| The submandibular gland is a very important glandular organ with endocrine and exocrine for mammal. It can secret many bioactive substances such as epidermal growth factor, nerve growth factor and hepatocyte growth factor by endocrine in male. Previous studies showed that there were some receptors of these bioactive substances in testis. Moreover, the androgen receptors also existed in rat submandibular gland. The testis could affect some functions of submandibular gland by androgen secretion. So some researchers thought that there was a submandibular gland-testis axis besides hypothalamus-pituitary gland-testis axis in male mammal.Currently, researchs found that EGF was involved in spermatogenic function. EGF is a single polypeptide chain which is composed of 53 amino acid. It can increase the synthesis of protein and nucleic acid and promote proliferation and differentiation of cells. Wong's studies had shown: EGF overexpression could inhibit sperm production in mice. Tsutsumi's study found that level of serum EGF and epididymal sperm volume declined significantly after submandibular gland excision in mice. Analyzing the results of these studies, we found that submandibular gland may play an important role in spermatogenesis and sperm mature. Submandibular gland can secret EGF, NGF, HGF and other bioactive substances. Therefore, it is very necessary to investigate the effects of submandibular gland on spermatogenic function using an animal model of submandibular gland excision.Germ cell death has long been recognized as a significant feature of mammalian spermatogenesis. Spontaneous germ cell death is very important for the removal of germ cells and control of the quantity and quality of sperm. But excessive germ cell death will lead to diminish spermatogenic function and decrease the quality and quantity of sperm. Excessive germ cell death triggered by various regulatory stimuli, including deprivation of gonadotropins and intratesticular testosterone or by estradiol treatment in rats via apoptosis. Our studies showed that serum luteinizing hormone decreased significantly and serum testosterone increased markedly in rat after removing the submandibular gland. Meanwhile the sperm number in rat testis also decreased significantly after submandibular gland excision. We, hence, thought that excessive germ cell death maybe occurred in rat testis after removing the submandibular gland. In present experiments, we investigated the apoptosis of germ cells in rat testis using the in situ end labeling method (TUNEL). We also detected the changes of Bcl 2, Bax and caspase 3 expression in rat testis by Fluorescent Quantitative RT-PCR and Western blotting.Annexin 5, a calcium-dependent phospholipid binding protein, is one of the most important members in annexins superfamily. Annexin 5 have been distributed in rat Leydig cells and Sertoli cells. It may be involved in the synthesis and secretion of testosterone and inhibin B in rat testis. Testosterone played a critical role in the areas of the testis development, the sperm maturation and the maintenance of normal sexual function. Inhibin B is closely related to spermatogenesis and can reflect the level of spermatogenic function. Thus, annexin 5 might play an important role in the reproductive system by regulating the secretion of testosterone and inhibin B. The corresponding receptors of the bioactive substances secreted from the submandibular gland existed in rat Leydig cells and Sertoli cells. It seems that the substances secreted from the submandibular gland might control the expression of annexin 5 in rat testis. Therefore, in order to further understand the effects of annexin 5 on the male reproductive system, we investigated the change of annexin 5 expression in rat testis by fluorescent quantitative RT-PCR and Western blotting after removing submandibular gland in rats.Conclusion:1. Submandibular gland can adjust serum LH, T and other reproductive hormone levels, promote the normal development for testis and epididymis, reduce abnormal changes of the seminiferous tubule structure and maintain normal spermatogenesis by secreting much bioactive substance. 2. Submandibular gland can change the expression of Bcl 2 and Bax mRNA respectively, and further inhibit excessive apoptosis of spermatogenic cells to maintain normal spermatogenesis by secreting much bioactive substance.3. Submandibular gland plays an important regulatory role of annexin 5 in rat testis.
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