Biomedical subjects

S Majumdar

Publications and source records attributed to S Majumdar.

At least 271 records · Page 15Linked to original sources

PubMed1990

Effect of verapamil on different spermatozoal functions in guinea pigs--a preliminary study.

Verapamil, a calcium channel blocker, was administered orally using three different doses to guinea pigs. Both short-term (4 weeks) and long-term (12 weeks) effects of the drug were observed. The drug administration resulted in a marked decrease in sperm density, sperm motility and cellular energy content (ATP). Zona pellucida penetration by the sperm obtained from drug-treated animals was significantly lower when compared with sperm from normal animals. Histopathological findings exhibited partial arrest of spermatogenesis. Partial to complete recovery was observed after 4 and 6 weeks of withdrawal of the drug treatment.

Adenosine Triphosphate↗

PubMed1990

Pharmacokinetics of superparamagnetic iron-oxide MR contrast agents in the rat.

The in vivo pharmacokinetics and the biodistribution of superparamagnetic iron-oxide particles (AMI25, Advanced Magnetics, Cambridge, MA) were investigated in anesthetized rats. Four different dose concentrations, ranging from 49.8 to 408.9 mumol of Fe (or 2.78-22.84 mg Fe) per kilogram, radiolabeled with 6.0 microCi of 59Fe-AMI25 were injected intravenously into 18 rats. The radioactivity cleared from the circulation with a fast component with a half-life of approximately 10 minutes and a slower component with a half-life of 92 minutes. Both half-lives were independent of the injected dose (ID) in the range of 105.4-408.9 mumol (5.89-22.84 mg) Fe/kg. The relative uptake in the liver, spleen, and kidneys was 57%, 2.9%, and 2.0% of the ID, respectively. At a dose of 52.1 mumol (2.91 mg) of Fe/kg, the relative concentration of iron significantly increased in the liver and decreased in the blood. Within the kidney, autoradiography showed that the iron was selectively taken up by the cortex. In the kidney, a concentration of 0.23 mumol (0.013 mg) Fe/g resulted in a 30% reduction in image intensity in a single echo magnetic resonance image obtained using a spin-echo sequence and an echo time of 70 ms.

Animals↗

PubMed1990

Correlation between human placental lactogen levels and glucose metabolism in pregnant women with intrauterine growth retardation.

Twenty pregnant women with fetal growth retardation and 20 pregnant women with appropriate for gestational age fetuses (controls) were recruited after the 28th week of gestation. Samples were collected for estimation of serum insulin and human placental lactogen (HPL) levels in the fasting state and a glucose tolerance test was carried out on all the subjects. The results showed the glucose and HPL levels to be significantly lower in the fetal growth retardation group compared to controls. There were no differences in the fasting serum insulin levels in the 2 groups. Fetal growth retardation appears to be linked with the absence of development of the physiological 'diabetogenic' state in the second half of pregnancy. This maternal hypoglycaemic state is associated with low HPL levels and not with raised maternal insulin levels as measured in the fasting state.

Adult↗

PubMed1990

Short-term therapy of atherosclerosis with low dose indomethacin: an experimental study.

The effects of low dose indomethacin therapy in primary prevention of diet-induced atherosclerosis of rhesus monkeys was studied. The parameters studied were serum cholesterol concentration, thromboxane A2 (T x B2), prostacyclin (6-keto-PGF1 alpha) in serum/plasma, and the extent and intensity of coronary atherosclerosis. Although indomethacin did not affect serum cholesterol, it reduced serum T x B2 significantly (P less than 0.01). Plasma 6-keto-PGF1 alpha was not restored to the pretreatment level. A significant protective role of the drug was noted as far as coronary atherosclerosis is concerned (P less than 0.01).

6-Ketoprostaglandin F1 alpha↗

PubMed1990

Effect of various doses of medroxyprogesterone acetate on intestinal functions in rats.

