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Biomedical subjects

V N Reddy

Publications and source records attributed to V N Reddy.

At least 91 records · Page 5Linked to original sources
PubMed1984

In vivo observation of lens protein diffusivity in normal and X-irradiated rabbit lenses.

Using the techniques of quasielastic light scattering spectroscopy we have studied in vivo the effect of X-irradiation on the diffusivity of lens proteins as a function of position in the lens and time after irradiation. The findings were compared with those for normal lenses in vivo. The experimentally observed correlation functions show marked changes in the protein diffusivity well before substantial biochemical changes take place.

Animals↗
PubMed1984

A direct correlation between the levels of ascorbic acid and H2O2 in aqueous humor.

There is evidence that H2O2 present in aqueous humor arises from ascorbic acid which is also present in this fluid, but the extent to which peroxide is derived from ascorbic acid is not known. We have measured the concentrations of H2O2 and ascorbic acid normally present in the aqueous humor of various species and also under conditions in which the level of ascorbic acid in the fluid was experimentally altered. In aqueous humor of rabbit and guinea pig the concentration of ascorbic acid was 10 times higher than that present in aqueous of rat and frog. Similarly, the concentration of H2O2 was four to 10 times higher in rabbit and guinea pig aqueous compared to that in rat and frog. Consistent with the higher concentration of ascorbic acid in posterior compared to anterior aqueous humor in the rabbit, the concentration of H2O2 was also significantly higher in the posterior aqueous. When ascorbic acid in rabbit aqueous humor was elevated by intraperitoneal administration of the compound, there was a significant increase in the level of H2O2 in both anterior and posterior aqueous humor. Moreover, when the level of ascorbic acid was lowered experimentally by placing guinea pigs on an ascorbic acid deficient diet, a 10-fold decrease in the level of both ascorbic acid and H2O2 was observed in the aqueous humor. Upon returning the animals to a normal diet, the concentrations of both compounds returned to control values. The direct correlation between the concentrations of ascorbic acid and H2O2 in aqueous humor suggests that ascorbic acid is the primary source of H2O2 in this fluid.

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PubMed1984

Protein synthesis in x-irradiated rabbit lens.

The present study deals with the incorporation of 35S methionine into lens crystallins as a function of time after x-irradiation. Crystallin synthesis is first affected approximately 4 weeks following x-irradiation. This coincides with the time period at which the ratio of the two cations in the lens is affected, as shown in earlier studies. A greater decrease in 35S-methionine incorporation into crystallins is observed between 5-7 weeks following x-irradiation in good agreement with a cation imbalance at these time intervals. These studies also revealed for the first time that the change in cation distribution can affect not only crystallin synthesis, but also the synthesis of certain polypeptides of lens membranes. No alteration in protein synthesis could be detected in lens epithelium even after 7 weeks following irradiation. In addition to the effect of Na+ and K+ levels on protein synthesis, an impaired transport of amino acids into the x-rayed lens was also found to be a factor in the observed reduction in synthesis of the crystallin, cytoskeletal and membrane proteins of the fiber cells. It is concluded that Na+/K+ ratio as well as the availability of amino acids in the lens are important factors in protein synthesis of x-ray cataracts.

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PubMed1983

The arterially perfused enucleated rabbit eye as a model for studying aqueous humor formation.

The rate of turnover of aqueous humor (Kout), as measured by the decay of radioactive inulin from the anterior chamber of the enucleated eye, was similar to the rate of loss of 125I-RISA (radioiodinated serum albumin) from the eye of a living rabbit. Arterial perfusion with 125I-RISA or rabbit serum showed that the permeability characteristics of the blood-aqueous barrier to protein molecules are unaffected in the enucleated eye. The viability of the enucleated eye for secretion of ascorbic acid was also examined, but the results were inconclusive.

Animals↗
PubMed1983

Scanning electron microscopy of X-ray-induced cataract in mice on normal and galactose diet.

The possible multiple effect of galactose diet and X-irradiation on cataract development in mice was investigated by scanning electron microscopy. X-ray cataracts were induced by maintaining animals either on a normal or 50% galactose diet. No detectable changes in lens morphology were seen in animals fed galactose alone compared with normal controls. 2 months after X-ray, less damage had occurred to the lenses of the galactose-fed animals compared to those on a normal diet. At 4 months after X-ray, animals on a normal diet developed mature cataracts, while in the galactose-fed animals they were delayed by 0.5-1.5 months. Suppression of the development of X-ray cataract by galactose feeding may be related to the ability of this sugar, which accumulates in mouse lens due to the low levels of aldose reductase, to act as a free radical scavenger.

