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Biomedical subjects

A Bhattacharya

Publications and source records attributed to A Bhattacharya.

At least 235 records · Page 13Linked to original sources
PubMed1982

Physiologic effects of respirator dead space and resistance loading.

Air-purifying respirators impose several loads on breathing. The effects of inspiratory flow resistance, respiratory dead space such as that of a full-face mask, and moderate exercise and maximal exercise were assessed alone and in combination in nine normal volunteers. There were significant effects on respiratory timing variables (e.g., inspiratory time, inspiratory: expiratory time ratio), peak mouth pressure and peak inspiratory flow rate. Only minimal effects on heart rate were noted. These results suggest that prospective workers who must utilize respirators should be observed during exercise as well as at rest and that a respirator dead space and inspiratory resistance should not produce a significant heart rate change but should lead to adaptation of the inspiratory: expiratory time ratio. Workers who show atypical responses should be assessed particularly carefully.

Adult↗
PubMed1982

A single monoclonal anti-Ia antibody inhibits antigen-specific T cell proliferation controlled by distinct Ir genes mapping in different H-2 I subregions.

A xenogeneic rat anti-mouse Ia monoclonal antibody, M5/114 (gamma 2b, kappa), was studied for its effects in vitro on T cell proliferative responses. Strain distribution studies revealed that M5/114 could inhibit I-A subregion-restricted T cell responses of the H-2b,d,q,u but not the H-2f,k,s haplotypes, indicating that this xenoantibody recognizes a polymorphic determinant on mouse Ia molecules. This same monoclonal antibody was found to inhibit BALB/c (H-2d) T cell proliferation to both G60A30T10 and G58L38 phi 4. The Ir genes regulating responses to these antigens map to either the I-A subregion (GAT), or the I-A and I-E subregions (GL phi), raising the possibility that M5/114 recognizes both I-A and I-E subregion-encoded Ia glycoproteins. It could be shown, using appropriate F1 responding cells, that M5/114 does in fact affect GAT and GL phi responses by interaction with both the I-A and the I-E subregion products, and not by any nonspecific effect resulting from binding to the I-A subregion product alone. These results are consistent with genetic and biochemical studies directly demonstrating that M5/114 recognizes A alpha A beta and E alpha E beta molecular complexes. The existence of a shared epitope on I-A and I-E subregion products suggests the possibility that these molecules arose by gene duplication. Finally, the precise correlation between the Ia molecules recognized by M5/114 and the ability of this antibody to block T cell responses under Ir gene control strengthens the hypothesis that Ia antigens are Ir gene products.

Animals↗
PubMed1981

Membrane modification differentially affects the binding of the lactogenic hormones human growth hormone and ovine prolactin.

Human growth hormone (hGH) and ovine prolactin (oPRL) are both lactogenic as defined by their ability to induce milk-protein synthesis in vitro in the presence of insulin and hydrocortisone. At physiological concentrations, both hGH and oPRL have similar dose-response curves in a mouse mammary gland organ culture system. Binding of 125I-labeled hGH (125I-hGH) to lactogenic receptors is competed by both hGH and oPRL, and the competition curves are nearly superimposable. Moreover, solubilized membrane proteins bound with either 125I-hGH or 125I-labeled oPRL (125I-oPRL) show the same sedimentation pattern on sucrose gradients. However, methylation of membrane phospholipids in the presence of the methyl donor S-adenosyl-L-methionine only increases the binding of 125I-hGH. Binding of either 125I-oPRL or 125I-labeled bovine growth hormone (125I-bGH) was unaffected. Addition of concanavalin A (Con A) to the membranes decreased binding of 125I-oPRL to the lactogenic site by 80%, whereas 125I-hGH binding was decreased by only 40%, with the binding of 125I-bGH unaffected. However, both hGH-and oPRL-bound proteins bind to Con A-Sepharose columns to the same extent. These results suggest that although hGH and oPRL bind to the same lactogenic site with similar affinities and elicit similar biological responses, modification of membranes either by phospholipid methylation or by Con A differentially affects the binding of these two hormones.

Animals↗
PubMed1981

A shared alloantigenic determinant on Ia antigens encoded by the I-A and I-E subregions: evidence for I region gene duplication.

