The Effect of Posthypoxic Hypothermia for LactateDehydrogenase Activity in Brain Cortex and BloodSerum of 14-days-old Rats

Overview

Objective:
The effect of various degree of hypobaric hypoxia and consequent hypothermia onlactate dehydrogenase (E.C.1.1.1.27) activity in blood serum and brain cortex in 14 day-old ratswas investigated.Design: Experimental study.Setting: Institute of Physiology, 1st Med. Faculty, Charles University, Prague.Methods: 14 day-old rats (Wistar of our own breed) were exposed to mild hypobaric hypoxia (correspondingto altitude of 7000 m, pO2 = 8.6 kPa, BP = 41.2 kPa, lasting 20 min) or strong hypobarichypoxia (corresponding to altitude of 9000 m, pO2 = 6.4 kPa, BP = 30.7 kPa, lasting 30 min). Just afterhypoxic stress the animals were killed by decapitation and on cooled block the grey cortical matterwas removed. Blood serum samples as well as brain cortext homogenates were immediatellyincubated in three variously tempered media (38 °C = control values, 30 °C and 22 °C = hypothermicconditions). The incubation was over (30 min.), and the lactate dehydrogenase (LDH) activity wasfollowed using the Lachema test.Results: The LDH activity was infl uenced by mild hypobaric hypoxia (7000 m) neither in bloodserum nor in brain cortex. Also the values of LDH activities registered in normo or in hypothermicconditions were not different as compared with control values. The strong hypoxia(9000 m) evokes in brain cortex homogenates simultaneously with normothermia and posthypoxichypothermia (30 °C) signifi cant increase of LDH activity. In blood serum the strong hypoxiaincreased the LDH activity; in subsequent hypothermic condition (22 °C) the LDH activity wasmore lowered.Conclusion: The LDH activity in brain cortex as well as in blood serum of young rats (Wistar)seems to be resistent to mild hypoxia (7000 m) as well to hypothermic conditions. The strong hypoxia(9000 m) evokes quite different responses: in brain cortex the LDH activities in hypothermicconditions are higher, in blood serum lower as compared with control values (14 day-oldrats stressed by hypoxia only). In control measurements the lowering temperature decreasesthe mentioned enzyme activity in brain cortex; in blood serum no signifi cant differences couldbe found.

Key words:
hypobaric hypoxia, hypothermia, lactatedehydrogenase activity, brain cortex, bloodserum