A Novel Melatonin Antagonist, N-(2,4-Dinitrophenyl)-5-Methoxytryptamine Neutralizes Some Effects of Melatonin in the Female Syrian Hamster

Nordio, Maurizio; Vaughan, Mary K.; Zisapel, Nava; Migliaccio, Silvia; Jaarsveld, Anthea Van; Reíter, Russel J.

doi:10.3181/00379727-191-42926

Cited by 4 publications

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“…The lack of antagonistic potency of ML-23 and N-acetyltryptamine observed by us is not exceptional. Consistent with our findings is a rccent report by Nordio et al (1989) describing the inability of ML23 to counteract some melatonin actions when the drug was administered to living animals. There are some reasons to believe that this drug preferably interacts with peripheral rather than central sites of melatonin action (see Nordio et al, 1989).…”

Section: Table 1 Effkct Of Melatonin On Dopamine and Dopac Levels Insupporting

confidence: 92%

“…Consistent with our findings is a rccent report by Nordio et al (1989) describing the inability of ML23 to counteract some melatonin actions when the drug was administered to living animals. There are some reasons to believe that this drug preferably interacts with peripheral rather than central sites of melatonin action (see Nordio et al, 1989). On the other hand, N-acetyltryptamine was reported to behave as a partial agonist at the melatonin receptor (Dubocovich, 1985), and this might account for its ineffectivencss in the present work.…”

Section: Table 1 Effkct Of Melatonin On Dopamine and Dopac Levels Insupporting

confidence: 92%

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Melatonin Increases Serotonin N‐Acetyltransferase Activity and Decreases Dopamine Synthesis in Light‐Exposed Chick Retina: In Vivo Evidence Supporting Melatonin‐Dopamine Interaction in Retina

Nowak

Kazula

Gołembiowska

1992

Journal of Neurochemistry

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The administration of melatonin, either peripherally (0.01-10 mg/kg) or intraocularly (0.001-10 mumol/eye), to light-exposed chicks dose-dependently increased serotonin N-acetyltransferase (NAT) activity in retina but not in pineal gland. The effect of melatonin was slightly but significantly reduced by luzindole (2-benzyl-N-acetyltryptamine), and not affected by two other purported melatonin antagonists, N-acetyltryptamine and N-(2,4-dinitrophenyl)-5-methoxytryptamine (ML-23). The elevation of the enzyme activity induced by melatonin was substantially stronger than that evoked by 5-hydroxytryptamine, N-acetyl-5-hydroxytryptamine, or 5-methoxytryptamine. The melatonin-evoked rise in the retinal NAT activity was counteracted by two dopamine D2 receptor agonists, quinpirole and apomorphine, and prevented by the dopamine D2 receptor blocker spiroperidol, and by an inhibitor of dopamine synthesis, alpha-methyl-p-tyrosine. Melatonin (0.1-10 mg/kg i.p.) dose-dependently decreased the levels of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC), as well as the DOPAC/dopamine ratio, in chick retina but not in forebrain. The results obtained (1) indicate that melatonin in vivo potently inhibits dopamine synthesis selectively in retina, and (2) suggest that the increase in retinal NAT activity evoked by melatonin in light-exposed chicks is an indirect action of the compound, and results from the disinhibition of the NAT induction process from the dopaminergic (inhibitory) signal. The results provide in vivo evidence supporting the idea (derived on the basis of in vitro findings) that a mutually antagonistic interaction between melatonin and dopamine operates in retinas of living animals.

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Section: Table 1 Effkct Of Melatonin On Dopamine and Dopac Levels Insupporting

confidence: 92%

Section: Table 1 Effkct Of Melatonin On Dopamine and Dopac Levels Insupporting

confidence: 92%

Melatonin Increases Serotonin N‐Acetyltransferase Activity and Decreases Dopamine Synthesis in Light‐Exposed Chick Retina: In Vivo Evidence Supporting Melatonin‐Dopamine Interaction in Retina

Nowak

Kazula

Gołembiowska

1992

Journal of Neurochemistry

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Role de la glande pineale dans la regulation de l’axe hypothalamo-hypophyso-testiculaire

Nordio

Conte

Romanelli

et al. 1991

Androl.

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THE ROLE OF THE PINEAL GLAND IN THE REGULATION OF THE HYPOTHALAMO-PITUITARY-TESTI-CULAR AXIS. The role of the pineal gland and of its main hormone, melatonin, has not yet been clearly defined. The best known activity of the gland is antigonadal, at least in the experimental animals. In fact, the administration of melatonin or the modification of the light/darkness ratio, that is considered the most important regulatory mechanism of the melatonin-synthetic activity, leads to a gonadal regression by which all the morphological and hormonal parameters are modified. Such a mechanism is not operating in humans. However, data exist indicating a role for the pineal in this species. Our experimental data and those of the litterature indicate that the action of melatonin seems to be principally at the hypothalamic level, even though a direct action at the pituitary and gonadal levels cannot be excluded.

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Effects of Melatonin Agonists and Antagonists on Reproduction and Body Weight in the Siberian Hamster

Duncan

Fang

Dubocovich

1990

Journal of Pineal Research

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This study examined whether melatonin-induced inhibition of testicular weight and body weight in vivo could be antagonized by luzindole, a competitive melatonin receptor antagonist, or methysergide, a competitive serotonin receptor antagonist. Adult male Siberian hamsters were exposed to a long photoperiod (16L:8D) and given daily injections of drugs 3 h before lights off for 7 weeks. Hamsters treated with melatonin (0.375 mg/kg) exhibited testicular regression and loss of body weight. These effects were also marked in hamsters treated concomitantly with melatonin (0.375 mg/kg) and luzindole (10 mg/kg). In other studies, chronic injections of luzindole (30 mg/kg) to juvenile hamster failed to antagonize testicular regression induced by either melatonin injections or exposure to a short day photoperiod (12L: 12D). In contrast, concommitant injections of methysergide (6.25 mg/kg) and melatonin attenuated testicular regression and loss of body weight. When administered alone, neither luzindole nor methysergide affected testicular weight or body weight, whereas chronic injections of 5-methyoxyluzindole (10 mg/kg) mimicked the inhibitory effects of melatonin. 5-Methoxyluzindole inhibits 2-[125I]-iodomelatonin binding to median eminence/pars tuberalis membranes with an affinity similar to that of melatonin. Luzindole shows lower affinity for the inhibition of 2-[125I]-iodomelatonin binding than melatonin, which may explain why luzindole is not an effective melatonin receptor antagonist when administered in vivo. Methysergide, which has a very low affinity for inhibition of 2-[125I]-iodomelatonin binding, probably inhibits the effects of melatonin by blocking serotonergic neurotransmission.

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A Novel Melatonin Antagonist, N-(2,4-Dinitrophenyl)-5-Methoxytryptamine Neutralizes Some Effects of Melatonin in the Female Syrian Hamster

Cited by 4 publications

References 0 publications

Melatonin Increases Serotonin N‐Acetyltransferase Activity and Decreases Dopamine Synthesis in Light‐Exposed Chick Retina: In Vivo Evidence Supporting Melatonin‐Dopamine Interaction in Retina

Melatonin Increases Serotonin N‐Acetyltransferase Activity and Decreases Dopamine Synthesis in Light‐Exposed Chick Retina: In Vivo Evidence Supporting Melatonin‐Dopamine Interaction in Retina

Role de la glande pineale dans la regulation de l’axe hypothalamo-hypophyso-testiculaire

Effects of Melatonin Agonists and Antagonists on Reproduction and Body Weight in the Siberian Hamster

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