The dose relationship between medroxyprogesterone acetate (MPA), a long acting contraceptive, and rat intestinal digestive and absorptive functions has been investigated. The study revealed that the activities of brush border sucrase, lactase and leucine aminopeptidase were stimulated only at high doses, viz 70 mg/kg (180 mumol/kg) body weight and above, whereas the activity of alkaline phosphate was depressed at comparatively low dose (17.5 mg/kg; 45 mumol/kg body weight). This decrease was found to be significant (p less than 0.001) at all the doses tested. The inhibition in the intestinal uptake of calcium paralleled the decrease in alkaline phosphatase activity. Relatively high amount of MPA (140 mg/kg; 360 mumol/kg) was required to augment the uptake of glucose and amino acid. The results obtained do not indicate a close relationship between the dose of the drug and the extent of alteration in the rat intestinal digestive and absorptive functions. The study appears to confirm the association between brush border enzymes activities and uptake of nutrients in rat intestine.

Animals↗

PubMed1990

Sequential isolation and biochemical analysis of pulmonary surfactant from human lung homogenate.

Pulmonary surfactant was isolated from human lung homogenate after differential and sucrose density gradient centrifugation. Purification of the isolated material was ascertained by electron microscopy and alkaline phosphatase (AKP) specific activity. Elevated levels of phospholipid/protein ration and AKP specific activity were observed in the purified material when monitored at different stages of purification. Biochemical analysis of the isolated material showed that it consisted of 74.08% lipid, 19.06% protein and relatively smaller amounts of nucleic acids, sialic acid and hexoses. Phosphatidyl choline was the predominant phospholipid whereas triglycerides and cholesterol levels were high among neutral lipids. Gas liquid chromatography of the material showed palmitic acid (16:0) as the major saturated fatty acid. These findings indicated that a large scale isolation of surfactant might be possible and utilized for therapeutic treatment of neonatal respiratory distress syndrome.

Adult↗

PubMed1989

Ligand-induced dimerization of the platelet-derived growth factor receptor. Monomer-dimer interconversion occurs independent of receptor phosphorylation.

The platelet-derived growth factor (PDGF) receptor is a single membrane-spanning polypeptide of 180,000 daltons with a ligand-stimulatable tyrosine kinase site. We have investigated changes in the structure and association state of the receptor that are induced by ligand binding, but which precede autophosphorylation. Chemical cross-linking of PDGF-bound 32P-labeled receptor and 125I-PDGF-labeled receptor resulted in the generation of a radiolabeled cross-linked complex of 370-390 kDa. This band, as well as the 180-190-kDa PDGF receptor band, were recognized by a PDGF receptor-specific antipeptide antibody. The appearance of the 370-390-kDa band was PDGF-dependent and was seen irrespective of whether the receptor was membrane-bound, solubilized, or highly (approximately 90%) purified. Sedimentation analysis of the 125I-PDGF cross-linked receptor showed that both 180-190- and 370-390-kDa labeled species sedimented as a single peak at about 11.5 S, a position expected of a receptor dimer, demonstrating that the liganded receptor exists essentially as a dimer. In contrast, unliganded receptors sedimented as a single species at 7 S, a position consistent with a monomeric structure. The monomer-dimer interconversion was absolutely ligand-dependent and occurred independent of autophosphorylation. These results demonstrate and intimate correlation between PDGF binding and inter-receptor bond formation, and raise the possibility that the phenomenon may be causally linked to the process of kinase activation.

Affinity Labels↗

PubMed1989

Glucose-6-phosphate phosphohydrolase activity in guinea pig liver microsomes is influenced by phosphatidylcholine. Interaction with cholesterol-enriched membranes.

