Effect of age and short-term cold stress on SDH activity and oxygen consumption of lizard brain

Effect of partial water deprivation and restricted feeding on age-related changes in two enzymes of energy metabolism in the brain of male garden lizards

The lactate dehydrogenase (LDH) activity of garden lizard brain did not change with advancing age. On the other hand the succinate dehydrogenase (SDH) activity showed a decline during maturation (young to middle-aged) remaining stabilized thereafter. Seven days of partial water deprivation did not alter the LDH activity of lizards of all three age groups but caused an increase in SDH activity of old lizards only. Restricted feeding led to a decline in the activities of both the enzymes (LDH and SDH) in young lizards and an increase in LDH activity of only the old, the response in middle-aged being insignificant. The protein content of the brain did not change during maturation, but declined in old lizards. Partial water deprivation caused an increase in protein content of the brain of both middle-aged and old lizards but not in young counterparts. Only the young lizards showed an increase in protein content of the brain in response to food restriction.

Effect of two inhibitors on succinic dehydrogenase activity in cerebral hemispheres of male garden lizards of three different age groups

Age changes in the specific activity of cerebral succinic dehydrogenase (SDH) and the effect of two inhibitors (malonate and p-chlorophenoxy acetic acid) on enzyme activity were traced in a short-lived species of reptile, Calotes versicolor, the garden lizard. The enzyme activity reached a peak level in middle-aged lizards followed by a decline in old counterparts. The enzyme inhibitions by both the inhibitors were significantly higher in old than in middle-aged and young lizards suggesting a change in specificity of SDH molecules during ageing.

Effect of cold stress and starvation on the cerebral glucose-6-phosphate dehydrogenase activity of male garden lizards of three different age groups

In the present study we observed that the cerebral glucose-6-phosphate dehydrogenase activity of male garden lizards did not change appreciably during maturation but showed a significant rise between middle-aged and old-aged groups. Whereas cold stress (1 h at 0-4 degrees C) induced a significant increase in G6PDH activity of young animals, it caused a decrease in both middle-aged and old lizards. This decrease was more severe in the old group than in the middle-aged group. Another form of stress, 72 hours of starvation, led to a significant increase in enzyme activity in young and in middle-aged lizards with young animals showing the greater effect. The old counter-parts showed a decrease in enzyme activity after starvation stress.

Age-related differences in the response of hepatic oxygen consumption to thermal stress in the male garden lizard

The main aim of the present study is to compare the thermal adaptation capacity of young, middle-aged and old lizards with respect to hepatic oxygen consumption. Cold exposure (1 h at 0-4 degrees C) caused a decline in endogenous oxygen consumption in young but did not evoke significant changes in middle-aged and old lizards. On the other hand, with 5 mM succinate the rate of respiration increased marginally only in cold-exposed old lizards. This suggests that the metabolic response to cold is age-dependent in these lizards. Exposure of homogenates at 40 +/- 1 degree C for 15 min led to a rise in the hepatic oxygen consumption of young but not in that of either middle-aged or old lizards. There were no changes in the rate of oxygen consumption upon exposure for a similar period at 45 +/- 1 degree C of liver homogenates from lizards of three different age groups. However, exposure at 51 +/- 1 degree C resulted in a higher degree of decline in the rate of hepatic oxygen consumption in middle-aged and old than in young lizards. Thus, the young lizards appear to be better-adapted to hyperthermic stress than the middle-aged and old.