The effects of androgenic steroids on the dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) contents of different brain regions have been studied in order to elucidate the possible involvement of neurotransmitters in the negative feedback action of androgens. Administration of testosterone propionate (TP); (100 μg/kg or 5 mg/kg, i.p.) increased plasma testosterones, which reached a maximum at about 30 min following injections. TP (100 μg/kg) decreased the DA level in the hypothalamus to a minimum after 30 min and returned to normal level after 120 min. There was no effect in the amygdala, striatum and mesencephalon. Subsequent to 5 mg/kg i.p. TP administration, the minimum in the DA level was observed between 90 and 120 min in the hypothalamus, and after 120 min in the amygdala, but the treatment was without effect in the striatum and mesencephalon. Both doses of TP were ineffective as regards for in altering NA and 5-HT levels in the brain areas studied. In a dose of 5 mg/kg, androgens of different activities, such as norandrostenolone, dihydrotestosterone and androstenedione, decreased the DA contents of the hypothalamus and amygdala regions, but pregnenolone was ineffective. None of the androgens affected the NA and 5-HT levels in the brain areas studied. The data suggest that some of the actions of androgens are mediated via a dopaminergic mechanism in which not only the hypothalamus but also the amygdala is involved.

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The effects of different neurotransmitters were tested in vitro on a hypothalamic tissue, collagenase-digested isolated anterior pituitary and Leydig cell suspension system by measuring the testosterone production of the Leydig cells. Neurotransmitters were used in concentrations of 0.25, 1.0, 2.5, 5.0, and 10.0 pg/ml incubation medium. Dopamine in doses of 1.0, 2.5, and 5.0 pg/ml increased the hypothalamic tissue-induced pituitary-testis activation, while it had no direct effect on pituitary and Leydig cells. Noradrenaline in the concentration range 2.5-10.0 pg/ml decreased the luteinizing-hormone-releasing-hormone (LHRH) sensitivity of the pituitary cells. 5.0 and 10.0 pglml 5-hydroxytryptamine decreased the testosterone production and the hCG sensitivity of the isolated Leydig cells. Carbamylcholine and pilocarpine had no action on the in vitro system at the different levels studied.