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Biomedical subjects

A Sreenivasan

Publications and source records attributed to A Sreenivasan.

At least 37 records · Page 2Linked to original sources
PubMed1976

Further characterization of rat liver mitochondrial fractions. Lipid composition and synthesis, and protein profiles.

1. Heavy and light mitochondrial fractions obtained by differential centrifugation were further characterized with respect to their lipid composition and synthesis and protein profiles, as seen by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. 2. The light mitochondrial fraction was rich in total lipids, phospholipids and cholesterol. The cardiolipin content, however, was low. 3. Rates of [3H]glycerol incorporation into phospholipids of heavy mitochondria and microsomal fractions were almost identical. On the other hand, incorporation into the individual phospholipids in light mitochondria was about 4-6 times higher. Incorporation into cardiolipin of light mitochondria was about 10-fold higher than in the heavy mitochondria. 4. Analysis of protein profiles by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis showed that the pattern obtained for the light mitochondria was similar to that for heavy mitochondria. However, the light fraction was relatively poor in high-molecular-weight proteins and rich in low-molecular-weight proteins. The microsomal protein profile was altogether different. 5. The significance of these findings is discussed in relation to mitochondrial biogenesis.

Animals↗
PubMed1976

Action of hydrocortisone at a translational level in the rat liver.

Administration of hydrocortisone to adrenalectomised rats elevated levels of both free and membrane-bound polysomes in liver and led to marked shifts in their sedimentation profiles in favour of heavier polysomes. The rate of nascent polypeptide formation was also found to be enhanced in response to the hormone but this effect was mainly confined to the site of free polysomes. These results suggest that besides its well-known potentiating action at the transcription level, the hormone elicits selective stimulatory response at the translation level.

Adrenalectomy↗
PubMed1976

Mechanisms underlying decreased protein and RNA synthesis in the rat spleen following whole-body X-irradiation.

Whole-body exposure of rats to 1000 R X-rays resulted in decreased rates in protein and RNA syntheses in the spleen from the fourth post-irradiation hour. These changes correspond well with impaired ability of nuclei to polymerise RNA, reduction in template efficiency of chromatin, decrease in the activity of RNA polymerase and inhibition in histone phosphorylation. Protection of the spleen by lead shielding during whole-body exposure to X-rays largely eliminated the observed alterations in protein and nucleic acid synthetic machineries. This suggests that the radiation-induced inhibition in protein and RNA syntheses is mainly due to the direct action of radiation on the spleen itself.

Animals↗
PubMed1975

Regulation of mitochondrial protein turnover by thyroid hormone(s).

1. The effect of thyroidectomy on turnover rates of liver, kidney and brain mitochondrial proteins was examined. 2. In the euthyroid state, liver and kidney mitochondria show a synchronous turnover with all protein components showing more or less identical half-lives compared with the whole mitochondria. The brain mitochondrial proteins show asynchronous turnover, the soluble proteins having shorter half-lives. 3. Mitochondrial DNA (m-DNA) of liver and kidney has half-lives comparable with that of whole mitochondria from these tissues. 4. Thyroidectomy results in increased half-lives of liver and kidney mitochondria, with no apparent change in the half-life of brain mitochondria. 5. A detailed investigation of the turnover rates of several protein components revealed a significant decrease in the turnover rates of mitochondrial insoluble proteins from the three tissues under study. 6. The turnover rates of m-DNA of liver and kidney show a parallel decrease. 7. Thus it is apparent that thyroid hormone(s) may have a regulatory role in maintaining the synchrony of turnover of liver and kidney mitochondria in the euthyroid state. Turnover of brain mitochondria may perhaps be regulated by some other factor(s) in addition to thyroid hormone(s). 8. It seems likely that during mitochondrial turnover m-DNA and insoluble proteins may constitute a major unit. 9. The mitochondrial protein contents of the three tissues are not affected by thyroidectomy. 10. No correlation was seen between the turnover rate of mitochondria and cathepsin activity in any of the tissues under study in normal or thyroidectomized animals. 11. On the other hand, mitochondrial proteinase activity shows good correlation with the turnover rates of mitochondria in normal animals, and a parallel decrease in activity comparable with the decreased rates of turnover is observed after thyroidectomy. 12. It is concluded that mitochondrial proteinase activity may play a significant role in their protein turnover.

Animals↗
PubMed1975

Effect of whole-body irradiation on transcription in the rat thymus.

Studies were carried out to elucidate the mechanism underlying the impairment in RNA synthesis in the rat thymus after whole-body exposure to X-rays (1000 rad). The ability of thymus nuclei to catalyse RNA polymerization in vitro was adversely affected in irradiated rats. Further experiments showed that whole-body irradiation caused a considerable decrease in both the activity of RNA polymerase and the template efficiency of chromatin but not in that of DNA isolated from chromatin. These radiation-induced changes in transcription seem to arise partly from the direct effect of radiation on the thymus itself and partly from the abscopal mechanism(s).

Animals↗
PubMed1975

Effect of X-irradiation on vitamin B12 binding capacity to intrinsic factor.

The effects of whole-body X-irradiation on vitamin B12-protein complex formation in gastric juice after oral administration of [57Co]-B12 have been studied. Two proteins with B12-binding activity have been isolated by gel filtration from gastric juice. 57Co-activity, recovered from B12-protein complex in gastric juice, is found to be about 30% less in the X-irradiated rat. In serum, vitamin B12 is mainly associated with alpha1-globulin. Radioactivity distribution in serum globulins after intraperitoneal injection of [57Co]-B12 was similar in control and X-irradiated rats.

Animals↗
PubMed1975

Distribution of lactic dehydrogenase in X-irradiated tissues.

Exposure to whole-body X-irradiation in rats causes a marked increase in total lactic dehydrogenase (LDH) activity and decrease in H-LDH/M-LDH ratio in serum and tissues, the maximum effect being observed on the 8th post-irradiation day. While there is an elevation of M-LDH isoenzyme, H-LDH remains relatively constant. Studies on incorporation of DL-leucine-l-14C into heart LDH isoenzymes also revealed increased biosynthesis of M-LDH isoenzyme. This indicates that an adaptive mechanism is operative in the X-irradiated rats, whereby, in order to augment anaerobic glycolysis, synthesis of M-LDH is stimulated. Administration of the radioprotector cystamine does not alter the effects of X-irradiation on serum LDH activity.

Animals↗
PubMed1975

Vitamin B12 absorption in x-irradiated rats.

The effect of whole-body exposure of rats to a sub-lethal dose (400 rad) of x-rays on the absorptive capacity of intestinal mucosal cells for vitamin B12 has been studied. The rate of absorption of vitamin B12 from the intestinal loops is decreased in x-irradiated rat. Inclusion of gastric juice from normal rat does not improve the rate. A severe interference in the absorption and retention of orally fed (57-Co)-B12, as evidenced by low serum levels, decreased organ uptake and increased excretion, is observed. However, when the vitamin is administered intraperitoneally, its uptake by organs is not affected in the irradiated animal. This suggests that the observed morphological degeneration of mucosal cells in x-irradiated rats is the main reason for the malabsorption of vitamin B12. Atrophy of intestinal cells in the protein-fasted rat accentuates the adverse effects of radiation. A sharp drop in viable intestinal flora is observed within 24 h post-irradiation, but there is an increase after 3 days.

Animals↗