Effects of humanin on puberty and reproductive system in male rats

The reproductive system, influenced by some epigenetic and acquired factors, is primarily controlled by the HPG axis. Physiologically, reproductive capability is acquired with the onset of puberty. The reproductive health of an organism can be affected by various factors, all of which play a role in fertility. The reproductive system, particularly during puberty, is closely linked to energy metabolism. Hormones such as leptin, ghrelin, and irisin, which play a role in regulating energy metabolism, are known to directly affect the HPG axis. The effectiveness of humanin, a mitochondrial-derived peptide, on the axis is not yet fully understood. Humanin has been shown to be expressed in various tissues, including the testes and spermatozoa, and clinical studies indicate its concentration is associated with follicle size, serum reproductive hormone concentrations, and sperm motility. Experimental animal model studies have mainly focused on the cytoprotective role of humanin on spermatozoa. This study aims to elucidate the potential role of humanin in components of the reproductive system, such as puberty onset and sexual maturation, HPG axis hormones, sexual function, and reproductive tissues, with a particular focus on its impact on energy metabolism. To determine the onset of puberty, 21-day-old male Sprague-Dawley rats, weighing 35±2 grams, were divided into two groups (n=10): control and humanin. The control group received physiological saline, while the experimental group received 1 mg/kg/day dose of humanin via intraperitoneal injection for sixty days. Puberty onset in male rats is considered when the prepuce separates from the glans penis. Daily checks from the age of 30 days were conducted to determine the days of puberty entry. Rats that entered puberty were placed day alternate in the same cage with sexually active female rats for 30 minutes to determine first sexual behavior data and the timing of first sperm formation. Sexual function parameters were evaluated by applying CMT for 10 minutes in the seventh week and CDT for 30 minutes in the eighth week to rats that completed pubertal development. At the end of the experiment, serum samples were collected for ELISA analysis of reproductive hormone levels, sperm parameters were analyzed from epididymis samples, and reproductive tissues were histopathologically examined using the hematoxylin-eosin method. The application of humanin was found to advance the onset of puberty and parameters of sexual maturity, including the age of first sexual behavior display and first sperm appearance, in male rats. Additionally, the entry weight into puberty was higher in the humanin groups. Prolonged exogenous humanin application was determined to increase sexual motivation, elevate serum testosterone levels, and have a positive effect on sperm parameters in male rats. In conclusion, humanin was shown to play an active role in the reproductive system of male rats.