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P K Paul

Publications and source records attributed to P K Paul.

At least 19 recordsLinked to original sources
PubMed2006

Role of microenvironment in the mixed Langmuir-Blodgett films.

This paper reports the pi-A isotherms and spectroscopic characteristics of mixed Langmuir and Langmuir-Blodgett (LB) films of nonamphiphilic carbazole (CA) molecules mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). pi-A isotherm studies of mixed monolayer as well as the remarkable change in collapse pressure of the mixed monolayer isotherms definitely show that CA is incorporated into PMMA and SA matrices. However, CA is stacked in the PMMA/SA chains and forms microcrystalline aggregates, as is evidenced from the scanning electron micrograph picture. The nature of these aggregated species in the mixed LB films has been revealed by UV-vis absorption and fluorescence spectroscopic studies. The presence of two different kinds of band systems in the fluorescence spectra of the mixed LB films have been observed. This may be due to the formation of low-dimensional aggregates in the mixed LB films. Intensity distribution of different band systems is highly sensitive to the microenvironment of two different matrices as well as also on the film thickness.

Journal Article↗
PubMed1997

Regulatory role of cortisone and dietary carbohydrate energy in prepubertal rat mammary gland growth and development.

Role of cortisone and regulated carbohydrate energy in mammary gland growth, based on studies of morphometric and certain growth and energy related biochemical parameters has been evaluated in the adrenalectomized prepubertal female rat. Results showed improvement or restoration of mammary features like fat pad weight, area, duct system and sprouting of end and lateral buds by cortisone treatment from adrenalectomy induced suppressed state. Similarly the hormone rectified the gland nucleic acids, glycogen and rate of tissue oxidation of glucose levels, reduced under adrenalectomy. Adrenalectomy caused loss of appetite (33.5% less than normal intake). This amount of diet restriction to normal intact did not affect the gland morphology but reduced nucleic acids, protein, glycogen and glucose oxidation rate. Provision of dextrose mixed diet to the adrenalectomized rats showed variable improvements of these biochemical parameters except the gland protein level in association with increase in appetite. However, cortisone therapy under provision of dextrose supply, restored gland protein level and increased further in nucleic acids, glycogen and glucose oxidation rate. The morphological growth parameters with dextrose and cortisone also showed further improvements. Results suggested that glucocorticoid was essential mammary growth factor during prepubertal ages. The hormone appeared to operate via tissue metabolism and stimulating energy intake through appetite stimulation.

Adrenalectomy↗
PubMed1997

Effect of vitamin A excess on germ cell development in prepubertal rat testis.

Vitamin A in graded doses of 125, 250 and 375 U.S.P./kg body wt, po, for 10 days (d 21-30) drastically reduced the testicular weight by 25 to 62% and seminiferous tubular diameter by 14 to 35% in prepubertal rats in lowest and highest doses of the treatment. The treatment induced disproportionate enlargement of nuclei and cytoplasm of the germ cells; predominantly the preleptotene and pachytene spermatocytes. These abnormal germ cells, often with 2 or 3 nuclei displayed vacuolated cytoplasm surrounding pyknotic or granulated or dispersed chromatin granules within the nuclei in a dose proportionate manner. The round spermatids were the most sensitive cell types which completely disappeared in two higher doses of treatment. Vacuolation of Sertoli cell cytoplasm in about 25% of the tubules with associated increase in intertubular space was also observed in rats treated with the highest dose of the vitamin. Circulatory levels of FSH, LH and testosterone remained unaltered following the vitamin excess treatment. Therefore, it is suggested that excess vitamin A even for shorter duration like the present one is detrimental to developing cell types and prevents the progress of the spermatogenic process beyond the round spermatid stage.

Animals↗
PubMed1994

Role of adrenal in establishment and development of conceptus in unilaterally ovariectomized mated rats.

The model of unilateral ovariectomy induced ovarian compensatory hypertrophy in mated bilaterally adrenalectomized rats was used to assess the role of adrenal in conceptus development. Replacement dose of dehydroepiandrosterone (DHA) or corticosterone (Comp. B) from day 2-14 post coitum was given with or without ip injections of estrogen (E, on day 2) and progesterone (P, on day 3 or 3-9). Replacement of adrenal hormones failed to support ipsilateral uterine horn (IP) pregnancy. But injections of E2 and P support IH pregnancy in variable percentages (about 38-75%) of rats depending on the type of adrenal steroids and single or multiple doses of P. Contralateral horn (CH) pregnancy developed under any of these conditions. Adrenalectomy induced reduction of fetal weight and pregnancy index (No. of fetus divided by No. of implantation sites), were not significantly improved by adrenal hormone replacement, except pregnancy index of those animals which received Comp. B and P. Adrenalectomy inhibited compensatory increase of contralateral corpus luteum (CL) volume and ovarian delta 5(3)beta-hydroxy steroid dehydrogenase (delta 5(3)beta-HSD) activity. Replacement of DHA or Comp. B induced these compensatory changes. Comp. B and P appears to be a better combination in establishment of IH pregnancy, pregnancy index maintenance and stimulation of ovarian compensatory changes. Results suggest that adrenocorticoids were not obligatory for conceptus development but were important for efficient action of ovarian steroids in establishment and maintenance of pregnancy. Relationship between nutrition or pituitary gonadotropins and adrenal steroids, having relevance to conceptus development has been discussed.

