Presynaptic mediation by alpha 2-, beta 1- and beta 2-adrenoceptors of endogenous noradrenaline and dopamine release from slices of rat hypothalamus.

Using high performance liquid chromatography with an electro-chemical detector, we studied effects of different compounds on the impulse-evoked release of endogenous noradrenaline (NA) and dopamine (DA) release from slices of the rat hypothalamus. Adrenaline (10(-7) M), with a potent alpha-agonistic action decreased both NA and DA release, and these effects were blocked by pretreatment with yohimbine (10(-7 M). The alpha 2-antagonist, yohimbine alone (10(-8) - 10(-6) M) concentration-dependently increased these releases, while alpha 1-antagonist, prazosin showed weak increase on NA but not DA release at 10(-6) M. Isoproterenol (10(-10) - 10(-8) M) concentration-dependently increased these releases and the effects were antagonized by pretreatment with a non-selective beta-antagonist, 1-propranolol, a beta 1-antagonist, atenolol or a beta 2-antagonist, butoxamine. 1-Propranolol (3 X 10(-7) M) alone, but not the d-isomer inhibited the releases. Thus, in the rat hypothalamus, the release of NA and DA may be mediated via presynaptic alpha 2-, beta 1- and beta 2-adrenoceptors.