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Biomedical subjects

S Chakravarty

Publications and source records attributed to S Chakravarty.

At least 91 records · Page 5Linked to original sources
PubMed1986

Effect of lindane on eggshell characteristics and calcium level in the domestic duck.

Adult laying domestic ducks (Anas platyrhynchos domesticus) were forced fed lindane (gamma-hexachlorocyclohexane) 20 mg/kg body weight daily, thrice/week and twice/week for 8 weeks. Significant shell thinning (18-21%) was observed in ducks with daily and thrice/week lindane feeding. SEM studies of thinned eggshells revealed reduced and tightly clustered mammillae with apparent decrease in intermammillary spaces and signs of inhibition of calcite formation. Such structural changes of thinned shells were associated with a significant reduction in the level of calcium both of the plasma and of shell gland of the ducks. Simultaneously, density of the pore in the shell and pore area/cm2 of the shell in these birds were drastically reduced, presumably because of total absence of 'large' pores in such shells. Such porosity change is suggestive of reduced conductivity of eggshell implying impaired hatching success. Diethyl stilboestrol post-treatment neutralized all the adverse effects of lindane on duck eggshell, indicating induced estrogen deficiency in such birds by lindane.

Animals↗
PubMed1986

Flow in arteries in the presence of stenosis.

Of concern in the paper is a study of blood flow in an arterial segment having a stenosis. The artery is modelled as an initially stressed orthotropic elastic tube filled with a viscous incompressible fluid. The analysis is based on the assumption of the presence of a mild stenosis in the artery. Blood is treated as a Newtonian fluid. The effect of the surrounding connective tissues on the motion of the wall has been incorporated. Propagation of small amplitude harmonic waves, generated due to the flow of blood where the wave length is large compared to the radius of the arterial segment, is is considered in detail.

Arterial Occlusive Diseases↗
PubMed1986

Effect of lindane on clutch size and level of egg yolk protein in domestic duck.

Lindane (gamma-hexachlorocyclohexane) was administered to laying ducks (Anas platyrhynchos domesticus) in 3 doses viz. (1) 20 mg/kg body weight daily, (2) 20 mg/kg body weight thrice weekly and (3) 20 mg/kg body weight twice weekly for 8 weeks. Egg laying was immediately stopped for 3 weeks in the first 2 groups and when resumed it became highly irregular with clutch size drastically reduced (1 against 7 of control ducks). The initial delay was absent in the 3rd group and reduction in clutch size was also marginal (5 against 7). Laying frequencies were 8.3%, 11.7% and 40% in Groups 1, 2 and 3 birds respectively against 50% frequency of the normal ducks. Hepatic, plasma and ovarian vitellogenin levels were substantially reduced in the first 2 groups. At the same time liver RNA level was markedly reduced. Ovary of such birds lack mature vitellogenic follicles and the thecal layer of moderately differentiated oocytes became highly atrophic. Stilbestrol (50 mg/kg body wt--single injection) administration to lindane fed pauci-layer ducks restored egg laying within 24 h, with return of a normal level of plasma vitellogenin and hepatic RNA. The results suggest that lindane induced estradiol insufficiency causes inhibition of hepatic RNA and yolk protein synthesis, thereby preventing transformation of moderately differentiated oocytes to mature vitellogenic follicles, delaying ovulation and thus drastically reducing clutch size.

Administration, Oral↗
PubMed1985

Effect of lindane on cytology and cytochemistry of exfoliated vaginal cells.

Intraperitoneal injection of 5 mg or 10 mg per kg body weight of technical grade lindane twice weekly in Charles-Foster female rats induced marked disturbance of the estrous cycle, prolonging the proestrus phase considerably (5-7 times more compared to the normal) and thereby delaying ovulation. Exfoliated cells at proestrus are marked by high concentrations of glycogen, SDH and alkaline phosphatase while estrus is characterized by increased activity of acid phosphatase and mucopolysaccharides. Corresponding changes in the polysaccharides concentrations and enzyme activities of the exfoliated cells seen in the lindane treated rats were well correlated with disturbances of the cycle. The data suggest that lindane exerts an estrogen-like effect by inducing a temporary negative feedback on pituitary gonadotropin secretion.

Acid Phosphatase↗
PubMed1984

A study of rotational brain injury.

Of concern in the paper is an investigation on brain injuries which may occur owing to an input angular acceleration of the head. The study is based on the use of an improved mathematical model for the cranium. The eccentricity of the braincase is incorporated through the consideration of a prolate spheroidal shell as the representative of the skull. Also the dissipative mechanical behaviour of the brain material (as per the observations of experimenters) has been accounted for by considering the material contained in the shell as viscoelastic. The problem is formulated in terms of prolate spheroidal coordinates. The singularities of the governing equations of motion (when expressed in the prolate coordinate system) are removed by a suitable transformation of the concerned dependent variable, viz. the one that stands for the angular displacement of a representative point of the system. In the first place the solution of the boundary value problem is sought in the Laplace transform space, by employing a finite difference technique. Use of the alternating-direction-implicit method together with Thomas algorithm was made for obtaining the angular acceleration in the transformed space. The Laplace inversion is also carried out with the help of numerical procedures (Gauss quadrature formula is used for this purpose). The results of the parametric study are presented through graphs. The plots illustrate the shear stresses and strains in the brain medium. A meaningful comparison of the computational results with those of previous investigations indicate that the eccentricity of the braincase plays a significant role in causing injury to the brain.

Animals↗
PubMed1982

A free-vibration analysis for the human cranial system.

The problem of free-vibration of the cranial vault is studied in the paper by taking into account the dissipative material behaviour of both the skull and the brain. Two mathematical models are considered for this purpose. In one model, the layered structure (inner table, diploë and outer table) of the skull is considered, the outer surface of the skull being assumed to be traction-free while the second model assumes the homogeneity of the skull but takes into account the mechanical influence of the scalp. Results of numerical computation show that the dissipative material behaviour of the skull as well as the brain and also the mechanical influence of the scalp have a significant effect on the frequency spectrum of the freely vibrating cranial system.

Brain↗