Daily Rhythmic Changes in Kisspeptin Gene Expression and Testosterone Hormone in Male Syrian Hamsters ( Mesocricetus auratus )

In male Syrian hamsters, kisspeptin gene expression and testosterone changed rhythmically across the day: under a 16:8 light/dark photoperiod, Kiss1 mRNA and protein peaked in the light phase, and removing the pineal gland disturbed those rhythms. Switching to a short photoperiod also altered Kiss1 expression and testosterone. The results point to melatonin as a synchronizer of daily reproductive rhythms.

Journal article — controlled experimental study. Population: male Syrian hamsters (Mesocricetus auratus), pinealectomized or sham-operated, exposed to long or short photoperiods. Sample size: 192 male Syrian hamsters (48 per group). Follow-up: 30 days. Interventions: pinealectomy; long photoperiod (16L:8D); short photoperiod (8L:16D).

Under the long photoperiod (16L:8D), Kiss1 mRNA and protein varied significantly over the day and peaked during the light phase (P < 0.05). Pinealectomy disrupted these daily Kiss1 rhythms and caused altered testosterone levels. Under the short photoperiod (8L:16D), there was a marked change in Kiss1 expression and testosterone. The abstract does not report the magnitude of Kiss1 expression, testosterone concentrations, or melatonin levels.

For researchers studying Kisspeptin, this work provides evidence that daily Kiss1 rhythms in the hypothalamus depend on melatonin and photoperiod, at least in a seasonal rodent model. It links kisspeptin to testosterone regulation but does not establish the molecular pathway, receptor mechanism, or functional fertility outcomes.

Key findings

• Under a long photoperiod (16L:8D), Kiss1 mRNA expression and protein levels showed significant diurnal variation and peaked during the light phase (P < 0.05).
• Pinealectomy disrupted Kiss1 daily rhythms and led to altered testosterone levels compared with sham-operated hamsters.
• Under a short photoperiod (8L:16D), there was a marked change in Kiss1 expression and testosterone, although the abstract gives no direction or magnitude.
• The study used 192 hamsters divided into four groups of 48, with two pinealectomized groups and two sham-operated groups.

Limitations

• Abstract provides no numerical values for expression levels or hormone concentrations, limiting quantitative interpretation.
• Findings in Syrian hamsters may not translate to humans or other species.
• Only a 30-day photoperiod exposure was assessed; longer seasonal transitions were not covered.
• Pinealectomy is a broad surgical manipulation and does not isolate melatonin's receptor-level actions.

The record

• Journal: Zoological science 43(4): 388-396
• Published: 2026-08-01
• PMID: 42555223 — DOI: 10.2108/zs250118
• MeSH terms: Hypothalamus, Animals, Mesocricetus, Melatonin, Testosterone, RNA, Messenger, Gene Expression Regulation, Circadian Rhythm, Photoperiod, Cricetinae, Male, Kisspeptins
• Author countries: Turkey

Peptide profiles: Kisspeptin.

All indexed evidence: Kisspeptin trials & papers.

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