These data are representative of cell-dependent, complex signaling networks interacting with the classic cAMP/PKA pathway for supporting the synthesis of steroid hormones. However, the activation of this intracellular signaling pathway may be triggered by all gonadotropins in target cells, where the intracellular cAMP increase is linked to other events such as trophic effects, mitotic functions, and sometimes apoptosis14. The physiological functions of gonadotropins are exerted via multiple signaling cascades simultaneously activated in the target cells. LH modulates proliferative and anti-apoptotic signals in granulosa cells, accompanied by androgen production in theca cells, and culminates in the induction of the dominant follicle ovulation and progesterone production by luteal cells6. During the fertile age, the action of gonadotropins is sex-specific and its secretion is regulated by a feedback mechanism depending on levels of sex steroid hormone. Despite these improvements, unanswered issues of gonadotropin physiology, such as the intrinsic pro-apoptotic potential to these hormones, the existence of receptors assembled as heteromers, and their expression in extragonadal tissues, remain to be studied. In healthy men, testosterone levels can change a lot from day to day, so a second test could be normal. The BTB is a unique structure consisting the gap junctions, tight junctions (TJs), desmosomes, and ectoplasmic specializations between Sertoli cells (Figure 1). The microenvironment created by neighboring Sertoli cells is vital for maintaining germ cell growth and initiating differentiation 3,4. The most optimal energy source for developing germ cells, the lactate molecule, is provided by Sertoli cells, which also furnish necessary growth factors and chemokines. There are somatic Sertoli cells and germ cells in the seminiferous tubules and Leydig cells, blood vessels, and immune cells in the interstitium. Understanding testis physiology is crucial for diagnosing and treating male reproductive disorders and infertility. The testes comprise multiple compartments, including the seminiferous tubules, interstitial cells (Leydig cells), and supporting cells (Sertoli cells). Therefore, having a thorough understanding of the hormonal regulation of testicular development and function is crucial for the accurate diagnosis and treatment of these disorders. These processes are fundamental for maintaining male fertility and overall reproductive health. The regulation of testosterone levels is governed by the negative feedback mechanisms of the HPG axis, as well as local factors within the testes. Testosterone is primarily synthesized and secreted by Leydig cells in the testes through a series of enzymatic reactions. After spermatogenesis is completed, mature sperm will be released from the basal part of the seminiferous epithelium into the seminiferous tubule lumen. The BTB is crucial for successful spermatogenesis as it helps safeguard developing sperm from autoimmune reactions. Consequently, it creates a specialized microenvironment that is immune-privileged and conducive to germ cell development . Progesterone increases the inhibitory effect of moderate oestrogen concentration levels on LH and FSH secretion. It acts on theca cells to produce progestins and androgens. After ovulation, LH binds to cells of the. Because H-hCG activates the receptor with lower activity than hCG and retains a highly proliferative potential9, it could be assumed that the hyperglycosylated gonadotropin modulates LH-like intracellular signaling patterns. The role of the exon 10–encoded receptor domain was highlighted by a clinical case describing a boy with impaired development of secondary sexual characteristics due to a naturally occurring deletion of the LHCGR exon 10151. This exclusive feature would rely mostly on the region encoded by the LHCGR gene exon 10, which may recognize and distinguish the molecular interaction between LH and hCG, modulating different hormone receptor conformations and intracellular signaling165,166. It was suggested that this complexity might serve for supporting a more complex mechanism of placentation and highly energy-demanding brain development in humans10 but this remains an unproven claim. Interestingly, treatment with OT has been found to increase the expression of proliferating cell nuclear antigen (PCNA) and B cell lymphoma 2 (Bcl-2) proteins in the testis, suggesting that OT may play an important role in the proliferation, survival, and death of germ cells . OT is a neurohormone stored and secreted by the posterior pituitary gland and has been found to be present in the male reproductive tract . Although studies have shown the effects of impaired PRL function on male reproduction, sexuality, and metabolism, the role of prolactin and its receptors in males is still unclear 144,149. Testosterone is the primary androgen in the male body, and its levels directly affect spermatogenesis . These cells contribute to the maintenance of the BTB and facilitate the proper development and release of mature spermatozoa. Additionally, the premature shedding of germ cells from Sertoli cells indicated a failure of spermatogenesis . During spermatogenesis, the germ cells undergo movement within the seminiferous epithelium, leading to the restructuring of the junctions between Sertoli cells and germ cells, as well as between Sertoli cells themselves at the BTB . Interstitial tissue contains Leydig cells, which are responsible for testosterone production, as well as blood vessels, nerves, and connective tissue. For example, the glial cell-derived neurotrophic factor (GDNF) produced by PMCs is instrumental in the development of undifferentiated spermatogonia cells in vivo . PMCs play a role in regulating sperm and luminal fluid transport and secrete growth factors and an extracellular matrix to uphold the niche of spermatogonial stem cells (SSCs). Cisgender, normal sexual orientation Normal testicular volume. Normal serum basal and GnRH stimulated FSH levels at 2 months of age. Infertility Microorchidism Normal basal testosterone, slightly elevated FSH and LH in the upper normal range. Macroorchidism Increased basal gonadotropins and testosterone. In males, GnRH from the hypothalamus stimulates the pituitary gland to release LH and FSH. However, the presence of this barrier also poses a challenge for the development of drugs that target the testicles. Additionally, two types of macrophages, peritubular macrophages, and interstitial macrophages, also contribute to testicular function . Infertility or reduced fertility can be attributed to endocrine diseases, testicular dysfunction, and poor lifestyle factors such as unhealthy diet and alcohol consumption. This large and sustained decline is now considered a major public health issue, and the relationship between sperm count and infertility has received widespread attention.
