Objective     To investigate effect of guanosine diphosphate (GDP) on the mitochondrial respiratory oxygen consumption and the mitochondrial membrane potential (MMP) of rat brain and explore the relationship of the change of uncoupling proteins (UCP

s

) activity with the oxygen consumption and MMP.      Methods     The mitochondria of rat brain were isolated by centrifugation. Mitochondria oxidative respiratory consu

mption was measured by Clark electrode after the treatment of GDP at different concentrations so as to calculate mitochondrial state 3 respiration (ST3)

mitochondrial state 4 respiration (ST4)

respiratory control rate (RCR)

and the rate of oxidative phosphorylation (OPR). MMP was detected by Rhodamine 123 method at the different concentrations of GDP.      Results     With the increase of GDP concentration form 0 to 1.0 mmol/L

the values of ST3

ST4 and OPR were reduced while RCR was elevated. But when the concentration increased to 1.4 mmol/L

the former 3 indexes begun to increase while the later declined. When the GDP concentration reached to 1 mmol/L

the inhibitory rate was only 35.1%

51.3%

14.2% to ST3

ST4 and OPR respectively

while RCR was increased to 133.2%. No matter the concentration was over 1 mmol/L or under 1 mmol/L

the ability of inhibition was attenuated. MMP reached to the highest point when GDP exerted the highest inhibitory rate on mitochondrial respiratory oxygen consumption.      Conclusion     GDP

an inhibitor of UCP

s

can regulate the respiratory oxygen consumption and MMP of the isolated rat brain mitochondrial directly in a dose-effect fashion. The change of UCP

s

activity can affect the respiratory oxygen consumption and MMP.