Maintaining adult male golden hamsters in short daily photoperiods (1 hr of light and 23 hr of darkness daily; LD 1:23) for 12 weeks caused the testes and accessory sex organs to atrophy and also led to significant depressions in pituitary LH and prolactin levels. If hamsters that were kept in LD 1:23 cycles received weekly subcutaneous implants of either a melatoninbeeswaxor a 5-methoxytryptophol-beeswax pellet (1 mg indole in 24 mg beeswax) the testes and accessory sex organs failed to involute and pituitary LH levels did not drop. Both treatments also retarded the depression in hypophyseal prolactin levels. Treatment (twice daily on weekdays and once daily on weekends) with 1.5 μg injections of synthetic LRH (in 0.2 ml 8% gelatin) did not prevent gonadal or accessory organ atrophy while it further depressed hypophyseal LH stores. Following LRH treatment, plasma LH titers were significantly elevated. The reproductive organs of hamsters that were moved from short (LD 1:23) to long (LD 14:10) daily photoperiods regeneratedwithin 8 weeks. This light-induced restoration of the gonads was not prevented or retarded by the weekly implantation of either melatonin-beeswax or 5-methoxytryptophol-beeswax pellets. The results suggest that in the male golden hamster neither melatonin nor 5-methoxytryptophol accounts for the antigonadotrophic activity of the pineal gland.
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