GLUTAMATERGIC REGULATION OF [H-3] NORADRENALINE RELEASE IN THE MEDULLA-OBLONGATA OF NORMOTENSIVE AND SPONTANEOUSLY HYPERTENSIVE RATS

Objective: To assess in vitro the role of glutamate receptors in the r egulation of noradrenaline release from the medulla oblongata of normo tensive and hypertensive rats. Design and methods: The effects of L-gl utamate (an endogenous ligand for glutamate receptors), glycine (an al losteric agonist for the N-methyl-D-aspartate type of glutamate recept ors) and MK-801 (an antagonist for N-methyl-D-aspartate receptors) on [H-3]-noradrenaline release were examined in slices of rat medulla obl ongata. Results: L-Glutamate elicited [H-3]-noradrenaline release from slices of rat medulla oblongata in magnesium-free medium. Glycine als o increased the release of noradrenaline. Moreover, the effect of L-gl utamate on noradrenaline release was significantly potentiated by glyc ine. 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 alon e and in combination with L-glutamate increased the noradrenaline rele ase to a greater extent in SHR than in WKY rats.