The hypothalamic-pituitary-adrenal axis and the female reproductive system

The hypothalamic-pituitary-adrenal (HPA) axis and the female reproductive system are intertwined and exhibit a complex relationship. Thus, the HPA axis exerts profound, mostly inhibitory effects, on the reproductive axis, with corticotropin-releasing hormone (CRH) and CRH-induced propiomelanocortin peptides inhibiting hypothalamic GnRH secretion, and with glucocorticoids inhibiting pituitary LH and ovarian estrogen and progesterone secretion and rendering estrogen-target tissues, such as the endometrium, resistant to the gonadal steroid. These effects of the HPA axis are responsible for the "hypothalamic" amenorrhea of stress, depression and eating disorders, and the hypogonadism of Cushing's syndrome. Conversely, estrogen directly stimulates the CRH gene, which may explain the slight hypercortisolism of females and the preponderance of depressive, anxiety, and eating disorders, as well as Cushing's disease in women. Interestingly, several components of the HPA axis and their receptors are present in reproductive tissues, as autocoid regulators of their various functions. These include ovarian and endometrial CRH, which may participate in the inflammatory processes of the ovary, that is, ovulation and luteolysis, and of the endometrium, that is, implantation and menstruation. Finally, the hypercortisolism of the latter half of pregnancy can be explained by high levels of placenta CRH in plasma. This hypercortisolism causes a transient adrenal suppression in the postpartum period, which may explain the postpartum blues/depression and autoimmune phenomena of this period.