Guinea pig liver microsomal membranes were cholesterol-enriched by feeding guinea pigs a high-cholesterol diet. Cholesterol enrichment as well as partial lipid removal of normal native microsomes by acetone-butanol extraction resulted in 40-50% loss in activity of the glucose-6-phosphate phosphohydrolase (G-6-Pase) (EC 3.1.3.9) enzyme system. The activity was restored by supplementation of microsomal total phospholipid (PL) and its phosphatidylcholine (PC) species but not with microsomal neutral lipids, cholesterol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, sphingomyelin or diphosphatidylglycerol (cardiolipin). The activity was decreased by sodium deoxycholate but enhanced by dimethylsulfoxide. Egg-yolk PC and asolectin influenced the activity of the enzyme to the same extent as microsomal PC did. Lipid depletion and cholesterol produced an increase in Km while the Vmax was lowered. The non-linearity in the Arrhenius plot of the native microsomes was lost on lipid removal and cholesterol enrichment. The energy of activation (Ea) calculated from the continuous line was found to be lowered to the level that was observed above the break points in intact microsomes. Addition of microsomal PC to the assay system decreased the Km of the enzymatic reaction in native membranes, in partially lipid-depleted and cholesterol-enriched membranes, but did not alter the Vmax values and only marginally influenced the non-linear relationship of the Arrhenius expression of temperature dependence. The ability of immature rat liver phospholipid exchange protein to introduce alien PL into microsomal membrane was used to study the lipid dependence of G-6-Pase. Protein-catalyzed and detergent (cholate)-mediated membrane PL exchange for egg-yolk PC from the PC/cholesterol unilamellar liposomes resulted in substantial loss of enzyme activity. The discrepancies in the influence of PC on G-6-Pase were interpreted by assuming that the enzyme was a two-component system, a surface-located substrate transporter unit and a membrane integral catalytic phosphohydrolase unit. The lipid microenvironment and PL requirement in particular, could be different for the two components, although they represented a single functional unit at the time of enzymatic reaction.

Animals↗

PubMed1989

A quantitative study of relaxation rate enhancement produced by iron oxide particles in polyacrylamide gels and tissue.

The proton relaxation rate enhancements produced by two types of iron oxide particles, M4125 and AM125 (Advanced Magnetics, Cambridge, MA) designed as potential MR contrast agents, have been measured in polyacrylamide gels and in liver and spleen. The organ uptakes, time courses, and biodistributions of these materials have been measured using radiolabeling. The relaxation rate enhancements produced by these particles have been related to the concentration of iron per gram material at different magnetic field strengths. The relaxation rates increase linearly as a function of concentration at field strengths varying from 0.15 to 7 T. The relaxation effects of these particles in tissue are significantly different from the behavior in vitro. These results suggest that several different mechanisms contribute to relaxation effects in the presence of iron oxide particles and they depend strongly on the way the particles are sequestered. Diffusion effects for a specified TE may be enhanced using gradient or single-spin echoes rather than multiple echoes. AM125 is significantly more effective as a relaxation agent than paramagnetic metal ions only at relatively high fields, while M4125 is less effective per unit concentration.

Acrylic Resins↗

PubMed1989

The influence of pulse sequence on the relaxation effects of superparamagnetic iron oxide contrast agents.

The effects of different pulse sequences and timing parameters on the increase in transverse relaxation rate produced by superparamagnetic iron oxide particles have been studied. Gradient-echo, single spin-echo, and multiple-echo images recorded at 2.0 T were used to evaluate the reduction in signal intensity per unit concentration of iron oxide for different echo times and in different media. For the same echo time, gradient-echo sequences were found to be more than twice as sensitive to the effects of the agent as single spin-echo imaging sequences, while multiple-echo sequences were much less affected than either. Using measurements of the relative effects on different sequences, the contributions of different relaxation mechanisms have been quantified.

Contrast Media↗

PubMed1989

Gossypol inhibition of Ca++ uptake and Ca++-ATPase in human ejaculated spermatozoal plasma membrane vesicles.

