Low doses of exogen melatonin under experimental diabetes: implications for rat testicular and epididimal structure, function and antioxidant defense

Author(s)

Carolina Frandsen Pereira da Costa

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2014-07-31

Examining board members

Rejane Maira Góes; Glaura Scantamburlo Alves Fernandes; Raquel Fantin Domeniconi

• Advisor: Rejane Maira Góes

Abstract

There are numerous evidence that diabetes affects male reproductive function, causing damage to sperm parameters, and thus influencing the fertility of the affected individuais. Melatonin is a hormone secreted by the pineal gland and presents a wide range of actions, among them a key role in the control of steroidogenesis and in the protection against free radicais. The aim of this study was to evaluate whether melatonin offered orally at low doses, concomitant with sexual maturity, affects the reproductive parameters in healthy adult rats, and interfere with reproductive damage induced by experimental diabetes. Male Wistar rats were divided into eight groups (n = 15/group) at their fourth week of age: the first four were euthanized when they were 14 weeks old, being respectively- Control (CS) treated with melatonin (MS), diabetic (DS) and treated with melatonin subjected to diabetes (MDS); in turn, the last four were studied until they were 21 weeks-old - control (CL), treated with melatonin (ML), untreated diabetics (DL) and diabetics treated with melatonin (MDL). Melatonin was provided daily in drinking water (10 mg/kg b.w. in 0.001o/o ethanol/day) since the 5th week of age, while diabetes was induced at 13 weeks of age with a single dose of streptozotocin (4.5 mg I 100g bw, ip) in groups DS, DL, MDS and MDL. Subgroups from the first experimental design(Groups S) had a diabetic period accounting for one week, while subgroups from the second one (Groups L) were submitted to two months of the disease. Diabetic rats presented hyperglycemia, marked reduction in body weight, strongly decreased circulating levels of testosterone, and at late disease conditions, epididymal atrophy. Histological and stereological analysis indicated alterations in the interstitial compartment of the testis, premature germ cell detachment and vacuolization of Sertoli cells, but more severe injuries, such as depletion of the germinal epithelium were observed in only one animal after two months of illness. Furthermore, there was no damage to the daily sperm production. Sperm counts were reduced at the epididymis distal segment, and transit time was accelerated in all segments after the progression of the disease. Sperm motility was impaired, and the number of aberrant cells in the lumen of the epididymal duct was markedly higher than in healthy animais. There was a thickening of the stromal tissue in some segments, with increased frequency of collagen fibers and smooth muscle. Diabetes has led to an increase in systemic leveis of glutathione peroxidase (GPx) and malondialdehyde (MDA) levels, which were not restored by melatonin supplementation. The activity of glutathione transferase (GST), in turn, was reduced in the blood of diabetic animais regardless of the treatment with melatonin. ln the testis, there were marginal changes in antioxidant systems related to diabetic condition, which did not occur in the epididymis. Treatment of healthy animais with melatonin from pre-pubertal age did not cause reproductive disorders in adulthood, although it lead to a reduction in serum testosterone levels, and did not alter biomarkers related to antioxidant response. However, melatonin treatment previous and concomitant with the diabetic condition prevented some damages associated with this disorder, particularly in what refers to the epididymis, since the short-term ingestion prevented sperm reserve impaiments, and attenuated damage to sperm motility in both periods, although it did not prevent the atrophy observed in the distal segment. Regarding the histology of the organ, melatonin seemed to prevent the development of flbrosis in its stroma, although this response was conflned to particular sub-regions. The ingestion of melatonin also avoided severe injury to the germinal epithelium, and prevented morphological changes in Leydig cells. Steroidogenesis was not as impaired as in untreated diabetics, and this pattern was accompanied by a signiflcant increase of AR-positive cells in the testis of diabetic individuais treated in long term. Therefore, our evidence suggests that the daily intake of 10 mg/kg b.w. melatonin offered from pubertal period on does not impair testicular or epididymal functions, but has a positive effect on the secretion of testosterone, which is affected by diabetes. The reduction in steroidogenesis caused by ingestion of melatonin was permanent, therefore our data suggest that prolonged MLT consumption leads to a reprogramming of Leydig cells or hypothalamic-pituitarygonadal axis. The ingestion of melatonin also preserves sperm motility, but nor epididymal atrophy or restores sperm reserves. Comparing the long term effects with the acute experimental diabetes, it appears that melatonin acts differentially in accordance with the development of the disease (AU)

• FAPESP's process: 13/07210-0 - Low doses of exogenous melatonin in experimental diabetes: implications for the structure, function and antioxidant defense of rat testis and epididymis
• Grantee: Carolina Frandsen Pereira da Costa
• Support Opportunities: Scholarships in Brazil - Master