Hormones interaction

Responses to various hormones can cross-talk by means of multiple interactions/modifications. One example has already been discussed Phosphorylase b kinase is responsive both to cAMP and to Ca2+ ions. Receptors can themselves be phosphorylated by protein 

Multiple hormones may affect a single target tissue simultaneously. Therefore, the response of the target tissue depends not only on the effects of each hormone individually, but also on the nature of the interaction of the hormones at the tissue. The three types of hormone interactions include  

In permissiveness, one hormone enhances the responsiveness of the target tissue to a second hormone in other words, the first hormone increases the activity of the second. For example, the normal maturation of the reproductive system requires reproductive hormones from the hypothalamus, pituitary, and gonads as well as the presence of thyroid hormone. Although thyroid hormone by itself has no effect on the reproductive system, if it is absent the development of this system is delayed. Therefore, thyroid hormone is considered to have a permissive effect on the reproductive hormones, facilitating their actions causing sexual maturation. 

When the actions of one hormone oppose the effects of another, the result is antagonism. For example, insulin decreases blood glucose and promotes the formation of fat. Glucagon, on the other hand, increases blood glucose and promotes the degradation of fat. Therefore, the effects of insulin and glucagon are antagonistic. 

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M. Muller. C. Deigele, and H. Ziegler, Hormonal interactions in the rhizosphere of maize (Zea mays L.) and their effects on plant development. Z. Pflanzenernahr. Bodenk. 152 241 (1989). 

Like steroid hormones, thyroid hormones interact with receptors to alter genomic activity and affect the synthesis of specific proteins during development [25-28], As with testosterone and progesterone, metabolic transformation of thyroxine (T4) is critical to its action [25-28]. Moreover, as with steroid hormones, thyroid hormones alter brain functions in adult life in ways that both resemble and differ from their action during development [25-28]. 

Developmentally, thyroid hormones interact with sex hormones such that hypothyroidism prolongs the critical period for testosterone-induced defeminization (see below) [3] in contrast, the hyperthyroid state prematurely terminates the sensitivity to testosterone [3]. Undoubtedly, an important link in these and other effects is synapse formation. Hypothyroidism increases synaptic density, at least transiently [3]. Interesting parallels with synapse formation are reported for learning behavior in rats neonatal hypothyroidism impairs learning ability, whereas hyperthyroidism accelerates learning initially, followed by a decline later in life [3]. 

PXR in Adrenal Steroid Homeostasis and Drug-Hormone Interactions... 

A challenge posed to researchers was therefore to account for diverse physiological effects emanating from the same receptor/hormone interaction. Structurally, the insulin receptor (IR) is a tetrameric protein, composed of two smaller extracellular a units and two larger transmembrane [3 units (see Figure 4.20a). 

The hormone interacts with its receptor by equilibrium binding. The dissociation constant is kJh. 

The physiology of penile erection involves an interplay of anatomical, hemodynamic, neurophysiological, and sex hormone interaction. Penile erection is the result of a complex interaction between the central nervous system and other local factors. This physical event also can be influenced by psychological factors. 

With the help of co-immimoprecipitation it could be shown that the receptors of steroid hormones interact with at least three chaperones, Hsp90, Hsp70 and Hsp56 (fig. 4.10). The term Hsp (Heat shock protein) is derived from the observation that these proteins were produced at higher levels following heat treatment. Furthermore, one finds a 23 kDa acidic protein in the apo-receptor complex whose fimction is not yet clear. 

The hormonal interactions controlling bone mineral homeostasis. In the body (A), l,25(OH)2D is produced by the kidney under the... 

Many biological processes depend on a specific interaction between molecules. The interaction often involves a macromolecule (protein or nucleic acid) and a smaller molecule, a ligand. Specific examples include enzyme-substrate interactions and receptor protein-hormone interactions. One of the most... 

Farach-Carson MC, Davis PJ. Steroid hormone interactions with target cells cross talk between membrane and nuclear pathways. J Pharmacol Exp Ther. 2003 307 839-845. 

Nuclear Hormone Receptors. Certain hormones interact directly with hormonal receptors that are located on the chromatin within the cell nucleus (see Fig. 28-2).3 Thyroid hormones (T3 and T4) are a primary example of hormones that bind directly to nuclear receptors.29 After binding, thyroid hormones invoke a series of changes similar to those caused by the steroid-cytosolic receptor complex that is, the nucleus begins to transcribe messenger RNA, which is ultimately translated into specific proteins. In the case of the thyroid hormones, these new proteins usually alter the cell s metabolism. Thyroid hormones are discussed in more detail in Chapter 31. 

PTH works with two other primary hormones— calcitonin and vitamin D—in regulating calcium homeostasis. These three hormones, as well as several other endocrine factors, are all involved in controlling calcium levels for various physiologic needs. How these hormones interact in controlling normal bone formation and resorption is of particular interest to rehabilitation specialists. Regulation of bone mineral homeostasis and the principal hormones involved in this process are presented in the following section. 

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