Mechanisms of cannabinoid receptor 1 in reproductive toxicity induced by DBP exposure in male rats

Objective To explore the expression pattern of cannabinoid receptor 1 (CBR1) in reproductive toxicity induced by dibutyl phthalate (DBP) exposure in male rats, and investigate the underlying mechanism. Methods Sixty healthy male Sprague-Dawley rats were randomly divided into 4 groups (15 animals in each group), that is, control group, and low-, medium- and high-dose groups, exposure to 100, 250 and 500 mg/kg DBP, respectively, by intragastric injection daily for 28 consecutive days. Computer-aided sperm analysis system (CASA) was used to detect sperm vitality, concentration, and rate of deformity. HE staining was employed to observe the changes in testicular tissue. The serum levels of testosterone (T), estradiol (E2), luteinizing hormone (LH), follicle stimulating hormone (FSH) and sex hormone binding protein (SHBG) were measured by ELISA. The expression of p38, ERK, AKT and CBR1 at mRNA and protein levels was measured by RT-PCR and Western blotting. Results Compared with the control rats, the sperm motility and total sperm motility were reduced in low- (20.1±9.2 and 73.6±3.2), middle- (22.3±6.2 and 40.7±24.4) and high-dose (21.0±14.2 and 41.2±4.6) exposure groups (P < 0.05). Sperm concentration was significantly lower in the high-dose group (152.0±67.0, P < 0.05). Compared with the control group, serum T levels were significantly lower in the middle- (19.65±2.65) and high-dose groups (17.40±3.50, both P < 0.05). The serum level of E2 was significantly decreased in each exposure group (2.09±0.08, 2.11±0.77, 2.05±0.02) when compared to the control group. So were the serum LH levels (7.80±1.42, 7.68±2.28, 6.43±0.90) (all P < 0.05). While the serum level of FSH was all significantly increased in each exposure group (2.88±0.37, 2.89±0.29, 3.37±0.30), when compared to the control group (P < 0.05). In the testis tissue, the expression of CBR1 was increased at mRNA and protein levels than that of the control group, and the expression of p-p38 and p-ERK was significantly decreased than the control group (P < 0.05). Conclusion DBP exposure results in impairment of testicular tissue structure and decrease of sperm motility in male rats, which may be due to the up-regulation of CBR1 and the subsequent inhibition of ERK/p38MAPK phosphorylation.