Adrenal Glands↗
PubMed1993

Comparison of magnetic resonance imaging (MRI) and histopathology in rabbit models of osteoarthritis and immune arthritis.

Osteoarthritis was surgically induced in mature male Dutch Belted rabbits by sectioning the fibular collateral and sesamoid ligaments and removal of the anterior horn of the lateral meniscus. The site of surgical intervention was detectable by MRI. Histopathologic analysis revealed severe focal cartilage lesions on opposing surfaces of the tibia and femur. Histology of cartilage adjacent to the osteoarthritic lesions appeared normal. In another animal model, arthritis was induced by immunization against ovalbumin followed by intra-articular injection of ovalbumin. MRI of immune arthritic rabbit knees showed accumulation of synovial fluid and cartilage degradation. Histopathology was characterized by vascular necrosis of the synovium and depletion of cartilage proteoglycan. MRI can be used to non-invasively follow the therapeutic effects of drug treatment on synovial inflammation and cartilage degradation in rabbit knees.

Animals↗
PubMed1993

Magnetic resonance imaging and morphometric quantitation of cartilage histology after chronic infusion of interleukin 1 in rabbit knees.

Cartilage pathology in rabbit knees was monitored by noninvasive magnetic resonance imaging (MRI) and evaluated using morphometric histologic measurements. Infusion of rabbit knees with the cytokine interleukin 1 induces cartilage degradation and inflammation. A miniosmotic pump was implanted subcutaneously to deliver interleukin 1 through a polyethylene catheter inserted into the rabbit knee. Rabbit knees were imaged using MRI and prepared for histologic examination at 5 and 12 days after chronic infusion of interleukin 1. MRI obtained 0.7-mm sections for three-dimensional reconstruction of cartilage image. Cartilage deterioration near the site of infusion was visible on MRI. MRI measurements indicated a reduction in cartilage thickness. Histology revealed a loss of staining of cartilage matrix proteoglycan, synovial hypertrophy, and perichondral bone resorption. Morphometric analysis of cartilage histology indicated a reduction in both cellularity (chondrocytes/m mu 2 area) and cell to matrix area ratio. These observations suggest that a loss of proteoglycan, an early event in cartilage degeneration, can be detected by MRI.

Animals↗
PubMed1993

Need of dietary energy at critical implantation time when local ovarian hormones are obligatory for conceptus development.

Role of dietary energy and local ovarian hormones in conceptus development in the rat was evaluated by giving ip injections of estrogen and progesterone under diet restricted and/or dextrose supplemented conditions, using the experimental model of ovarian compensatory hypertrophy. Replacement of estrogen on day 2 and progesterone on day 3 was necessary for conceptus development in the ipsilateral uterine horn after unilateral ovariectomy on day 2. Continuation of progesterone injection up to day 9 improved the percentage of conceptus development. Conceptus development was normal when unilateral ovariectomy was performed after day 2 of pregnancy. Compensatory increases in corpus luteum (CL) volume and the activity of delta 5 3 beta-hydroxy steroid dehydrogenase (3 beta-HSD) in contralateral ovary were observed after unilateral ovariectomy on day 2-4 of pregnancy. However, 70% diet restriction reducing the energy intake (from 90 to 27 kcal/rat/day) abolished the single dose hormone therapy effects in ipsilateral horn conceptus development and also reduced the effects of continued progesterone, percentage of contralateral horn conceptus development, compensatory changes in the CL volume and delta 5 3 beta-HSD activity of the contralateral ovary. However, dietary dextrose supplementation (increasing calorie intake from 27 to 56 kcal/rat/day) significantly improved/restored hormone response for conceptus development, compensatory changes of the CL volume and enzyme activity in contralateral ovary. The results suggest that day 2-3 of pregnancy is the critical time when local ovarian supply of estrogen and progesterone are obligatory for establishment and conceptus development in the rat. During this period adequate mobilizable source of energy is necessary for execution of hormonal message.

3-Hydroxysteroid Dehydrogenases↗
PubMed1992

Conformational studies on beta-bend containing a cis peptide unit.

