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N Lake

Publications and source records attributed to N Lake.

At least 37 records · Page 2Linked to original sources
PubMed1989

Effects of dark maintenance on retinal biochemistry and function during taurine depletion in the adult rat.

Light dependence of the effects of taurine depletion on retinal function and biochemistry was examined in albino rats housed either in cyclic lighting or in continuous darkness. Measurements of retinal taurine, DNA, and rhodopsin contents, and electroretinogram amplitudes were made at weekly intervals. Naka-Rushton parameters were estimated for the b wave amplitude-intensity function. No significant effects of lighting regime were observed on retinal taurine levels in untreated rats, or on the time course or extent of taurine depletion in animals treated with guanidinoethyl sulfonate, an antagonist of taurine transport. In both lighting schemes, treatment led to a linear reduction of retinal taurine content which plateaued after 5-6 weeks at 50% of control despite continued treatment. DNA values did not differ among groups, whereas rhodopsin levels doubled in both groups of dark-maintained rats. For treated rats housed in cyclic lighting, the onset of electroretinogram deficits paralleled the loss of retinal taurine in the absence of changes in rhodopsin levels or cell death. Vmax was significantly reduced after 4 weeks of treatment. In contrast, for rats housed in continuous darkness, there were no significant differences in electroretinogram parameters between control and taurine-depleted rats until after 10-14 weeks of treatment. This implies that light exposure accelerates the appearance of functional changes associated with retinal taurine deficiency. The basis of the light dependence and the interpretation of related studies is discussed.

Animals↗
PubMed1989

Immunocytochemical localization of taurine in the mammalian retina.

This paper describes the first demonstration of taurine-like immunoreactivity in the mammalian retina using an antiserum raised in rabbits. In rat, cat and guinea pig retina a peroxidase-antiperoxidase immunocytochemical technique showed high levels of taurine immunostaining in photoreceptor inner segments and synaptic terminals, in subpopulations of amacrine and bipolar somata and their synaptic processes in the inner plexiform layer, including numerous large terminals near and on ganglion cell somata. Using the Protein A-gold technique for ultrastructural studies in the rat, the presence of synaptic ribbons confirmed that some of these taurine-containing terminals were from bipolar cells. Lower levels of immunostaining were seen in the pigment epithelium and distal parts of glial cells.

Animals↗
PubMed1988

Effects of beta-alanine treatment on the taurine and DNA content of the rat heart and retina.

Experimental evidence has suggested that the high endogenous levels of taurine found in the rat heart and retina are maintained to a large extent by transport processes out of the blood, rather than by endogenous biosynthesis. When these high levels are depleted, dysfunction ensues. In vitro studies have shown that beta-alanine is a good antagonist of these transport processes. The current studies were done to evaluate the feasibility of depleting heart and retinal taurine levels in vivo through treatment of adult rats either orally or with injections of beta-alanine. None of the treatments had significant effects on retinal taurine content; ventricular taurine was reduced in some situations, but the effects were not maintained, nor as large as with another transport antagonist. No functional changes were observed. Oral treatment with beta-alanine had fewer obvious side effects than injections, but all treated rats had body weights less than age-matched controls.

Administration, Oral↗
PubMed1988

Taurine depletion leads to loss of rat optic nerve axons.

The number of axons in the optic nerve have been examined in rat pups raised by control or taurine-depleted mothers, at 21, 28 and 40 days after birth. Optic nerves from the mother rats were also studied. Taurine depletion of dams and some litters after weaning was achieved by in vivo treatment with guanidinoethyl sulfonate, an inhibitor of taurine transport. Retinal taurine content was reduced by this procedure and reductions in axon density (axons per area) were found in some groups. Comparison of axon densities obtained from light or electron micrographs suggested that taurine-deficient pups might have a higher proportion of small diameter fibres than controls, perhaps due to slowed growth and/or myelination. Reductions in the calculated total number of optic nerve fibres attained statistical significance consistently only in the treated dams. Ganglion cell degeneration may be direct or secondary to effects on taurine-sensitive elements at more distal retinal sites.

Animals↗
PubMed1987

Effects of taurine depletion on rat cardiac electrophysiology: in vivo and in vitro studies.

Electrocardiograms were monitored in unanesthetized rats during treatment with drinking water containing guanidinoethyl sulfonate (GES), an inhibitor of taurine transport, which depleted cardiac taurine content. Treatment led to a selective prolongation of the QT interval which was highly correlated with the degree of taurine depletion (r2 = 0.92, p less than .001). Compared to controls, the duration of ventricular muscle action potentials was significantly increased in GES-treated rats, and this accounted for the prolongation of QT intervals. Oral taurine supplements reversed GES-induced cardiac taurine depletion and the associated increased duration of action potentials and QT intervals. In vitro superfusion with 0.2-10 mM GES or taurine had no effect on action potentials of control or GES-treated rats. These data indicate that intracellular taurine may play a role in regulating myocardial action potential duration, particularly during repolarization.

