Adaption of Testosterone Secretion and LH Receptor Expression in Leydig Cells in High-Fructose-Fed Rats.

Abstract

Previous studies have demonstrated that the plasma testosterone level decreased in older insulin-resistance male patients. Both lower total testosterone levels and higher incidence of metabolic syndrome have also been reported. The aims of this study were to investigate the effects of high-fructose diet on testosterone release by Leydig cells and the activity of hypothalamus-pituitary-gonadal (HPG) axis in male rats. Male rats were fed with either standard chow (control group) or high-fructose diet (fructose-fed group) for 21 weeks. Hypertriglycemia, hyperinsulinemia and hypertension were observed in the fructose-fed group. Experimental rats were scarified and the plasma samples were collected for detecting the concentrations of plasma testosterone and luteinizing hormone (LH) by radioimmunoassay. Pure Leydig cells were prepared from adult male rats by continuous percoll gradient method. Sperm was separated from rat vas deferens and percent motility was evaluated under the microscope. The levels of plasma testosterone and LH decreased in the fructose-fed group as compared with the control group. Sperm motility was also reduced by 15 percent in the fructose-fed rats. In contrast, the basal release of testosterone from rat Leydig cells was not altered by fructose feeding. Besides, the testosterone release in vitro in response to different stimulants, including forskolin (an adenylyl cyclase activator, 10-5 M), 8-Br-cAMP (a permeable analogue of cAMP, 10-5 M), A23187 (a calcium ionophore, 10-5 M) or 25-hydroxy-cholesterol (water soluble cholesterol, 10-5 M) was not changed between the fructose-fed and control groups. Interestingly, the release of testosterone in response to human chorionic gonadotropin (hCG, 0.05 IU/ml) was enhanced by 8 folds in control group, but 11 folds in fructose-fed group. Protein expression of LH receptor in rat Leydig cells was also increased by feeding with fructose. These results suggested that the lower plasma levels of LH and testosterone in fructose-fed rats led to a higher sensitivity of hCG in Leydig cells. (poster)