Two monoclonal antibodies to mouse Ia antigens were produced by fusion of xenoimmune rat spleen cells with the NSI myeloma. These monoclonal antibodies detect polymorphic determinants present on B cells and activated T lymphocytes from mice carrying the H-2b, H-2d, H-2k, H-2r, and H-2q haplotypes but not from mice carrying the H-2s or H-2r haplotypes. Antigenic site number determinations showed the positive haplotypes can be divided into 2 groups. Mice bearing the H-2b, H-2d, and H-2q haplotypes express a high number--40,000 to 80,000--of antigenic sites per B lymphocyte, and monoclonal antibody plus complement can lyse B cells from these mice. In contrast, mice bearing the H-2k and H-2r haplotypes express a low number of antigenic sites--about 5000 per cell. Spleen cells from mice carrying the latter haplotypes are not lysed with monoclonal antibody and complement. Genetic mapping demonstrated that high and low expression map to the I-A and I-E subregions, respectively. The monoclonal antibodies detect an Ia specificity on I-Ab, I-Ad, I-Ed, and I-Ek molecules. These observations were confirmed using several different experimental approaches, i.e., cytotoxicity, fluorescent staining, competitive inhibition of monoclonal antibody binding, and 2-dimensional gel electrophoresis of immunoprecipitates. The avidity for A alpha b A beta b and E alpha k E beta k is 5 to 7 x 10(-9) M-1. The antigenic determinant is heat labile, which suggests that it is not carbohydrate. The results imply that Ia antigens encoded by distinct subregions share sequence homology, which may be a consequence of ancestral gene duplication.

Animals↗
PubMed1980

Body acceleration distribution and O2 uptake in humans during running and jumping.

Body acceleration distribution and its relation to the mode of generation were determined in eight young males (19-26 yr) who walked and ran on a treadmill operated at four speeds and jumped on a trampoline at four heights. With increasing treadmill speed, peak acceleration at the ankle (Aa = 3.0-12.0 Gz) always exceeded that at the back and forehead (Ab = 0.9-5.0 Gz, and Ah = 0.8-3.9 Gz); these acceleration profiles included higher frequency components than those during jumping. Corresponding ranges of oxygen uptake (VO2) and heart rate (HR) were 0.8-3.0 l/min and 90-180 beats/min, respectively. With increasing jumping height, acceleration levels were more symmetrically distributed (Aa = 3.0-7.0 Gz, Ab = 3.9-6.0 Gz, and Ah = 3.0-5.6 Gz); VO2 and HR ranges were 1.1-2.5 l/min and 102-175 beats/min, respectively. VO2 was linearly related to HR for both types of exercise. The results indicate that, for similar levels of HR and VO2, the magnitude of the biomechanical stimuli is greater with jumping on a trampoline than with running, a finding that might help identify acceleration parameters needed for the design of remedial procedures to avert deconditioning in persons exposed to weightlessness.

Adult↗
PubMed1979

Phospholipid methylation stimulates lactogenic binding in mouse mammary gland membranes.

Addition of the methyl donor S-adenosyl-L-methionine to membranes prepared from mammary glands of lactating mice results in increased binding of 25I-labeled human growth hormone to the lactogenic receptors. This stimulation is dose dependent and specific for S-adenosyl-L-methionine and is partially inhibited by simultaneous addition of S-adenosyl-homocysteine to the reaction. Pretreatment of the membranes with S-adenosyl-L-methionine for 30 min at 37 degrees C is sufficient to cause enhanced binding. Scatchard analysis shows that treatment with S-adenosyl-L-methionine results in an increase in the number of lactogenic binding sites without changing the apparent affinity constant for 125I-labeled human growth hormone. The increase in the number of binding sites is believed to be due to alteration in the phospholipid composition of the membrane because methylation of phospholipids is observed under these conditions.

Animals↗
PubMed1979

Cardiac responses of dogs to nonsynchronous and heart synchronous whole-body vibration.

Changes in cardiac function produced by synchronizing vibration-induced forces with events in the cardiac cycle were compared to those for the nonsynchronous case in eight chronically instrumented, tranquilized dogs. The supine animals received sinusoidal, whole-body vibration (along the spinal +/- Gz axis) at a constant acceleration amplitude (+/- 0.75 G). The vibration frequency (2-3 Hz) was set equal to the paced heart frequency. Synchronization between vibration and cardiac cycles on a beat-by-beat basis produced a specific and sustained cardiovascular response; such a sustained response was not possible with nonsynchronous vibration. With synchronization, relationships could be found and sustained in which changes either exceeded or were below mean nonsynchronous levels, in some cases below previbration values. For the synchronous vs. nonsynchronous states, significant modification of cardiac function was reflected in parameters such as coronary flow (+15% to -34%) and myocardial oxygen consumption (+21% to -51%). Thus, whole-body oscillation acceleration (vibration) is a forcing function that can produce and maintain a particular cardiovascular response.

