Effect of insulin on the expression of adiponectin and its receptors in the testes of type 1 diabetic rats

Abstract

Objective To explore the effect of insulin on the expression of adiponectin, adiponectin receptors, and adiponectin receptor-mediated signaling pathways in the testes of type 1 diabetic rats. Methods Thirty male 6- week Sprague - Dawley(SD) rats(body weight: 180- 200 g) were randomly divided into normal control group (group A,n=8) and streptozotocin injection group(n=22) by using random number table. Type 1 diabetic model was established by intraperitoneal injection of streptozotocin. Sixteen successfully- induced diabetic rats were randomly divided into diabetic group(group B,n=8) and diabetic treated with insulin(group C,n=8). Rats in group B were given subcutaneous protamine-zinc insulin in does of 3-5 U daily to control blood glucose at 10 mmol/L. The other two groups were given equal volume of normal saline daily. At the end of the eight-week of experiment, rats were sacrificed after blood samples were collected, and then the bilateral testes were collected quickly. Blood samples were used to detect the levels of biochemical index, insulin, adiponectin and sex hormone. Sperm number and motility were counted. The expression of testicular adiponectin, adiponectin receptors, adenosine 5'- monophosphate (AMP)- activated protein kinase(AMPK), protein kinase B(AKT), endothelial nitric oxide synthase(e- NOS), nitric oxide(NO), interleukin-6(IL-6), and tumor necrosis factor alpha(TNF-α) were assayed. Statistical analysis was performed by using LSD-t test and one way ANOVA. Results There were significant pathological changes in the testes of group B than those in group A. Compared with group A, the level of testes weight, sperm number and motility were decreased in group B(t=3.899, 21.139, 26.770, allP<0.05), the testicular adiponectin and its receptor 1, the ratio of p-AMPK to AMPK were significantly decreased in group B ((0.66±0.09) vs (1.00± 0.00), (0.68±0.05) vs (1.00±0.00), (0.34±0.11) vs (1.00±0.00),t=8.658, 14.297, 5.551, respectively, allP< 0.05); however, the level of the ratio of p-AKT to AKT, e-NOS in the testes were significantly increased in group B (1.54±0.27 vs 1.00±0.00, 1.56±0.26 vs 1.00±0.00,t=5.083, 4.997, respectively, bothP<0.05). These changes could be significantly reversed by insulin treatment. Compared with group B, the level of testes weight, sperm number and motility were increased in group C (t=3.444, 18.453, 23.103, allP<0.05); the level of adiponectin and its receptor 1, the ratio of p- AMPK to AMPK were significantly increased in group C (0.85±0.11 vs 0.66±0.09, 0.82±0.06 vs 0.68±0.05, 0.87±0.40 vs 0.34±0.11,t=4.969, 6.151, 4.454, respectively, allP<0.05); surely, the level of the ratio of p-AKT to AKT, e-NOS were significantly decreased in group B than those in group A (1.31±0.25 vs 1.54±0.27, 1.24±0.29 vs 1.56±0.26,t=2.169, 2.830, respectively, bothP<0.05). Conclusions Adiponectin and its receptors and adiponectin receptor-mediated signaling pathway may play an important role in testicular tissue injury in diabetic rats. Insulin may reduce the the degree of testicular tissue damage and produce the protective effect on testicular tissues in diabetic rats by regulating the expression of adiponectin, adiponectin receptors and adiponectin receptor- mediated signaling pathways. Key words: Diabetes mellitus, type 1; Adiponectin; Testes; Rats; Insulin