Action Potentials↗
PubMed1987

Electroretinographic alterations and their reversal in rats treated with guanidinoethyl sulfonate, a taurine depletor.

Studies in man and other vertebrates have shown an association between taurine deficiency and retinal dysfunction. The electrophysiological consequences of treating rats with the taurine depletor, guanidinoethyl sulfonate, were assessed from electroretinograms to a range of intensities. Analysis of the Naka-Rushton parameters for the scotopic b-wave amplitude-intensity relationship showed that 4 weeks of treatment led to a significant reduction in Vmax, with no changes in sigma or n. The a-wave amplitude was similarly affected so that the b/a ratio was unchanged by treatment. Responses from GES-treated animals also had increased latencies to b-wave peak compared to control. Responses from treated rats could be matched for amplitude by selecting control responses evoked by lower intensities. The latencies of these amplitude-matched responses did not differ, suggesting that the inherent relationship between latency and amplitude was not changed by treatment, and that the prolonged latencies of the responses from treated rats were appropriate for their reduced amplitude. Thus with respect to latency and amplitude, the electroretinogram b-wave responses of guanidinoethyl-sulfonate-treated animals resembled those of untreated rats to lower intensities of light. Our interpretation is that treatment led to a reduction in the efficacy of photoreceptor transduction which produced secondary alterations in the b-wave. Termination of treatment after 4 weeks was followed by partial or complete recovery when tested 55 days later.

Animals↗
PubMed1987

Retinal morphology in rats treated with a taurine transport antagonist.

Previous studies have shown that chronic treatment of rats with guanidinoethyl sulfonate (GES), an antagonist of taurine uptake, leads to depletion of retinal taurine content and electroretinogram abnormalities. In this study we examined with the light- and electron microscope the retina and pigment epithelium of mother rats treated for 8 weeks with 1% GES in their drinking water. Pigment epithelial cells appeared swollen, sometimes with mitochondrial vacuolization and loss of cytoplasmic density, and changes in nuclear shape and chromatin distribution. Photoreceptor cells had shorter outer segments with disarray of disks, swollen inner segments and nuclei, and loss of synaptic terminal contents. These degenerative changes frequently led to cell death, indicated by loss of photoreceptor cell nuclei and shrinkage of the outer nuclear layer, and disappearance of photoreceptor synaptic terminals from the outer plexiform layer. Narrowing of the outer plexiform layer was due also to the retraction of cell processes from higher-order neurons. Quantitative studies of the retina along the vertical meridian passing through the optic nerve head showed that treatment resulted in significant reductions in the number of rod-cell nuclei per field, the width of the outer nuclear layer, and the width of the inner retina. Effects were more pronounced in the superior than the inferior hemisphere, reminiscent of findings in light-damage studies. A possible role for taurine in the cellular defence mechanisms against light- and oxygen-induced damage is suggested.

Animals↗
PubMed1983

In vitro studies of guanidinoethyl sulfonate and taurine transport in the rat retina.

The present study reports inhibition of taurine uptake in the rat retina in vitro to 49% of control by 1 mM guanidinoethyl sulfonate. No efflux of preloaded [14C]taurine was observed by incubation in the presence of guanidinoethyl sulfonate. The in vivo depletion of retinal taurine by guanidinoethyl sulfonate treatment may arise owing to antagonism of taurine transport into the retina from the blood.

Animals↗
PubMed1983

Taurine depletion of lactating rats: effects of developing pups.

Taurine is in high concentration in the milk of most mammals. Intraperitoneal injection of [35S]taurine into lactating rats leads to the appearance of label in the milk, and the dpm/ml milk are significantly decreased by treatment with guanidinoethyl sulfonate (GES), an analog of taurine. Pups nursed by GES-treated mothers have retinal taurine levels about 45% lower than controls during the period from birth to 17 days old suggesting a dependence of retinal taurine on dietary intake during the neonatal period. These deficits in taurine may be associated with visual dysfunction as seen in adult rats depleted of retinal taurine.

Aging↗
PubMed1982

Depletion of taurine in the adult rat retina.

Taurine is the major free amino acid of the vertebrate retina. Treatment of rats with guanidinoethyl sulfonate (GES), a taurine analogue which competes with taurine for transport sites, leads to depletion of 60% of retinal taurine with little effect on other free amino acids. Supplementation of the diet with 0.3% taurine gives partial protection against depletion, confirming that taurine-GES competition underlies part of the effects. The magnitude of the depletion suggests the importance of taurine transport across the blood-retinal barrier for the maintenance of retinal taurine levels.

Amino Acids↗