Failure of N-(2,4-dinitrophenyl)-5-methoxytryptamine (a putative melatonin antagonist) and of N-(3,5-dinitrophenyl)-5-methoxytryptamine to prevent the effects of injections of melatonin in the late afternoon on testicular activity of the golden hamster

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Abstract
Daily injections of 10 μg melatonin in the late afternoon into male golden hamsters kept under a long photoperiod (14 h light: 10 h darkness) and at low ambient temperature 6 ± 1 °C) induced a complete gonadal atrophy after 4 weeks. When administered under the same conditions at doses of 25 μg, neither N-(3,5-dinitrophenyl)-5-methoxytryptamine or N-(2,4-dinitrophenyl)-5-methoxytryptamine, a putative melatonin antagonist termed ML-23 in the literature, showed any effect on testicular activity. Moreover, these two drugs were also unable to prevent melatonin-induced gonadal atrophy when injected 30 min before melatonin. The results demonstrate that in the golden hamster and in the present experimental conditions, these drugs do not have the melatonin-antagonistic properties as described in the rat. Journal of Endocrinology (1989) 123, 243–247