Conformational studies have been carried out on the X-cis-Pro tripeptide system (a system of three linked peptide units, in the trans-cis-trans configuration) using energy minimization techniques. For X, residues Gly, L-Ala, D-Ala and L-Pro have been used. The energy minima have been classified into different groups based upon the conformational similarity. There are 15, 20, 18 and 6 minima that are possible for the four cases respectively and these fall into 11 different groups. A study of these minima shows that, (i) some minima contain hydrogen bonds--either 4-->1 or 1-->2 type, (ii) the low energy minima qualify themselves as bend conformations, (iii) cis' and trans' conformations are possible for the prolyl residue as also the C gamma-endo and C gamma-exo puckerings, and (iv) for Pro-cis-Pro, cis' at the first prolyl residue is ruled out, due to the high energy. The available crystal structure data on proteins and peptides, containing cis-Pro segment have been examined with a view to find the minima that occur in solid state. The data from protein show that they fall under two groups. The conformation at X in X-cis-Pro is near extended when it is a non-glycyl residue. In both peptides and proteins there exists a preference for trans' conformation at prolyl residue over cis' when X is a non-glycyl residue. The minima obtained can be useful in modelling studies.

Alanine↗
PubMed1991

Magnetic resonance imaging reflects cartilage proteoglycan degradation in the rabbit knee.

Cartilage degeneration in osteoarthritis is initiated by a loss of proteoglycan. Intra-articular injection of papain causes a reversible loss of proteoglycan in rabbit knees. Rabbits were scanned with magnetic resonance imaging (MRI), using a 1.5T Signa superconducting magnet with 3 inch surface coil. Spin echo sequences were performed in the coronal and sagittal planes at 0, 24, 48, and 72 h after intra-articular injection of papain to obtain T1, proton density, and T2-weighted images. Cartilage proteoglycan content was measured biochemically and histochemically. Reduced articular cartilage thickness in the MR images of papain-treated knees corresponded to changes in cartilage proteoglycan content.

Animals↗
PubMed1991

Magnetic resonance imaging of the rabbit knee: detection of cartilage proteoglycan degradation.

Intra-articular (i.a.) injection of papain causes a reversible loss of proteoglycan in intact rabbit knees. Twelve rabbits were scanned with magnetic resonance imaging (MRI) at 0, 24, 48 and 72 hours after 5 units of papain i.a. in a 1.5 Tesla Signa with a three inch surface coil using spin echo sequence. Total cartilage thickness in proton density images was 1.08 +/- 0.09 mm prior to papain injection. The magnetic resonance images showed a reduction in articular cartilage thickness in papain-treated rabbit femurs at 24 hours to 0.69 +/- 0.18 mm and partial restoration by 72 hours to 0.77 +/- 0.21 mm.

Animals↗
PubMed1991

Involvement of dietary glucose in adrenal steroidal regulation of spermatogenic and steroidogenic activities in prepubertal rat testis.

Effects of dietary and supplemented dextrose energy on the role of corticosterone (Comp. B) or dehydroepiandrosterone (DHA) in spermatogenic and steroidogenic activity in the bilaterally adrenalectomised prepubertal rat testis were studied. Adrenalectomy reduced the body and testis weight, numbers of the stage VII cell types [spermatogonia A (A), preleptotene (PL) and pachytene (P) spermatocytes and step 7 spermatid (7)], testicular delta 5-3 beta-hydroxysteroid dehydrogenase (delta 5-3 beta-OH-SDH) activity and serum testosterone. Adrenalectomy also caused reduction of energy intake due to loss of appetite which was stimulated by hormone replacement therapy. Treatment of adrenalectomised rats with DNA or corticosterone enhanced the spermatocyte population and the enzyme activity, especially after 30 days of age. Dextrose supplementation with hormone treatment however, did not produce significant additive effect on stage VII cell counts, but delta 5-3 beta-OH-SDH activity showed additive effect in this age group. Results suggest that adrenal steroids regulate testicular steroidogenesis and spermatogenesis during the prepubertal ages by modifying the supply of dietary glucose.

Adrenalectomy↗
PubMed1990

Melanin-concentrating hormone: a structural and conformational study based on synthesis, biological activity, high-field NMR, and molecular modeling techniques.

A series of Melanin-concentrating hormone (MCH) fragments have been synthesized and their biological activities compared with the parent peptide. The substructural units, 5-14 linear and 5-14 cyclic, have been used as models for MCH-- H-Asp1-Thr-Met-Arg-Cys-Met-Val-Gly-Arg HO-Val17-Glu-Trp-Cys-Pro-Arg-Tyr-Val in 1H-nmr conformational studies. Conformational features predicted by molecular dynamics analyses find support in the nmr experiments.

Amino Acid Sequence↗
PubMed1990

Accessible conformations of melanin-concentrating hormone: a molecular dynamics approach.