Gossypol, a plant-derived polyphenolic compound known to exert contraceptive actions in men, inhibits Ca++-transport and Ca++-activated ATPase in isolated plasma membranes of ejaculated human sperm cells. It also inhibits the membrane bound Mg++- and Na+ + K+-dependent ATPases, 5'-nucleotidase and alkaline phosphatase systems. Ca++-ATPase inhibition by gossypol is non-competitive. It abolishes the discontinuity in Arrhenius expression of temperature dependence of Ca++-ATPase and increases the energy of activation. Phosphatidyl choline and Na+-deoxycholate inhibit Ca++-transport activity in the membrane vesicles. The apparent similarity of Ca++-transport inhibition by gossypol and phosphatidyl choline may indicate the possible capability of this compound to induce changes in the lipid microenvironment of the membranes, wherein the integral proteins operate. Inhibitory effect of gossypol on the plasma membrane Ca++-pump suggests that gossypol may affect sperm motility by a mechanism which is related to the structure and functions of the plasma membrane.

5'-Nucleotidase↗

PubMed1989

Kinetics of oral propylene glycol-induced acute hyperlactatemia.

The kinetics of PD-induced HL in rat have been investigated. The data obtained indicated that PD was solely responsible for the elevation (1.83- to 4.01-fold) of blood lactate that was sustained long enough to affect considerably the normal physiological function of the system. The production of lactate increased as the dose of PD increased up to 38.66 mmole/kg, thereby obeying the Michaelis-Menten kinetics model that gave an apparent Km and Vmax as 7.14 mmole/kg and 7.50 mmole/liter/hr, respectively. The t1/2 elimination time ranged from 1.40 to 5.82 hr which followed apparent first-order kinetics. Pyrazole inhibited (Ki = 6 mumole/kg) the PD-induced HL competitively, suggesting that alcohol dehydrogenase might have played a regulatory role in the conversion of PD to lactate. The PD-induced HL in rat and the LA in human patients are two distinct biochemical entities; reasoning has been given to substantiate that HL is lower order LA. Evidence has been presented to show that PD is a suitable and effective potential agent for producing experimental HL in rat in preference to agents that are currently being used.

Alcohol Dehydrogenase↗

PubMed1989

Contrast and accuracy of relaxation time measurements in acquired and synthesized multislice magnetic resonance images.

The effects of interslice spacing, the number of data points and other factors on the accuracy of relaxation time measurements and contrast have been investigated for both acquired and synthesized multislice MR images using experiments and computer simulations. The cross-excitation between adjacent slices in multislice imaging affects both contrast and derived relaxation times. Such measurements also are affected by the T1 and T2 of the materials imaged, the pulse sequence timing parameters, and the number of data points used to estimate the relaxation times. Errors in T1 and T2 may be severe, particularly for slice spacings less than 0.5 slice thickness and for long T1 and T2 materials. Consequently, the difference in signal intensities between two materials with different relaxation times also varies with slice spacing and between acquired and synthetic images, particularly for strongly T1-weighed images.

Computer Simulation↗

PubMed1989

Empirical classification of speech/language impairment in children. I. Identification of speech/language categories.

Cluster analysis was employed to classify speech/language impairment in a sample of 347 children 5 years of age. Based on scores on a variety of speech and language tests, four groups of children with similar linguistic profiles were identified. These groups were labeled high overall, low overall, poor auditory comprehension, and poor articulation. Differences among these groups according to cognitive, developmental, demographic, and audiometry variables were examined. The low overall group was most disadvantaged on all measures, the high overall group was most advantaged, and the poor articulation and poor auditory comprehension groups were intermediate. The implications of these findings for the development of a theory of the relationship between speech/language and psychiatric disorders are discussed.

Articulation Disorders↗

PubMed1989

The activities of phosphatases and aminotransferases in the epithelium of the small intestine and caecum of white rock cockerels during starvation.

Alkaline phosphatase (ALP, EC 3.1.3.1), acid phosphatase (ACP, EC 3.1.3.2), aspartate aminotransferase (ASAT, EC 2.6.1.1) and alanine aminotransferase (ALAT, EC 2.6.1.2) were measured in the mucosal homogenates of the duodenum, jejunum and caecum of full-fed (control), starved and refed White Rock Cockerels. Starvation caused a significant (p less than or equal to 0.05) increase in the activity of ACP in all three segments of the intestine. Subsequent re-feeding brought the activity back to the control level. In contrast ALP activity fell in the duodenum during starvation and was partially restored by refeeding. In the jejunum and caecum the ALP activity decreased during starvation and was fully restored by re-feeding only in the caecum. ASAT activity increased (p less than or equal to 0.05) during the entire period of starvation in all three segments. Re-feeding failed to decrease the enzyme activity within 48 hours. Starvation caused a reduction (p less than or equal to 0.05) in the activity of ALAT and re-feeding did not increase the activity in the duodenum and jejunum. The caecum showed no change in the activity during fasting.

