Part of the book: Glucocorticoids
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
The hydromineral homeostasis is fundamental to survival due to maintenance constant the osmotic properties of the plasma and proper tissue perfusion pressure, being maintained primarily through the regulation of the ingestion and urinary excretion of water and electrolytes, mainly sodium. The Renin-Angiotensin System (RAS) plays an essential role in the maintenance of hydromineral homeostasis by eliciting sodium and water intake and by inducing sodium urinary retention through aldosterone release and hemodynamic effect via angiotensin II a key component of the RAS. The hypothalamus-pituitary system also plays a fundamental role in the maintenance of body fluid homeostasis by secreting vasopressin (AVP) and oxytocin (OT) in response to osmotic and non-osmotic, and volemic stimuli. Furthermore, some studies report that besides reproductive function and sexual behavior, ovarian gonadal hormones, mainly 17β-estradiol (E2), modulate other non-reproductive functions such as cardiovascular system, body fluid balance, mood, mental state, memory, and cognition. Estradiol is known to mediate hydromineral homeostasis and blood pressure mainly by attenuating RAS actions. On the other hand, estradiol modulates neurohypophysial hormones secretion in many different ways. In this chapter, we will discuss the main non-reproductive effects of E2 on the control of hydromineral homeostasis, focusing on ingestive behavior and neurohypophyseal hormonal release.
Part of the book: Reproductive Hormones