Endocrine characterization of the new dopamine autoreceptor agonist roxindole

Roxindole (5-Hydroxy-3-(4-phenyl-1,2,3,6-tetrahydropyridil-(1)-butyl)-indol) is a newly developed compound with a high dopamine autoreceptor agonistic potency at D2 receptors. Evaluation of roxindole for clinical purposes in psychiatric patients revealed that the substance has contrary to expectation merely negligible antipsychotic but considerable antidepressive effects. Interestingly it is nearly devoid of any side effects. To further characterize the endocrine effects, 1 mg roxindole was applied at 09:00 to 6 male volunteers and the effects compared to placebo. From 08:00 to 13:00 blood samples were drawn every 30 min. No effect on adrenocorticotropin and cortisol secretion was observed, neither mean plasma concentrations nor area values differed significantly. 90 min after roxindole administration an enhanced release of growth hormone could be observed, comparison of mean hormonal concentration revealed statistical significance (p < 0.05). Also the area values differed significantly (roxindole vs. placebo mean +/- SD 18.1 +/- 17.1 vs. 7.7 +/- 8.0 micrograms x h/l; p < 0.05). After roxindole also a pronounced reduction of prolactin plasma levels from 5.3 +/- 1.4 micrograms/l to 1.1 +/- 0.4 microgram/l within 150 min could be observed. Mean plasma concentrations (p < 0.05) and area values differed significantly (roxindole vs. placebo mean +/- SD 14.8 +/- 13.5 vs. 34.4 +/- 18.1; p < 0.05). Roxindole had no effect on blood pressure parameters and heart rate. The major findings of the present exploratory study are, that roxindole has potent effects on the facilitation of growth hormone secretion and the inhibition of prolactin release. Both findings are complementary and point also to interesting postsynaptic dopamine receptor agonistic effects.