Animals↗

PubMed1989

Uterine junctional zone: MR study of water content and relaxation properties.

Weighted samples of uterine myometrium, junctional zone, and endometrium were excised for determination of T1 and T2 in a 20-MHz spectrometer and then dried for determination of water content. The remainder of each uterus, examined with special histopathologic stains, demonstrated no significant difference in the number of blood vessels, smooth muscle cells, fibroblasts, elastin, iron, collagen, mucin, polysaccharide, or amyloid. The junctional zone water content (79.28%) was significantly lower than that of endometrium (82.88%, P = .004) and myometrium (81.05%, P = .005). The T1 of the junctional zone (ie, 643) was significantly lower than that of endometrium (ie, 836; P = .004) and myometrium (ie, 709; P = .01). The T2 of the junctional zone (ie, 58) was significantly lower than that of endometrium (ie, 87; P = .003) and myometrium (ie, 67; P = .006). The low signal intensity of the junctional zone on T2-weighted MR images is accounted for by its lower water content and T2, while the brightness on T1-weighted images is due to its reduced T1.

Adult↗

PubMed1989

Effect of heat-stable and heat-labile enterotoxins of Escherichia coli on intestinal brush border membrane enzymes of mice.

The activities of intestinal brush border membrane (BBM) enzymes alkaline phosphatase, maltase, lactase, sucrase, gamma-glutamyl transpeptidase and leucine aminopeptidase were determined in intestinal homogenates and purified BBMs from control, heat-stable and heat-labile enterotoxin treated mice. The activities of all the enzymes except lactase were decreased significantly (p less than 0.01) in homogenates while increased significantly (p less than 0.001) in BBMs of experimental groups as compared to controls. Calmodulin activities were increased significantly (p less than 0.01) as compared to control in heat-stable enterotoxin treated mice but remained unaltered in heat-labile enterotoxin treated mice. DNA contents of intestinal homogenates were decreased in experimental groups demonstrating the decrease in cell number in these groups. The altered BBM enzyme activities could not be attributed to changes in calmodulin activities. The increase in enzyme activities in BBMs may reflect a compensatory phenomenon in the remaining cells.

Alkaline Phosphatase↗

PubMed1989

In vitro electrophysiological effects of cimetidine, prostaglandin E2 and acetylcholine on the rabbit gastric mucosa.

The electrophysiological effects of cimetidine, cytoprotective dose of prostaglandin E2 (PGE2) and acetylcholine were determined in parallel in Ussing-chambered rabbit fundic and antral mucosal preparations. In the fundic mucosal preparations both cimetidine and PGE2 caused an increase in transmucosal potential difference (PD) and in short-circuit current (ISC); the transepithelial resistance (Rt) was essentially unchanged. Addition of acetylcholine to the pretreated fundic preparations produced further gradual increases in PD and ISC; cimetidine pretreatment delayed this effect of acetylcholine. In contrast to fundic mucosa, cimetidine did not cause any electrical change of the antral preparation but decreases in PD, Rt and ISC were detected after the addition of PGE2. Acetylcholine produced a rapid initial PD elevation followed by a PD drop of both antral tissues independent of pretreatment. These findings suggest that both cimetidine and PGE2 generated electrical hyperpolarisation of rabbit fundic mucosa. These changes may be favourable for mucosal protection. No "beneficial" electrical changes were detected on the antral mucosa after administration of cimetidine and PGE2. Acetylcholine increased the effects of other stimuli on the fundic mucosa. In the rabbit antral mucosa acetylcholine generated biphasic changes of electrical properties.

Acetylcholine↗