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PubMed1983

Changes in the distribution of lens calcium during development of x-ray cataract.

The present study was designed to examine the possible role of calcium in the opacification of x-ray-induced cataract in rabbit. The results demonstrate that the concentration of calcium in x-rayed lenses, just prior to lens hydration (7.5 weeks postirradiation), was twice that present in contralateral control lenses. At this stage of immature cataract, the lens nucleus remained transparent and maintained a normal level of calcium, but the lens cortex, containing regions of subcapsular opacification, accumulated a level of calcium that was twice that of the control. In the completely opaque mature cataract, (8-9 weeks postx-ray), both the cortex and nucleus had gained significant amounts of calcium. As the concentration of total calcium increased in the immature x-ray cataract, the amount of the cation bound to membranes and insoluble proteins of the cytosol also increased comparably. However, the relative proportion of calcium in the various fractions remained unaltered in the immature cataract; in both control lenses and immature cataracts, 20% of the total calcium remained in the membrane pellet and 70% was located in the soluble protein fraction. Only in the mature stage of cataract was a shift in the distribution of calcium apparent, as the proportion of calcium in the soluble protein fraction increased to 90%. Although only 7% of the total calcium in a mature cataract was bound to membrane, the amount represented a fivefold increase over the control. The results of this study demonstrate that an elevation in lens calcium accompanies the opacification process in x-ray cataract. The work also suggests that changes in calcium levels are not likely to result from inactivation of Ca-ATPase.

Animals↗
PubMed1983

Lens membrane damage associated with cryoextraction.

The effects of cryoextraction on transport characteristics of rabbit lenses were evaluated by measuring Na+ and Ca++ levels, initial rates of 86Rb accumulation, and bioelectric potentials. The results demonstrate that membrane damage results from cryoextraction and is partially reversible during subsequent culture. While the decline in potential often exceeds 30 mV, maximum recovery of 80% occurs during a 1-hour incubation in TC199 at 37 C. Changes in the integrity of the membranes also are indicated by the finding that rates of 86Rb accumulation in cryoextracted lenses are approximately 44% less than the rates found in control lenses after a 20-hour culture in TC199. The degree of damage incurred by lens membranes also is reflected by a 10% increase in Na+ and 20% increase in Ca++ levels during 3 hours of culture. After extended culture periods, further increases in the concentration of Na+ (40%) and Ca++ (120%) were found to occur. Brief exposure of cryoextracted rabbit lenses to physiologic saline in a manner similar to that employed for photographic documentation of cataracts resulted in a marked decline in potential, 86Rb uptake, and an increase in Na and Ca content. In contrast, saline had little or no effect on these parameters in lenses excised by cutting the zonules. The results suggest that the observed decline in 86Rb accumulation in a limited number of cryoextracted cortico-nuclear cataracts compared with clear eye bank lenses may be attributed, in part, to damage to lens membranes by cryoextraction.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1983

Membrane glycoproteins of Philly mouse lens.

The Philly mouse is a new model for genetic cataracts, in which there is an apparent defect in lens membrane permeability. This abnormality results in electrolyte imbalance and lens hydration, typical of an osmotic cataract. Since membrane glycoproteins are believed to be involved in transport processes, we have studied the changes in these polypeptides in the Philly mouse lens during cataract development and compared them with those in the control Swiss-Webster mouse. The membrane glycoproteins were labeled by treatment with galactose oxidase and tritiated borohydride. Radioactivity was found to be incorporated into six glycoproteins of approximate molecular weights of 128 k, 103 k, 82 k, 71 k, 35 k, and 22 k daltons. The 35 k polypeptide is the major glycoprotein in the mouse lens membrane and shows increased incorporation of the tritium label with progression of the cataract. In contrast to the murine lens, the 35 k peptide could not be detected in rabbit lens membranes. Other changes observed in glycoproteins of the Philly mouse lens during cataract development were a loss of the 103 k and 71 k polypeptides and a corresponding increase in the 66 k polypeptide. These changes in glycoproteins may be related to the permeability changes and cataract development in the Philly mouse lens.

Animals↗
PubMed1982

The effect of X-irradiation on Na-K ATPase and cation distribution in rabbit lens.

