6533b83afe1ef96bd12a77bd

RESEARCH PRODUCT

The Tuberohypophyseal Dopamine System: Dopaminergic Modulation of Vasopressin Release. Characterization of Release and Metabolism of3H-Dopamine

subject

description

Dopamine (DA) fibres originating in the arcuate nucleus project into the neural and intermediate lobes (N-IL) of the pituitary gland. It has been shown that DA and DA agonists decrease the electrically evoked vasopressin release from the isolated N-IL, an effect antagonized by D2 selective DA antagonists (see Holzbauer et al., 1983). However, there are also observations suggesting that there is an additional facilitation of the evoked vasopressin release via D1 receptors. Thus, SKF 82526 (6-chloro-7,8-drhydroxy-1-(p-hydroxyphenyl)-2,3,4,5-tetrahydro-1H-benzazepine mesylate) concentrationdependently decreased (max. 30 % at 30 nM) and increased (max. 40 % at 3 µM) the electrically evoked vasopressin release. The facilitatory action of SKF 82526 was antagonized in a concentration-dependent manner by flupenthixol but not by sulpiride (see Holzbauer et al., 1983). We now report that after depletion of the endogenous amine stores (by pretreatment with Ro 4-1284 (2-hydroxy-2-ethyl-3-isobutyl-9,10-dimethoxy-1,2,3,4,6,7-hexahydro-11-b-H-benzo(a)quinoIizine) 2 mg/kg i.p. 1 h before the experiments), the inhibitory effect of SKF 82526 disappeared and the facilitatory action of SKF 82526 was already seen at 30 nM.