Animals↗
PubMed1979

Modification of cardiac function by synchronized oscillating acceleration.

The sensitivity of selected cardiovascular (CV) responses to the physical stressor of External whole-body oscillating Acceleration Synchronized with the Electrocardiogram (EASE) was analyzed in 8 chronically instrumented tranquilized dogs. A sinusoidal acceleration wave form was imposed on the supine animals along the spinal (+/- Gz) axis at a constant amplitude of +/- 0.75 G, and a frequency equal to the paced-heart frequency (2--3 Hz). When the peak force was positive in early systole, and negative in early diastole, changes in myocardial oxygen consumption (MVo2, + 8%), mean coronary flow (MCF, + 8%), stroke volume (SV, + 15%), cardiac work (CW, + 19%) and the time derivative of left ventricular pressure (dP/dt, + 18%) were minimal in comparison to nonoscillatory control values. When the peak force was positive in early diastole and negative in late diastole and early systole, changes in MVo2 (+ 41%), MCF (+ 39%), SV (+ 33%), CW (+ 50%), and dP/dt (+ 31%) were maximal. Thus the capability of EASE to produce a range of desired sustained CV responses provides a basis for its potential diagnostic/therapeutic applications.

Acceleration↗
PubMed1979

Deconditioning-induced exercise responses as influenced by heat acclimation.

Five young men were tested on a bicycle ergometer before (Test 1) and after (Test 2) 8 d of heat acclimation (exercise at 50% of Vo2max at 39.8 degrees C DB, 30.0 degrees C WB) and after 8 h of water immersion (Test 3). A control group of five subjects underwent a similar procedure in a temperate environment of 23.8 degrees C. Heat acclimation resulted in the usual decreases in exercise heart rate (30 beats/min) and rectal temperature (0.6 degrees C) and an increase in sweat rate (19%). The control group showed effects of moderate training by decreases in exercise heart rate (11 beats/min), rectal temperature (0.3 degrees C), and sweat rate (24%). Water immersion resulted in substantial diuresis in both groups, despite 1800 ml of water consumed by each subject. In the acclimation group, exercise responses in Test 2 were better than in Test 1, with little improvement shown by the control group. The acclimation group maintained exercise responses in Test 3 as in Test 1, with more adverse responses shown by the control group. The results show that heat acclimation provides an effective method to prevent the adverse effects of water-immersion deconditioning on exercise tolerance.

Acclimatization↗
PubMed1977

Parameters for assessing vibration-induced cardiovascular responses in awake dogs.

The vibration parameters for assessing the response of the cardiovascular system to whole-body vibration were studied. Six awake, chronically instrumented canines were restrained with their spines vertical, and exposed to GZ sinusoidal vibration of 2-12 HZ for a constant peak acceleration amplitude of +-1.0 G. Vibration exposures of 30 s with intervening recovery periods of 2 min were employed. The following variables were measured: mean heart rate (MHR), stroke volume (SV), mean aortic flow (MAF), mean aortic pressure (MAP), the peak net force transmitted to the canine/body weight (PNF/BW), and the vibration platform frequency (ft), displacement, and acceleration. The percentage change from control (no vibration) of MAF varied linearly with PNF/BW for all cases. MAF also varied linearly with the log MHR/ft for the number of dogs which primarily changed MHR during the vibration exposures. The response of MAP was minimal in all cases, indicating a decrease in total peripheral resistance with increasing PHF.

Animals↗
PubMed1976

Histochemical and biochemical study on acid phosphatase activity in differentiating liver of chick.

1. Acid phosphatase activity at different ontogenetic stages of liver in chick has been studied both by histochemical and quantitative biochemical methods. 2. It has been observed that the activity of acid phosphatase does not remain constant, but undergoes changes at different phases of epigenesis. The activity rhythmically becomes higher and lower throughout the whole period of epigenesis. Comparatively higher activities have been found up to 8 days of incubation, and then the activities become lower up to 14 days and again increased at later periods of development. 3. Higher acid phosphatase activity has been observed in the perivascular connective tissue than the parenchymal cells from the 8th to the 20th day of incubation. 4. The acid phosphatase activity is high in the nuclei of early developing red blood corpuscles, but in advanced stage of R.B.C. the phosphatase activity is very high in the cytoplasm, and it is practically absent in the nuclei. 5. The activity of acid phosphatase may have some relation with the cell death and catabolic processes during chick liver morphogenesis. The relation of the phosphatase activity with the growth and differentiation of the liver has been discussed.

Acid Phosphatase↗