Graduate Student Chica Enomoto in the doctoral program of the Graduate School of Environmental, Life, Natural Science and Technology and Associate Professor Takumi Oti and Professor Hirotaka Sakamoto of the Faculty of Environmental, Life, Natural Science and Technology, Okayama University, in joint research with Professor Masayuki Shimada of the Graduate School of Integrated Sciences for Life at Hiroshima University, have revealed for the first time in the world a dual-action mechanism by which intranasal administration of oxytocin, known as the happy hormone, simultaneously improves sexual motivation and sperm function in male rats. This demonstrates the potential for a new therapeutic strategy for sexual dysfunction. The findings were published in the electronic edition of The Journal of Sexual Medicine.
The diagram above illustrates the pathways of drugs administered intranasally.
The photograph below depicts an experiment involving the intranasal administration of oxytocin to male rats.
Provided by Okayama University
Until now, treatment for male sexual dysfunction has often focused on either central sexual desire decline or peripheral reproductive function, lacking a comprehensive approach.
The research group administered oxytocin intranasally to mature male rats and analyzed its effects on the central nervous system using immunohistochemical staining for phosphorylated ERK (pERK), a neural activity marker. As a result, they confirmed significant neural activation in hypothalamic neurons. In behavioral analysis, when sexually inactive male rats that did not achieve ejaculation during a 4-week sexual behavior training period were given intranasal oxytocin administration, mount latency and intromission latency were significantly shortened, and ejaculation latency also showed a tendency to shorten. Furthermore, the frequency of mounting, intromission, and ejaculation behaviors significantly increased compared with the control group.
Regarding effects on peripheral reproductive function, sperm function was evaluated using a computer-assisted sperm analysis (CASA) system in individuals that received chronic intranasal oxytocin administration for 1 week. As a result, sperm motility rate, progressive motility rate, and sperm count all significantly improved. Additionally, the weights of the epididymis, seminal vesicles, and prostate significantly increased, suggesting improvement in reproductive function. There were no changes in body weight and testis weight, revealing that oxytocin selectively enhances epididymal epithelial cell function and accessory sex gland activity.
The dual-action mechanism of oxytocin on both central and peripheral systems revealed in this study may provide an innovative therapeutic strategy for complex male sexual dysfunction that is difficult to resolve with conventional single-target treatments. In particular, it could be a groundbreaking approach that can address both problems with a single therapeutic intervention in patients who experience both reduced sexual motivation and decreased sperm function. Through future clinical research, it may be established as a new treatment option for patients for whom current treatments have limited effectiveness. Additionally, in the livestock industry, where methods such as electroejaculation for sperm collection are used, development into animal-friendly breeding management techniques is also conceivable.
Sakamoto commented: "Previous treatments for male sexual dysfunction have been dominated by approaches that focus on either central sexual desire decline or peripheral erectile dysfunction, as if forcing a choice between 'brain or lower body.' The dual-action mechanism of 'oxytocin' revealed in this study shows the potential for a groundbreaking therapeutic strategy that simultaneously improves both central and peripheral aspects and is expected to bring innovation to male sexual function medicine."
Enomoto commented: "I never expected such good results from the 'first step' of my graduation research. Moreover, gaining the opportunity to publish it as an international academic paper is a stroke of luck that can no longer be explained as 'beginner's luck.' I am deeply grateful to the professors who provided such careful guidance, and to my laboratory colleagues who worked diligently alongside me every day."
Journal Information
Publication: The Journal of Sexual Medicine
Title: Dual-action intranasal oxytocin enhances both male sexual performance and fertility in rats
DOI: 10.1093/jsxmed/qdaf228
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.