The reproductive process requires the coordinated action of a large variety of peptides and steroid hormones, each one playing an important role in the normal functioning of the reproductive organs. In male bats, this control is linked to the correct functioning of the hypothalamic-pituitary-testicular axis, combined to the paracrine communication between Sertoli, Leydig and germ cells. The hypothalamus produces and secretes gonadotropin-releasing hormone (GnRH), which acts on the pituitary gland stimulating the production of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Both hormones act directly on the testicular somatic cells in order to stimulate and regulate their function and to control the spermatogenesis process. Testicular steroids (androgens and estrogens) in turn stimulate the seminiferous tubules and all secondary sex structures (epididymis and reproductive accessory glands, mainly the prostate), as well as provide feedback to the hypothalamus and pituitary. The hormonal regulation of bats differs interspecifically, with some species presenting the typical mammalian pattern; others showing unique variations, possibly imposed by the hibernation period; until species that have developed different adaptations, but without the imposition of a period of hibernation. One of these adaptations is the testicular regression, which is a deactivation process of the testicular tissue that is triggered by changes in the pattern of hormonal regulation. Thus, in this chapter, we seek to discuss different patterns of hormonal regulation of bats and some aspects of testicular regression.
Keywords: Androgen Receptor, Bat, Chiroptera, Estradiol, Estrogen, Hormonal Regulation, Reproduction, Spermatogenesis, Testicular Regression, Testis, Testosterone.