Influence of the oestrous cycle on L-glutamate and L-aspartate transport in rat brain synaptosomes

Oestrous cycle and sex differences in sodium-dependent transport of L-[H-3] glutamate and L-[H-3]aspartate were investigated employing well washed syna ptosomes prepared from rat brain cortex. Transport was best analysed on the basis of two components, a high and low affinity transport site. Oestrous cycle and ses differences were observed for both substrates. The high affin ity transporter displayed highest affinity for glutamate transport in synap tosomes from female rats during proestrous and oestrous. This differed sign ificantly from glutamate transport during dioestrous and in male rats. High affinity aspartate transport displayed highest affinity during oestrous an d differed significantly from transport during dioestrous. Maximal velocity of high affinity glutamate transport was higher in synaptosomes from femal es during dioestrous compared with oestrous and loner in synaptosomes from male rats when compared with Female rats in dioestrous and metoestrous. The low affinity sodium-dependent glutamate transporter displayed a IO-fold hi gher affinity for glutamate during proestrous than during the other three p hases of oestrous and in male rats. Exogenously applied oestradiol and prog esterone to synaptosomes from male rats showed no effect on glutamate or as partate transport. No acute effect of oestradiol or progesterone on glutama te currents in oocytes expressing EAAT1 or EAAT2 subtype of glutamate trans porter was observed. These results suggest hormonal regulation of high and low affinity sodium-dependent excitatory amino acid transporters over the f our day oestrous cycle in synaptosomes from rat cortex. This regulation is unlikely to be due to a direct effect of oestradiol or progesterone on glut amate transporters. (C) 1999 Elsevier Science Ltd. All rights reserved.