Hormone action mechanism

The responsiveness of a tissue to a hormone depends on the density of receptors within its component cells. The number of receptors is determined by their rate of synthesis and catabolism, which is itself controlled by complex feedback mechanisms involving hormone action. Some chemicals are known to interfere with this regulation. For example, TCDD can act to increase or decrease the expression of the oestrogen receptor. ... 

Metabolic pathways are regulated by rapid mechanisms affecting the activity of existing enzymes, eg, allosteric and covalent modification (often in response to hormone action) and slow mechanisms affecting the synthesis of enzymes. 

Much of the material on individual endocrine glands present in the twenty-fifth edition has been replaced with new chapters dealing with the diversity of the endocrine system, with molecular mechanisms of hormone action, and with signal transduction. 

Flototto, T. Djahansouzi, S. Glaser, M. Hanstein, B. Niederacher, D. Brumm, C. Beckmann, M. W. Hormones and hormone antagonists mechanisms of action in carcinogenesis of endometrial and breast cancer. Horm. Metab. Res. 2001, 33, 451 -57. 

Hormonal actions on target neurons are classified in terms of cellular mechanisms of action 846... 

Hormonal actions on target neurons are classified in terms of cellular mechanisms of action. Hormones act either via cell-surface or intracellular receptors. Peptide hormones and amino-acid derivatives, such as epinephrine, act on cell-surface receptors that do such things as open ion-channels, cause rapid electrical responses and facilitate exocytosis of hormones or neurotransmitters. Alternatively, they activate second-messenger systems at the cell membrane, such as those involving cAMP, Ca2+/ calmodulin or phosphoinositides (see Chs 20 and 24), which leads to phosphorylation of proteins inside various parts of the target cell (Fig. 52-2A). Steroid hormones and thyroid hormone, on the other hand, act on intracellular receptors in cell nuclei to regulate gene expression and protein synthesis (Fig. 52-2B). Steroid hormones can also affect cell-surface events via receptors at or near the cell surface. 

The molecular details of the mechanism of hormonal action do not always clarify the numerous unknowns of the way in which the intensity of the hormone response is regulated from cell to cell and from minute to minute. There are numerous factors implicated in this process directed at achieving the greatest functional equilibrium of the organism. From the entry of the hormones into the cell to the conclusion of hormonal action, an ensemble of factors arises that intervenes in the process in a decisive way. 

These findings complete the panorama relative to the mechanisms of hormonal action mediated by nuclear receptors. Thus, gene activation mediated by nuclear receptors can respond to three clearly differentiated modalities (1) receptor bound to hormone and not phosphorylated, (2) receptor bound to hormone and phosphorylated, and (3) receptor not bound to hormone and phosphorylated (Filardo 2002 Lee et al. 2002 Powles 2002). 

Structure and physiology of the kidney glomerular filtration tubular activity selective reabsorption and secretion, often using specific carrier mechanisms carbonic anhydrase and acid-base balance. The kidney also produces, and is sensitive to, hormones actions of the hormones ADH, aldosterone and PTH the kidney as a secretory organ erythropoietin, the renin-angiotensin system vitamin D3. 

Metabolism is tightly regulated by a number of mechanisms feedback inhibition, compartmentalization, covalent modification of enzymes (e.g., phosphorylation), and hormone action, among others. 

An additional mode of estrogen and progesterone action is classified as nongenomic effects. Nongenomic mechanisms for steroid hormone action are attributed to responses to estrogens and progestins that occur in a very short time (seconds to several minutes) such that they are difficult to explain by transcriptional activa-... 

P. M. Conn (1984). Molecular mechanism of gonadotropin releasing hormone action. In G. Litwack (Ed.). Biochemical Action of Hormones, vol. 11. New York Academic Press, pp. 67-92. 

Carter-Su C, Schwartz J, Smit LS Molecular mechanism of growth hormone action. Annu Rev Physiol 1996 58 187. 

FIGURE 23-4 Two general mechanisms of hormone action. The peptide and amine hormones are faster acting than steroid and thyroid hormones. 

Mammals are hardly unique in possessing hormonal signaling systems. Insects and nematode worms have highly developed systems for hormonal regulation, with fundamental mechanisms similar to those in mammals. Plants, too, use hormonal signals to coordinate the activities of their various tissues (Chapter 12). The study of hormone action is not as advanced in plants as in animals, but we do know that some mechanisms are shared. To illustrate the structural diversity and range of action of mammalian hormones, we consider representative examples of each major class listed in Table 23-1. 

Possible mechanisms of hormone action, (a) The hormone (H) theoretically activates an enzyme (E) directly as an allosteric effector. (b) Alternatively, a separate binding protein for the hormone, called a receptor (R), may then activate an enzyme, (c) Another possibility interposes an acceptor protein (A) between the receptor and the enzyme. Each interaction is reversible. 

Sutherland, E. W., Studies on the mechanism of hormone action. Science 177 401, 1972. Nobel laureate speech related to discovery of cAMP as second messenger. 

Harvey CB, Williams GR. Mechanism of thyroid hormone action. Thyroid. 2002 12 441-446. 

The purpose of this chapter is to review the basic aspects of endocrine function, including the primary hormones and their effects. The factors regulating hormonal release and the cellular mechanisms of hormone action are also briefly discussed. Finally, the basic ways in which drugs can be used to alter endocrine function are presented. This overview is intend-... 

Advances in our knowledge about molecular mechanisms involved in gene regulation have made a major contribution to ideas about nuclear events in steroid hormone action. Multiple regulatory units in the DNA upstream of the mRNA initiation site exist and complex interactions occur between these units which may contribute to the specificity of steroid hormone action (Ref. 12 and see below). One... 

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