الفهرس 
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Abstract
This work was devoted for the investigation of the possible protective effect of melatonin, NAC in different doses and their combination in testicular toxicity of rats induced by nicotine. LD50 of nicotine was evaluated before induction of the testicular toxicity in rats. br Fifty four old male rats were divided randomly into nine groups (six rats each). First -#103;-#114;-#111;-#117;-#112; served as negative control with saline. Second -#103;-#114;-#111;-#117;-#112; received only nicotine (1 mg/kg) as positive control group. Remaining groups except last one were injected with nicotine (1 mg/kg/day i.p) at the same day as i.p administration of either melatonin (5 mg and 10 mg/kg), NAC (100 mg and 200 mg/kg), combined low doses of melatonin and NAC and combined high doses of melatonin and NAC. Ninth and last -#103;-#114;-#111;-#117;-#112; received nicotine for one month and stop it for another month. br At the end of the four weeks, all rats were sacrificed by decapitation and blood samples were collected for biochemical and hormonal analysis. The caudal epididymis of both testes were dissected and sliced in buffered solution for sperm extraction and counting. Testicular tissue sections were prepared for pathological evaluation of spermatogenesis. br Administration of nicotine (1 mg/kg) for four weeks i.p produced significant reduction of total antioxidant capacity, testosterone and LH hormones with insignificant change in serum level of FSH. Additionally, nicotine administration showed significant reduction of sperm count. Nicotine provoked some histopathological changes in the testis such as focal detachment of the basal spermatogenic cells -#102;-#114;-#111;-#109; their basement membrane, these changes were -#99;-#104;-#97;-#114;acterized by frequent deficiency of elongated spermatids and mature spermatozoa in seminiferous tubules nicotine treated rats. br Low and high dose of melatonin (5 mg/kg and 10 mg/kg) produced antioxidant effect by significant elevation of TAC, while both doses of melatonin produced insignificant change in serum levels of testosterone, FSH and LH. Additionally low and high doses of melatonin increase number of sperm count significantly after treatment for four weeks. Treatment with low dose melatonin (5 mg/kg) showed insignificant changes of percentages of tubules with mature spermatogenesis. However, high dose of melatonin (10 mg/kg) showed a significant rise of percentage of tubules that had mature sperms in comparison to positive control rats. br Results of the present study revealed that administration of low dose of NAC (100 mg/kg) induced a significant increase of TAC, while low dose produced insignificant change in serum levels of testosterone, FSH and LH. Treatment with high dose NAC (200 mg/kg) induced a significant rise of TAC and serum testosterone level, while there were no significant changes of serum levels of FSH or LH after administration of high dose NAC. Administration of two different doses of NAC succeeded to increase of the sperm count significantly in comparison to positive control rats, while treatment with both low and high doses of NAC showed insignificant change of percentages of tubules with mature spermatogenesis. br Concurrent administration of combined low doses of melatonin (5 mg/kg) and NAC (100 mg/kg) induced a significant increase of both TAC and serum testosterone levels. On the other hand, combined low doses of melatonin and NAC produced insignificant change in serum levels of both FSH and LH. Combination of high doses melatonin (10 mg/kg) and NAC (200 mg/kg) induced a significant increase of both TAC and serum testosterone levels, while administration of combined high doses of melatonin and NAC produced insignificant change in serum levels of both FSH and LH. br Treatment with combined low doses of melatonin (5 mg/kg) and NAC (100 mg/kg) as well as treatment with combined high doses of melatonin (10 mg/kg) and NAC (200 mg/kg) showed significant rise of sperm count and percentages of tubules with mature spermatogenesis. br Withdrawal of nicotine resulted in a significant increase of TAC, as well as serum testosterone level increase significantly when compared to positive control rats. While nicotine withdrawal produced insignificant changes in serum levels of FSH and LH. Nicotine withdrawal induced a significant increase of sperm count and the percentages of seminiferous tubules with mature sperms increased to a level that is comparable to normal rats’ values. br In conclusion; Nicotine administration produced testicular toxicity; this toxicity can be reduced by administration of melatonin, NAC or their combination in low and high dose. Combination of melatonin and NAC in high dose produced response similar to nicotine withdrawal results. But smoking cessation still is the best choice to avoid testicular dysfunction caused by smoking as it is safe method.