The Na-K ATPase activity of rabbit lens was measured at various times after exposure to a single dose of 2000 rads of X-ray and was compared with that in contralateral control eyes. A decrease in enzyme activity in both whole lens and in isolated capsule-epithelium was first observed 3 to 4 weeks after irradiation and became increasingly marked at 7.5 weeks after X-ray. These findings are consistent with our earlier observations that active transport of cations is reduced in these lenses and support the view that loss of membrane ATPase is responsible for the impairment of the cation pump in X-irradiated lenses. Despite a significant loss of the enzyme, X-irradiated lenses were able to maintain near normal levels of total cations (Na+ + K+), thus accounting for their normal hydration. The results of the changes in lens Na+ and K+ levels revealed that between 4 and 7.5 weeks after X-ray, the gain in Na+ was compensated by an equivalent loss of K+. A breakdown of this relationship of 1:1 exchange of Na+ for K+ is accompanied by a disproportionate increase in Na+ and water.

Animals↗
PubMed1982

Phase separation of X-irradiated lenses of rabbit.

The phase separation temperature (Tcat) was studied as a function of time (age) after the administration of a single dose of radiation (2000 rad), which induces cataract in the rabbit lens. In the normal unirradiated lens, Tcat decreases linearly with age at a rate (DTcat/dt) approximately 2.2 degrees/week. In the irradiated lens, Tcat initially decreases with age much less than the normal lens, then rises sharply with age at the time of the appearance of opacity in the living rabbit eye. We suggest that the phase separation temperature may serve as a sensitive and early indicator of cataractogenic processes in the lens.

Animals↗
PubMed1982

Ca++-induced cataract.

Cataracts in cultured rabbit lenses were produced by elevation of internal calcium. Experimental procedures were successful in increasing levels of total and bound Ca++, often without significant changes in sodium, potassium, or water content. Although the excess in calcium was predominantly associated with water-soluble proteins and was freely diffusible, a significant amount was bound to membranes and cytosol water-insoluble proteins. Thus, in lenses with a 10-fold increase in total Ca++, the bound Ca++ increased twofold, nearly 35% of which remained fixed to water-insoluble and membrane proteins after exhaustive (72 hr) dialysis. In contrast, over 95% of the Ca++ in water-soluble protein fractions was removed by dialysis.

Animals↗
PubMed1982

The role of glutathione metabolism in the detoxification of H2O2 in rabbit lens.

Aqueous humor is known to contain a significant level of H2O2, but the mechanisms by which ocular tissues protect against oxidative damage are not well understood. With the use of C-1-, C-2-, and C-6-labeled glucose, the contribution of glutathione (GSH) metabolism and the hexose monophosphate shunt (HMS) to the detoxification of peroxide in the lens has been evaluated. It was observed that H2O2 in the culture medium disappeared rapidly (0.5 mumol H2O2/lens/hr) upon incubation of a rabbit lens at 37 degrees C. At 0 degrees to 3 degrees C, however, the rate of disappearance of H2O2 was only one fifth of that observed at the higher temperature. In the absence of a lens or after pretreatment of the lens with methyl mercuric hydroxide, the rate of disappearance of peroxide from the medium was reduced to nearly zero. When a nearly constant level of H2O2 (0.05 to 0.07 mM) was maintained in the medium by means of a peristaltic pump, the amount of CO2 liberated by the HMS at 37 degrees C was found to be three times that liberated from lenses cultured in the absence of peroxide. No change was noted in the level of GSH in the H2O2-treated lenses at 37 degrees C. A significant decrease in GSH was observed, however, at 0 degrees to 3 degrees C, suggesting nonenzymatic oxidation of the tripeptide at the lower temperature. The results indicate that GSH metabolism and the HMS pathway contribute significantly to the detoxification of H2O2 in the lens.

Animals↗
PubMed1981

Metabolic studies on calcium transport in mammalian lens.

Three important findings concerning the calcium pump in a mammalian lens are reported: 1) glycolysis is sufficient to support active transport of calcium in the young rabbit lens; 2) in addition to the epithelium posterior and anterior fibers are involved in calcium transport; 3) inhibition of glycolysis and the calcium pump result in calcium accumulation and subsequent opacification. That respiration does not contribute to the energy needs of the Ca++ pump is based on results which demonstrate that cyanide, dinitrophenol, and azide have no effect on 45Ca efflux when glucose is present. Moreover, incubation of lenses for 20 hrs. in the presence of cyanide fails to alter the internal concentration of calcium. The inhibition of glucose metabolism with iodoacetate (IAA) results in the accumulation of calcium to a level of 0.71mM and the formation of superficial subcapsular opacities. Evidence that fibers are also responsible for calcium extrusion consists of two findings: 1) removal of the epithelium from a lens results in calcium accumulation but the addition of IAA to such a lens results in a further gain in calcium; 2) the accumulation of 45Ca across the posterior surface of a lens partially immersed in medium is accelerated following inhibition of glycolysis.

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