Testosterone [KLH]

Testosterone is a steroid hormone that is anabolized in the body and is the main component of androgens. The production and secretion of testosterone is closely related to age, and is mainly produced by testicular interstitial cells and regulated by the hypothalamic-pituitary-testicular interstitial cell axis. It peaks at puberty under the stimulation of luteinizing hormone and then tends to decline with age. Testosterone is important for spermatogenesis and follicular development. Testis receptors are widely distributed in the testes, nervous system, atrial and ventricular muscles, kidneys and adrenal glands, and even in the circulatory system in vascular endothelial cells, smooth muscle cells, cardiac muscle fibers, and other cells as well, which makes testosterone has an indispensable role in maintaining normal physiological activities in other tissues and organs as well as in the body's mental activities.

Figure 1. Targets for medical therapies on the hypothalamic-pituitary-gonadal axis
(Source: Lo EM, et al. 2018)

Changes in testosterone expression levels are closely related to gonadal function. Male hypogonadotropic hypogonadism is a hypogonadal disorder caused by the underproduction or overconsumption of androgens or the inability to fulfill their physiological roles. Testosterone levels in older men decline progressively with age and fall below the normal range for healthy men causing delayed hypogonadism with a range of clinical signs and symptoms of androgen deficiency. These symptoms are generally accompanied by decreased serum total and free testosterone levels in men. In addition, testosterone affects a wide range of physiological functions in the body. For example, low total testosterone levels have been linked to an increased risk of developing diabetes, and it has been found that decreased testosterone levels may contribute to the development of diabetes in men by affecting mitochondrial function, while low testosterone levels are also more likely to be insulin-resistant, making them more susceptible to developing type 2 diabetes. Because testosterone receptors are widely distributed in the body, current research has demonstrated a link between testosterone concentration levels and diseases such as lung cancer, apnea syndrome, and hypohemoglobinemia.

Testosterone replacement therapy (TRT) is the primary treatment for testosterone deficiency in male patients. In prepubertal androgen-deficient male adolescents, TRT is primarily to stimulate and maintain the development of male secondary sexual characteristics and the development of somatic and sexual functions, whereas in adult males TRT is primarily to restore and maintain libido, sexuality, and secondary sexual characteristics. The main testosterone-related preparations currently available include androgen analogs, androgen antagonists, etc. The testosterone preparations available on the market are oral, oral mucosal, intramuscular, and subcutaneous implants.