All living organisms have evolved by developing concomitant physiological and behavioral adaptations to environment. Through these processes, biological rhythms, such as reproduction, can be synchronized by environmental cues, which include not only the light/dark cycle itself but also the feeding pattern. These adaptations depend on two highly conserved and interrelated systems: an endogenous timing system and the hypothalamic-pituitary-adrenal (HPA) axis. In mammals, the biological circadian rhythms are controlled by a “master oscillator,” the suprachiasmatic nucleus of the hypothalamus (SCN). Through neural signals to paraventricular nucleus of hypothalamus (PVN), the SCN also modulates the activation of the HPA axis, ultimately resulting in the circadian rhythm of glucocorticoid secretion by the adrenal cortex. Glucocorticoids, in turn, are well known for their important role in the regulation of energy homeostasis. Accordingly, obese animals exhibit increased glucocorticoid levels and are more susceptible to glucocorticoid-induced anabolic effects. In parallel, glucocorticoids modulate reproductive function and fertility: at physiological levels, glucocorticoids control the timing of puberty onset and gonadal steroidogenesis, as well modulate the immune system, which determines conception and pregnancy progression. However, stress-induced glucocorticoid secretion may exert a dual effect on reproductive function.
Part of the book: Corticosteroids