Molecular dynamics simulations have been used to search for the accessible conformations of the melanin-concentrating hormone (MCH). The studies have been performed on native MCH and two of its peptide fragments, a cyclic MCH(5-14) fragment and a linear MCH(5-14) fragment. An analysis of the molecular dynamics trajectories of the three peptides indicates that two regions of the peptide have characteristic conformational properties that may be important for the biological activity. One is a region around Gly8, which is conformationally mobile, and the other is around Pro13, which shows unusual rigidity. The molecular dynamics simulation results are discussed in terms of backbone structural features like beta turns, side-chain interactions, and orientations of the disulfide bridge. The results of this analysis are used to suggest new analogues that will modify the conformational features of the peptide and further define the conformational requirements for activity. Finally, the results are related to nmr studies of the peptide and reveal agreements between the experimental nuclear Overhauser effect constraints and some of the accessible conformations obtained from the simulation.

Amino Acid Sequence↗
PubMed1990

The conformational preferences of gamma-lactam and its role in constraining peptide structure.

The conformational constraints imposed by gamma-lactams in peptides have been studied using valence force field energy calculations and flexible geometry maps. It has been found that while cyclisation restrains the psi of the lactam, non-bonded interactions contribute to the constraints on psi of the lactam. The gamma-lactam also affects the (psi, psi) of the residue after it in a peptide sequence. For an L-lactam, the ring geometry restricts psi to about -120 degrees, and psi has two minima, the lowest energy around -140 degrees and a higher minimum (5 kcal/mol higher) at 60 degrees, making an L-gamma-lactam more favourably accommodated in a near extended conformation than in position 2 of a type II' beta-turn. The energy of the psi approximately +60 degrees minimum can be lowered substantially until it is more favoured than the -140 degrees minimum by progressive substitution of bulkier groups on the amide N of the L-gamma-lactam. The (psi, psi) maps of the residue succeeding a gamma-lactam show subtle differences from those of standard N-methylated residues. The dependence of the constraints on the chirality of gamma-lactams and N-substituted gamma-lactams, in terms of the formation of secondary structures like beta-turns is discussed and the comparison of the theoretical conformations with experimental results is highlighted.

Computer Simulation↗
PubMed1989

A novel beta-turn location in an LHRH antagonist: a combined conformational search and molecular dynamics study.

A 50 pico-second molecular dynamics simulation on a cyclic LHRH antagonist analogue Ac-D-Phe1-D-Phe2-D-Trp3-Ser4-Glu5-D-Arg6-Leu7-Lys8+ ++-Pro9-D-Ala10-NH2 (where the cyclisation is via an amide linkage between the Glu5 and Lys8 side chains), reveals some hitherto unseen conformational features. The LHRH analogue is found to adopt a near beta-sheet type of conformation with the reversal in the chain being brought about by a D-Trp3-Ser4-Glu5-D-Arg6 beta turn. The N- and C-terminal ends of the peptide come close together and interact through a network of hydrogen bonds. Additional hydrogen bonds expected of a sheet type of conformation stabilise the lowest energy minima. A conformational search of all possible cyclic structures of a model system c(Glu-D-Ala-Ala-Lys) which was used to determine the starting structure for the simulation studies of the cyclic LHRH antagonist analogue is also highlighted. The influence of the cyclic part on the conformation of this LHRH analogue is discussed.

Amino Acid Sequence↗
PubMed1988

Computerized 3-D reconstruction of small blood vessels from high voltage electron-micrographs of thick serial cross sections.

Morphological analysis of compartments in terms of volumes and the orientation of the cells and their nuclei within very small mesenteric arteries and arterioles is being carried out. Samples were from simultaneously sham operated and instrumented control and one-clip two kidney Goldblatt sustained (30 days) hypertensive dogs. Collection of specimens was standardized, i.e. sampling location, perfusion fixation, embedding, staining, and sectioning by methods proven to preserve in vivo dimensions. Serial thick cross sections (0.5 mu) were subjected to high voltage electromicrography (1.0 MeV) at 2500x and then linearly enlarged 3x photographically. The glossy micrographs (7500x) were made into montages and the contours of the smooth muscle layer (vascular smooth muscle), the endothelium (E), nuclei (N), and the internal lamina (IL) were digitized on a large GTCO digi-pad with input to a microcomputer (PC-Limited, Turbo) equipped with a 20 MB hard disk and coprocessor. Solid and transparent image reconstructions and computerized dissection of cell compartments were performed. Compartment volumes of vascular smooth muscle, IL, E and N, and individual cell and nuclear volumes, as well as nuclear/cytoplasmic ratios were calculated. Image reconstructions are presented. The emphasis is on methods and these are discussed in terms of useability for determining accurate microvessel morphology in health and disease, with particular emphasis on assessment of hypertrophy and hyperplasia in experimental hypertension, and architectural angiogenesis in general.

Animals↗