Cortisol physiological effects

Figure 12.11 The cortisol pyramid. On the basis of the biochemical and physiological effects, the function of the hormone is the chronic maintenance of the blood glucose and glutamine levels. FFA - long-chain fatty acids.

The biochemical and physiological effects of cortisol are snmmarised in Figure 12.10. Higher than normal concentrations of cortisol improve mood and reduce the activity of the immune system. Hence, they are routinely used to reduce chronic inflammation. There are, however, side-effects of these high levels increased levels of blood glucose, obesity and retention of water giving rise to moon face . 

An account of the principles which help to understand how hormones achieve their roles in the body is given in Chapter 12. The understanding is based on separation of the effects of hormones into three components the action, the effects (biochemical and physiological) and the function. A steroid hormone binds to a cytosolic intracellular receptor, which then moves into the nucleus where it binds to DNA at a specific site (the steroid response element) and activates genes which result in the formation of proteins that elicit biochemical and physiological effects. This is discussed for cortisol in Chapter 12 and aldosterone in Chapter 22. Much of the interest in the reproductive steroid hormones is in the physiological effects and how these account for their functions. 

In addition to behavior changes, exposure to the alarm odor also has physiological effects. For instance, in pearl dace, Semotilus margarita, the levels of plasma cortisol and glucose increase 15 minutes after the alarm and are back to normal after 5 hours. The brain concentrations of dopamine, norepinephrine, 5-hydroxytryptamine, or tryptophan did not change (Rehnberg et al., 1987). The fish recovered physiologically much sooner than the behavioral activation For example. Von Frisch (1941) observed that minnows avoided the site of their encounter with alarm substance for many hours, even days. 

Transcortin acts as a reservoir from which a constant supply of unbound cortisol may be provided to target cells. In addition, when serum albumin levels are low, less circulating cortisol becomes bound, which yields a greater physiological effect. Not only does protein binding control the amount of biologically active cortisol available, but it also reduces the rate at which steroids are cleared from the blood and thus limits steroid suppression of corticotrophin release from the pituitary gland. 

The primary glucocorticoid released in humans is cortisol (also known as hydrocortisone). Cortisol synthesis and secretion are under the control of specific hypothalamic and pituitary hormones.7,24 31 Corticotropinreleasing hormone (CRH) from the hypothalamus stimulates the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary. ACTH travels in the systemic circulation to reach the adrenal cortex, where it stimulates cortisol synthesis. Cortisol then travels in the bloodstream to various target tissues to exert a number of physiologic effects (see Physiologic Effects of Glucocorticoids, later). 

These receptors are chiefly responsible for the physiological effects of steroid hormones such as cortisol as well as thyroid hormone and vitamin A. They are proteins that share a common basic structure consisting of a ligand binding domain and a DNA binding domain (comprised of zinc finger motifs). They operate as ligand-responsive transcription factors (see Chap. 17 for further discussion). 

Figure 12.10 The effects of cortisol. These can be divided into two classes, (i) Physiological levels of cortisol result in changes that maintain the blood glucose level, (ii) Higher levels (pharmacological doses) have an anti-inflammatory effect and a central effect on wellbeing. It is the breakdown of protein that provides amino acids, which along with glucose are used to synthesise glutamine (Chapter 8).

Most attempts of using hormones as psychotropic medications were conducted with gonadal or with thyroid hormones, mainly because of the apparent mood changes associated with physiological or disorder-associated changes in levels or activity of these hormones. However, as shown in Table 17-1, current applications are broader and involve several hormones and systems. It is anticipated that, with acquired knowledge on mood effects of several other hormones, that list will continue to expand. Here, I focus on psychotropic effects of gonadal and thyroid hormones. Cortisol and melatonin are only briefly discussed. 

Mancera, J.M., Perez-Figares, J.M. and Femandez-Llebrez, P. (1994). Effect of cortisol on brackish water adaptation in the euryhaline gilthead seabream (Sparus aurata L.). Comparative Biochemistry and Physiology 107A, 397-402. 

Ogawa, M. (1975). The effects of prolactin, cortisol and calcium-free environment of water influx in isolated gills of Japanese eel, Anguilla japonica. Comparative Biochemistry and Physiology 52A, 539-543. 

Umminger, B.L. and Gist, D.H. (1973). Effects of thermal acclimation on physiological responses to handling stress, cortisol and aldosterone injections in the goldfish, Carassius auratus. Comparative Biochemistry and Physiology 44A, 967-977. 

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