransferase with the Aequorea victoria green fluorescent protein. 3"-adenyltransferase (FLARE-S) confers resistance to both spectinomycin and streptomycin. The utility of FLARE-S is shown by tracking segregation of individual transformed and wild-type plastids in tobacco and rice plants after bombardment with FLARE-S vector DNA and selection for spectinomycin and streptomycin resistance, respectively. This method facilitates the extension of plastid transformation to nongreen plastids in embryogenic cells of cereal crops.

Chloroplasts↗
PubMed1999

The expression of the proliferation marker Ki-67 and oestrogen and progesterone receptors in the proximal and distal fallopian tube.

Significant epithelial proliferation is identified more frequently in the fallopian tube in patients with ovarian tumours than in control patients. More extensive sampling of the fallopian tube is also associated with a more frequent identification of epithelial proliferation. We compared cellular proliferation at either end of the fallopian tube as detected with an antiserum to the Ki-67 protein. Variations in oestrogen and progesterone receptor proteins were also examined. Proliferative activity as expressed by the Ki-67 protein, and oestrogen receptor expression was greater in the proximal fallopian tube and progesterone receptor expression was greater in the distal fallopian tube. Only the difference in progesterone receptor expression was statistically significant (P =0.0431). This study indicates that variations in Ki-67, oestrogen and progesterone receptor protein expression occur at different sites in the fallopian tube. This should be taken into account when planning studies of epithelial cell proliferation in the fallopian tube in the future.

Journal Article↗
PubMed1999

Ki-67, oestrogen receptor, and progesterone receptor proteins in the human rete ovarii and in endometriosis.

AIM: To examine proliferative activity using the Ki-67 protein, oestrogen receptor protein, and progesterone receptor protein expression in the rete ovarii, and to make comparisons with their expression in endometriosis. METHODS: Immunohistochemistry was used to study the rete ovarii in 24 cases and endometriosis in seven cases, using antibodies to Ki-67 protein (growth fraction (GF) quantified using a point score method) and oestrogen receptor and progesterone receptor (quantified using the H score method). RESULTS: There was no evidence of a significant difference in the Ki-67 protein, oestrogen receptor, and progesterone receptor in the rete ovarii in different phases of the menstrual cycle (proliferative phase: GF = 1.052, oestrogen receptor H score = 13.4, progesterone receptor H score = 15.32; secretory phase: GF = 0.736, oestrogen receptor H score = 7.5, progesterone receptor H score = 1.84). The expression of all three proteins was greater in the foci of endometriosis (GF = 6.99, oestrogen receptor H score = 152.02, progesterone receptor H score = 127.36) than in the rete ovarii (p < 0.0005-0.0008, Mann-Whitney U test). CONCLUSIONS: There is a low rate of cellular proliferation in the rete ovarii and this structure shows less responsiveness to hormone stimulation than foci of endometriosis. These differences may provide a useful tool to distinguish the rete ovarii from endometriosis in cases of diagnostic difficulty.

Endometriosis↗
PubMed1999

An experimental rat model of salt-sensitive hypertension; biochemical and morphological parameters and sympathetic nervous system.

The objective of the study was to outline the characteristics of the development of hypertension and some neurohumoral, haematological and morphological factors contributing to development of high blood pressure in a genetic model of salt-sensitive rat. Characteristics of Dahl salt-sensitive (DS) rats, as compared to their Dahl salt-resistant (DR) controls were as follows: 1) DS rats display higher blood pressure and lower heart rate compared to DR rats as early as 1 month of age at weaning). They gradually develop hypertension at 2 months of age, irrespective of diet. Low-Na diet (0.5% NaCl) does not prevent hypertension but delays its development and ameliorates it. High Na-diet (8% NaCl) exacerbates hypertension. 2) DS rats have retardation in body weight gain. They develop mild hypochromic anaemia. 3) After 2 months of Na loading (3 months of age), DS rats express significantly increased Na and water retention and increased plasma volume by 15% compared to 2.8% increase in DR rats on high-Na diet. 4) DS rats showed renal parenchymal lesions, more pronounced after Na-loading, focal atrophy of cortical tubules, mesangial matrix expansion and glomerulosclerosis. Consistent with high blood pressure were changes in renal arterioles, fibromuscular proliferation, deposition of fibrinoid material in intima. 5) Sodium loading produced increased activity of the sympathetic nervous system (SNS), and sodium restriction reduced SNS responsiveness.

Animals↗