Action of hormones

Prior to isolation of insulin, patients were treated by diet, consisting largely of boiled vegetables to control the glycosuria and presumably the blood glucose level (Allen, 1919). However, patients simply faded away and probably died from effects of loss of muscle protein (Chapter 16). About 2000 years ago diabetes was aptly described  

The action of a hormone is, first, binding to a receptor to form a hormone-receptor complex. The binding is reversible (i.e. equilibrium binding) as with other receptors. 

Second, the complex stimulates an effector system which 

For a cell surface receptor, the binding of the hormone must change the activity of an effector system that results in a change in concentration of an intracellular messenger. This is achieved by location of the effector system on the cytosolic side of the membrane, although the receptor and effector system may be combined in one complex. 

Only if the hormone is lipid soluble, and can therefore transfer rapidly across the cell membrane, can the receptor be within the cell. Examples of such hormones include the steroid hormones (e.g. sex hormones, adrenal steroids and dihydroxycholecalciferol) and thyroxine (i.e. triiodothyronine). 

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Smooth muscle contractions are subject to the actions of hormones and related agents. As shown in Figure 17.32, binding of the hormone epinephrine to smooth muscle receptors activates an intracellular adenylyl cyclase reaction that produces cyclic AMP (cAMP). The cAMP serves to activate a protein kinase that phosphorylates the myosin light chain kinase. The phosphorylated MLCK has a lower affinity for the Ca -calmodulin complex and thus is physiologically inactive. Reversal of this inactivation occurs via myosin light chain kinase phosphatase. 

The mechanisms by which the growth supplements in serum-free medium act are still not understood. In order to achieve an understanding of the biochemical basis for the hormonal and growth factor requirements of animal cells, the basic mechanism of action of hormones and growth factors must be determined. The biochemical basis for the nutritional requirements of animal cells can only be determined when we have an understanding of the metabolism of the different types of animal cells. 

Figure 15-8. Mechanisms of control of an enzyme-catalyzed reaction. Circled numbers indicate possible sites of action of hormones. .Alteration of membrane permeability conversion of an inactive to an active enzyme, usually in-...

Section V deals with aspects of extracellular and intracellular communication. Topics covered include membrane structure and function, the molecular bases of the actions of hormones, and the key field of signal transduction. 

The importance of pathways and networks was revealed by the study of the mechanisms of action of hormones, as well as by numerous studies on the mechanisms of oncogenesis and development. Biology articles and books... 

The glycerol produced by the action of hormone-sensitive lipase in the adipose tissue cannot be utilized by adipose tissue itself. Adipose cells lack the enzyme glycerol kinase, which is necessary to convert glycerol to glycerol phosphate. 

Figure 14.10 Diagrammatic representation of regulation of the opening of an ion channel by phosphoiylation of a protein in the channel. The neurotransmitter-receptor complex functions as a nucleotide exchange factor to activate a G-protein which then activates a protein kinase. This is identical to control of G-proteins in the action of hormones (Chapter 12, see Figure 12.21). Phosphorylation of a protein in the ion channel opens it to allow movement of Na+ ions. The formation of the complex, activation of the G-protein and the kinase takes place on the postsynaptic membrane. An example of the structural organisation and the involvement of a G-protein is shown in Chapter 12 (Figure 12.6).

Certain tissues of the female reproductive tract, which are subject to the trophic action of hormones, exhibit a high frequency of neoplasia. Cancer of the breast, the second most common form of cancer in American women, and the rarer endometrial cancer in women, are often responsive to treatments with estrogens or progestins. The toxicity of these hormonal treatments compared with standard cancer chemotherapy is low. 

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. 

The cytokines are a large and heterogeneous group of proteins with diverse functions. Some are immunoregulatory proteins synthesized within lymphoreticular cells and play numerous interacting roles in the function of the immune system and in the control of hematopoiesis. The cytokines that have been clearly identified are summarized in Table 55-2. In most instances, cytokines mediate their effects through receptors on relevant target cells and appear to act in a manner similar to the mechanism of action of hormones. In other instances, cytokines may have antiproliferative, antimicrobial, and antitumor effects. 

Which one of the following is characteristic of low insulin levels A. Increased glycogen synthesis B. Decreased gluconeogenesis from lactate C. Decreased glycogenolysis D. Increased formation of 3-hydroxybutyrate E. Decreased action of hormone-sensitive lipase Correct answer = D. 3-hydroxybutyrate—a ketone body—synthesis is enhanced in the liver by taw insulin levels, which favor activation of hormone-sensitive lipase and release of fatty acids from adipose tissue. Glycogen synthesis is decreased, whereas gluconeogenesis is increased. 

You have learned about many types of complex formation between small molecules and proteins in biochemistry class. The action of hormones... 

Rivera R, Yacobson I, Grimes D. The mechanism of action of hormonal contraceptives and intrauterine contraceptive devices. Am J Obstet Gynecol. 

Henderson, I.W. and Chester Jones, I. (1974). Actions of hormones on osmoregulatory systems of fish. Fortschritte derZoologie, 391-418. 

Toxicants that disturb the action of hormones involved in reproduction and development are of particular ecotoxicological significance. Endocrine disrupters may bind to hormone receptor sites, thus interfering with the essential functions of the endocrine system. Endocrine disrupters may... 

The major source of free fatty acids in the blood is from the breakdown of triacylglycerol stores in adipose tissue which is regulated by the action of hormone-sensitive triacylglycerol lipase (see Topic K4). Fatty acid breakdown and fatty acid synthesis are coordinately controlled so as to prevent a futile cycle (see Topic K3). 

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