Unacylated ghrelin stimulates steroidogenesis in lean rats and reverses reproductive dysfunction in high fat diet-fed rats

Abstract

This study investigated the effect of sub-chronic administration of unacylated ghrelin (UAG) on steroidogenesis, sperm parameter, and reproductive function in lean and high fat diet (HFD)-induced obese male rats. Rats were divided into 4 groups (n = 12 each) as 1) Control-fed standard diets (STD): (10 kcal%), 2) STD + UAG (200 ng/kg, i.p.), 3) HFD obese: fed HFD (45 kcal%), and 4) HFD + UAG. Diet regimen was continued for 16 weeks after which normal saline as a vehicle or UAG was administered to desired groups for the next 4 weeks. In vitro, testicular slices were incubated with increasing concentrations of UAG (10^-8-10^-6 M) in the presence or absence of GSH-R1a antagonist, [D-Lys-3]-GHRP-6 (10^-6 M). UAG significantly increased the circulatory levels of FSH, LH and testosterone, increased testicular testosterone levels and sperm count and motility in lean and obese rats and reduced sperm morphological abnormalities and increased pregnancy rate and number of pups at birth in HFD-obese rats. Associated with the reduction in the final body and fat masses weights and independent of food intake, UAG post-therapy to both lean and HFD-fed rats significantly lowered fasting blood glucose and insulin levels, lowered HOMA-IR value, enhanced OGTT and ITT, lowered circulatory leptin levels, downregulated aromatase expression in adipose and testicular tissue and inhibited HFD-induced testicular oxidative stress and activation of cleaved caspase-3. Dysregulation of testicular levels of StAR, SF-1, CYP11A1 in the testis of both groups as well as in the in vitro preparation, in a dose-dependent manner, independent of GSH-R1a and not associated with activation of STAT3, a mediator of leptin signaling was apparent. In conclusion, administration of UAG can enhance reproductive function in lean rats and reverses HFD-induced reproductive dysfunction in obese rats. Abbreviations: AG: acylated ghrelin; BMI: body mass index; CHOL: cholesterol;FSH: follicular stimulating hormone; GHS: growth hormone secretagogues; GSH: reduced glutathione; HFD: high fat diet; HOMA-IR: homeostasis model assessment of insulin resistance: IR: insulin resistance; OGTT: oral glucose tolerance test; ITT: insulin tolerance test; LH: luteinizing hormone; MDA: malondialdehyde; STAT3: signal transducer and activator of transcription; SOD: superoxide dismutase; STD: standard diet; SF-1: steroidogenic factor-1; StAR: steroidogenic acute regulatory protein; CYP11A1: cholesterol side-chain cleavage enzyme (or P450scc); TGs: triglycerides; UAG: unacylated ghrelin.

Keywords: Ghrelin; HFD; obese; rats; sperm; steroidogenesis.