Fishes show three types of senescence. Lampreys, eels and pacific salmon exhibit rapid senescence and sudden death at first spawning. The guppy, red panchax, medaka, platyfish, Indian murrel and many other teleosts undergo gradual senescence, as observed in most of the vertebrates. A number of fishes (e.g. sturgeons, paddlefish, female plaice, flatfish, rock-fish) show indeterminate growth, the occurrence of senescence in them is supposed to be very slow or negligible. Neuroendo-crine mechanisms are involved in rapid senescence. Most of the evidences in favour of the occurrence of senescence in fishes have been derived from studies in species showing gradual senescence. Age-related increases in mortality rate, accumulation of lipofuscin, lipid peroxidation, collagen cross-linking and decreases in growth rate, reproductive capacity and protein utilisation are clearly marked in such species. Anatomical changes in various organs during ageing also confirm increases in degenerative changes and pathological symptoms. Dietary restriction and lower environmental temperature retard the ageing processes in a few species showing gradual senescence. These results tentatively support the contention of commonality in mechanism of ageing processes in vertebrates. At present, anatomical, cellular, biochemical and genetic evidences in support or against the occurrence of slow senescence or negligible senescence in long-lived fish species are almost nonexistent. Extensive studies on ageing in fishes are needed to explain the multiple mechanisms which are not unexpected considering the number and variety of the existing species.
Like in fishes, the reptiles appear to show three types of senescence. The African skink, Mabuya buettneri, shows rapid senescence similar to death at mating observed in Salmon and marsupial mouse. Most of the lizards and snakes undergo gradual senescence comparable to the pattern exhibited by a majority of vertebrates. On the other hand, turtles, tortoises and crocodiles continue to grow throughout life and are thus credited with slow or negligible senescence. Evidences and mechanisms of rapid or negligible senescence in reptiles are still fragmentary and unclear. Findings in a few species of lizards (Calotes versicolor) and snakes (Natrix natrix) showing gradual senescence support the concept of commonalities in ageing phenomena in vertebrates. An age-related increase in the stability of collagen and accumulation of altered enzyme molecules, a decrease in metabolism and response to stress-enhanced anti-oxidative defence mechanisms and the nature of responses to hormones, restricted diet and lower environmental temperature corroborate the concept. On the other hand neither the increase in mortality rate and accumulation of lipofuscin nor the reproductive senility have been shown conclusively in ageing reptile populations. It is likely that there are multiple mechanisms of senescence in reptiles. Further studies on selected species from among the 6,000 living species are necessary to unravel the phenomena.
Background: Although aluminium (Al) has been implicated in various neuropathological states with aging due to its involvement in neurotoxicity, the exact role of the metal ion is still unclear. Objective: The aim of the present study is to ascertain whether the antioxidant enzymes of the brain protecting from oxidative damages which accumulate with aging are regulated by Al in an age-dependent manner. Method: The inhibitory effect of Al on the catalase activity of brain homogenates of two species of poikilothermic vertebrates was studied in vitro using a spectrophotometric method. Results: At a final concentration of 666 µM, the metal ion inhibited the enzyme activity of the brain in both species. In fish brain the degree of inhibition was not age-dependent. On the other hand, the rate of inhibition increased between young and middle-aged lizards followed by a decline in the old counterparts. Conclusion: Al inhibits catalase activity but this effect may not be a major contributing factor in the aging of the brain in the two species capable of maintaining their antioxidant capacity until old age.
I . Long-term clinical and biochemical vitamin C (ascorbic acid and dehydroascorbic acid) status and dietary intake of vitamin C were monitored for 18 months in twenty-three relatively-healthy elderly subjects living at home in the north of England.2. Plasma vitamin C showed a strong positive correlation with buffy-coat vitamin C both cross-sectionally between subjects and longitudinally within subjects; plasma levels, therefore, were almost as good an index of Iong-term status as buffy-coat levels.3. Vitamin C intake was strongly correlated with plasma and with buffy-coat levels both between subjects and within subjects. This contrasts with the poor correlation observed between riboflavin intake and biochemical riboflavin status in the same subjects.4. Subjects with relatively high average intakes showed considerable seasonal variation, and several widely-spaced measurements would be needed to characterize their long-term status accurately. Those with low average intakes and blood levels showed little variation during the study.5. The strongest within-subject correlation was obtained by relating the biochemical values to the 7 d dietary intake directly preceding the biochemical analysis. Blood and tissue levels therefore appear to be strongly related to the current dietary intake.6. Although some subjects had blood vitamin C levels consistently within the region associated with biochemical deficiency, none showed clinical evidence of specific deficiency symptoms.7. After the main study, fifteen of the subjects received supplementary vitamin C for z months. Plasma and buffy-coat levels rose sharply, but fell to presupplementation levels within I month of withdrawal, emphasizing the transitory nature of increased tissue levels. No significant changes were detected in the following collagen-related urinary ratios : hydroxyproline : creatinine, proline : creatinine, proline : total amino-nitrogen and proline: hydroxyproline in hydrolysates either of whole urine or of various fractions. These variables thus appear to be insensitive to short-term changes in vitamin C status over the ranges encountered in this study.
In roots all lipids were increased. A number of lipid substances in the total extractable materials were measured. 3. Protein concentration was decreased in treated plants and carbohydrate fraction concentrations were increased reciprocally. 4. The esterified sterols of the shoots exhibited fast-reacting characteristics to the Liebermann-Burchard reagent.
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