Adiponectin and Resistin Adipokines: Implication in Testosterone Hormone Secretion in Obese Male Rats

Background: Obesity in men, particularly when central, is associated with lower total testosterone [TT], free testosterone [FT] and sex hormone-binding globulin [SHBG], and a greater decline in TT and FT with increasing age compared with lean men. Obesity-related conditions such as obstructive sleep apnea, insulin resistance and type 2 diabetes mellitus are independently associated with decreased plasma testosterone. Obese men have reduced sperm concentration and total sperm count compared to lean men but sperm motility and morphology appear unaffected. The cause and effect relationships between low plasma androgen levels, obesity and the metabolic syndrome remain unclear. Adiponectin has a role in the control of the reproductive axis, which might operate as endocrine integrator linking metabolism and gonadal function. Expression, regulation and functional role of adiponectin and resistin adipokines in rat testis were documented. Both adipokines may operate as novel endocrine integrators linking energy homeostasis and reproduction. Objective: The aim of the present study was to find out an effect of obesity on testicular mRNA gene expression of adiponectin and/or resistin adipokines. Also, to investigate a potential correlation between the mRNA expression of adiponectin and/or resistin and testicular function as indicated by serum testosterone level in obese male rats. Material and Methods: The study was conducted on 20 male albino rats. The experimental animals were divided into 2 groups, 10 rats each. Group I: Control rats and Group II: Obese rats. After 12 weeks, all overnight-fasting rats were sacrificed. Blood samples were collected, and the testes were rapidly excised, weighed and frozen at –80oc for further mRNA detection. The following parameters were measured: Serum fasting glucose, fasting insulin, fasting triglycerides, fasting cholesterol, insulin resistance was estimated using homeostatic model assessment (HOMA) index, serum testosterone, testicular resistin mRNA expression and testicular adiponectin mRNA expression. Results: The results of the present work showed that serum glucose, triglycerides, total cholesterol, and insulin resistance were significantly higher in obese rats compared to the controls. Serum testosterone level and testicular adiCorrespondence to: Dr. Hanan A. Mubarak, The Department of Physiology, Faculty of Medicine, Cairo University. ponectin mRNA were significantly lower in obese rats, while testicular resistin mRNA was significantly higher in obese rats compared to the control. No correlations were found between testicular resistin, adeponectin, and serum testosterone in the two studied groups. Conclusion: The present study provided a characterization of the pattern of gene expression of both adipokines: Resistin and adiponectin in the testis and showed their association with gonadal function on the basis of the level of serum testosterone. This inter-relation could suggest the biological effects of these adipokines in the male gonad.