COMPARISON OF THE EFFECTS OF THE DOPAMINE-D(2) AGONIST QUINELORANE ONTUBEROINFUNDIBULAR DOPAMINERGIC NEURONAL-ACTIVITY IN MALE AND FEMALE RATS

The purpose of the present study was to examine the effects of quinelo rane (LY163502), a potent and selective D2 dopaminergic (DA) receptor agonist, on the activity of tuberoinfundibular DA neurons in male and female rats as estimated by determining the concentration of the prima ry metabolite of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), in terminals of these neurons in the median eminence (ME). In males, quin elorane produced dose- and time-related increases in the concentration of DOPAC in the ME which was blocked by the D2 receptor antagonist ra clopride. The activity of tuberoinfundibular neurons in female rats is higher than it is in males because circulating levels of prolactin to nically stimulate these neurons in the female. In female rats, quinelo rane markedly lowered plasma concentrations of prolactin but failed to alter DOPAC concentrations in the ME. Pretreatment of female rats wit h prolactin antiserum induced hypoprolactinemia and reduced DOPAC conc entrations in the ME; in these animals quinelorane increased ME DOPAC concentrations. These results indicate that by acting on D2 receptors quinelorane is able to stimulate tuberoinfundibular DA neurons in both male and female rats, but in female rats the ability of quinelorane t o reduce circulating levels of prolactin indirectly reduces the activi ty of tuberoinfundibular DA neurons and thereby masks the stimulatory action of this drug on these neurons.