The review delves into the roles of steroid hormones in testicular function, emphasizing their interactions with intracellular nuclear receptors. These hormones act through various cellular pathways and receptor types, emphasizing the need for a multifaceted research approach to understand their critical roles in testicular function. In the absence of testosterone or functional androgen receptors (AR), males are infertile because spermatogenesis rarely progresses beyond meiosis.3–5 The male generative glands also contain Sertoli cells, which require testosterone for spermatogenesis. Free testosterone (T) is transported into the cytoplasm of target tissue cells, where it can bind to the androgen receptor, or can be reduced to 5α-dihydrotestosterone (5α-DHT) by the cytoplasmic enzyme 5α-reductase. For women with PCOS, hormones like birth control pills can be used to help lessen the effects of this increased level of testosterone. In males, these are usual late pubertal effects, and occur in women after prolonged periods of heightened levels of free testosterone in the blood. Consequently, AMH levels are invaluable in differential diagnosis, particularly for conditions such as bilateral cryptorchidism and anorchidism in boys with nonpalpable gonads 119,120,124. The AMH assay demonstrates high sensitivity, up to 92%, in detecting the absence of testicular tissue . In a clinical setting, patients who have undergone hypophysectomy for pituitary tumors may still exhibit autonomous spermatogenesis due to the ligand-independent, constitutive activation of FSHR . The cAMP/PKA signaling pathway plays a pivotal role in the regulation of FSH on the maintenance of the spermatogonia pool and the differentiation and apoptosis of spermatogonia. For example, transcription factors including Krüppel-like factor 4 (KLF4) , nuclear factor (NF)-κB , and activator protein-1 (AP-1) are involved in the regulation of Sertoli cell differentiation by FSH. On the one hand, the lack of AR signals leads to the dysfunction of the chromosome, mainly manifested in the tissues with double-strand breaks (DSBs) repair and chromosome synapsis . Even in women without complete anovulation, elevated insulin creates less than optimal conditions for follicle development and ovulation, potentially contributing to irregular cycles or poor egg quality. In women with substantial insulin resistance, this interference can be sufficient to prevent ovulation entirely. For women, this cascade is complicated further by the cyclical nature of estrogen and progesterone, which interact with blood sugar regulation in ways that create changing nutritional needs across the month. When you consume foods that cause rapid blood glucose spikes, you trigger a cascade of hormonal responses that ripple through your entire endocrine system. Additionally, we synthesize the current understanding of testosterone as a key messenger promoting metabolic homeostasis in preclinical models and humans. The same research found fathers (outside competitive environments) had the lowest testosterone levels compared to other males. Physical presence may be required for women who are in relationships for the testosterone–partner interaction, where same-city partnered women have lower testosterone levels than long-distance partnered women. Falling in love has been linked with decreases in men's testosterone levels while mixed changes are reported for women's testosterone levels. There is no FDA-approved androgen preparation for the treatment of androgen insufficiency; however, it has been used as an off-label use to treat low libido and sexual dysfunction in older women. In accordance with sperm competition theory, testosterone levels are shown to increase as a response to previously neutral stimuli when conditioned to become sexual in male rats. It has been proven in clinical trials to be a highly reversible, effective, and safe male contraceptive, with a total efficacy was about 95% . Testosterone undecanoate (TU), a testosterone ester created by the fatty acid esterification of testosterone, has been approved for use in several countries. There are not many reversible contraceptive methods available to men, including the male condom and withdrawal, with failure rates of 13% and 20%, respectively . This suggests elevated estrogen levels do not significantly hamper testicular function (Rochira and Carani, 2009; Bulun, 2014; Miedlich et al., 2016). For instance, treatment with the aromatase inhibitor letrozole led to a reduction in testicular cortisol levels, inversely increasing Sertoli cell proliferation (Berger et al., 2019). An interesting relationship between the decline in endogenous estrogen and testicular cortisol has been observed, hinting at an interconnected signaling pathway impacting Sertoli cell proliferation. The most prominent expression was observed in the nucleus of pachytene spermatocytes, but ER expression was also evident in spermatogonia, preleptotene spermatocytes, round spermatids, and Sertoli cells (Takada et al., 2023). A consistent pattern has been observed in human samples, showing ERα expression in Sertoli cells from childhood through puberty (Valeri et al., 2020). Thus the link between testosterone and aggression and violence is due to these being rewarded with social status. This could explain why some studies find a link between testosterone and pro-social behaviour, if pro-social behaviour is rewarded with social status. Rats who were given anabolic steroids that increase testosterone were also more physically aggressive to provocation as a result of "threat sensitivity". One study found that administering testosterone increased verbal aggression in some participants. The Annals of the New York Academy of Sciences has found that the use of anabolic steroids (which increases testosterone) among teenagers is correlated with increased likelihood of using violence. One study proposed that natural selection may have caused men to be more sensitive to situations in which their status is challenged, and that testosterone is the key factor that causes these situations to spark into aggression.
