Glutamatergic regulation of [3H]-noradrenaline release in the medulla oblongata of normotensive and spontaneously hypertensive rats


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Abstract

ObjectiveTo assess in vitro the role of glutamate receptors in the regulation of noradrenaline release from the medulla oblongata of normotensive and hypertensive rats.Design and methodsThe effects of L-glutamate (an endogenous ligand for glutamate receptors), glycine (an allosteric agonist for the N-methyl-D-aspartate type of glutamate receptors) and MK-801 (an antagonist for N-methyl-D-aspartate receptors) on [3H]-noradrenaline release were examined in slices of rat medulla oblongata.ResultsL-Glutamate elicited [3H]-noradrenaline release from slices of rat medulla oblongata in magnesium-free medium. Clycine also increased the release of noradrenaline. Moreover, the effect of L-glutamate on noradrenaline release was significantly potentiated by glycine. MK-801 inhibited the increase in noradrenaline release evoked by L-glutamate. In spontaneously hypertensive rats (SHR) the facilitatory effect of L-glutamate on noradrenaline release was significantly more pronounced than in Wistar-Kyoto (WKY) rats. Furthermore, glycine alone and in combination with L-glutamate increased the noradrenaline release to a greater extent in SHR than in WKY rats.ConclusionThe present results show that the excitatory amino acids might increase noradrenaline release from rat medulla oblongata, which was partially dependent on the N-methyl-D-aspartate type of glutamate receptors. The greater effect of L-glutamate and glycine in SHR suggests that these amino acids might be involved in the regulation of noradrenaline release in the medulla oblongata of hypertension.

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