Low doses of exogenous melatonin in experimental diabetes: implications for the structure, function and antioxidant defense of rat testis and epididymis

Abstract

Oxidative stress is an important agent of systemic damage caused by hyperglycemia in diabetes. Experimental studies have shown that the neurohormone melatonin, due to its antioxidant properties, can combat oxidative stress in diabetes. However, most experimental studies use highly concentrated doses of this hormone and only evaluate its effects after the induction of diabetes, regardless of melatonin's role as a regulator of reproductive activity. For this present study, three goals were drawn. From treatment of rats with low doses of melatonin, over the pre-pubescent and pubescent period, we will evaluate: 1) the influence of oral administration of melatonin on testicular and epididymis structure, testicular esteroidogenic ability, sperm count and motility in adulthood, 2) changes in indicators of the status of antioxidant defense in the testis and epididymis and 3) the possible interferences on testis/ epididymis damage and antioxidant system caused by diabetes. It will be used five-week-old Wistar rats, to be distributed into the following groups (n = 15/group): Group C - nondiabetic control rats, Group M - nondiabetic control rats treated with melatonin; Group STZ - diabetic streptozotocin-induced rats and Group M + STZ - diabetic induced by streptozotocin rats and treated with melatonin. Melatonin will be administered in drinking water (2.5 mg / kg bw ethanol 0.001% per day) from the 5th week of age until death of the animals. Diabetes will be induced at 13 weeks of age by injection of streptozotocin (40mg/kg body weight, ip) and confirmed by blood glucose greater than 200mg/dl. The animals will be sacrificed at 21 weeks of age. The testis and epididymis will be processed for light microscopy analysis, followed by histological, stereological and histopathological evaluation for variations in their major tissue components. The motility of the sperm will be obtained at the time of death of the animals. The daily production of sperm will be evaluated by counting the final spermatids resistant to homogenization. The influence of melatonin and diabetes on testicular steroidogenic capacity will be studied by the Leydig cell activity, determined by the presence of the enzyme 17²-HSD and 3²-HSD, as well as testosterone levels. Changes in the activities of the main antioxidant enzymes (catalase, glutathione transferase and glutathione peroxidase) and lipid peroxidation levels in both the testis and in the epididymis will also be determined by specific biochemical reactions. The proposed analysis will certainly bring new insights to the interpretation of reproductive alterations that can affect individuals with abnormal levels of melatonin or subjected to treatment with this hormone. They can also provide more reliable information about the relationship between melatonin and reproductive impairment caused by diabetes. (AU)