Kisspeptin-2 stimulates testicular function in adult pejerrey (Odontesthes bonariensis): Does it act directly on the testes?

Kisspeptin-2 (Kiss2) appears to act directly on the testes of adult pejerrey fish, not only through the brain. Injection of Kiss2 at 50 ng/g caused sperm release, and Kiss2-treated testicular tissue in vitro produced more androgens. Kiss2 was also found in spermatogonia, supporting a local role in the gonad.

Journal article — In vivo and in vitro experimental study. Population: Spermiating adult pejerrey (Odontesthes bonariensis) and testicular explants. Interventions: homologous Kiss2 (pjKiss2) intraperitoneal injection at 50 or 250 ng/g body weight; in vitro testicular explants exposed to pjKiss2 at 100 nM.

In vivo, pjKiss2 at 50 ng/g significantly decreased the testicular lobular area occupied by sperm compared with the 0 ng/g condition, indicating sperm release, and this was associated with a trend toward increased plasma androgen levels. In vitro, 100 nM pjKiss2 increased androgen levels in media from testicular explants after 6 h. Kiss2-expressing neurons were detected in the hypothalamus, Kiss2-immunoreactive fibers in the pituitary, Kiss2-expressing cells in the proximal pars distalis, and Kiss2 immunoreactivity in testicular spermatogonia. The authors conclude that Kiss2 can directly modulate testicular function and promote spermiation in pejerrey.

This paper matters to Kisspeptin researchers because it offers evidence for a direct intragonadal kisspeptin action in a teleost, separate from the classical hypothalamic GnRH pathway. It identifies Kiss2 immunoreactivity in spermatogonia and Kiss2-stimulated androgen release from testicular explants. It does not establish the receptor, downstream signaling, or whether such local actions occur in mammals or other teleosts.

Key findings

• pjKiss2 at 50 ng/g significantly reduced the testicular lobular area occupied by sperm in spermiating pejerrey, indicating sperm release.
• The sperm-release effect was associated with a trend toward higher plasma androgen levels.
• In vitro, 100 nM pjKiss2 increased androgen levels in media from testicular explants after 6 h.
• Kiss2-expressing neurons were present in the hypothalamus, consistent with previous reports in other teleosts.
• Kiss2 immunoreactivity was detected in testicular spermatogonia, suggesting a local gonadal action.
• Kiss2-expressing cells were also observed in the proximal pars distalis of the pituitary gland.

Limitations

• No sample size, variance measures, or statistical methods are reported in the abstract.
• The study was performed in a single teleost species, limiting generalizability to other fish or vertebrates.
• The in vitro explant approach cannot establish which specific testicular cell types mediate the androgen increase.
• The abstract does not report effects of the 250 ng/g dose or the time course beyond the 6-h in vitro measurement.

The record

• Journal: Comparative biochemistry and physiology. Part A, Molecular & integrative physiology 319: 112043
• Published: 2026-06-27
• PMID: 42364900 — DOI: 10.1016/j.cbpa.2026.112043
• Author countries: Argentina, USA

Peptide profiles: Kisspeptin.

All indexed evidence: Kisspeptin trials & papers.

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