Hormone interaction definition

An important observation linking Ca + to hormone action involved the definition of the intracellular targets of Ca action. The discovery of a Ca -dependent regulator of phosphodiesterase activity provided the basis for a broad understanding of how Ca and cAMP interact within cells. 

Many aspects relating to the specificity and intensity of gene transcription in response to hormones remain open. Nevertheless, a prudent conclusion permits establishing that two definite elements are intervening the interaction of the receptor dimer with the palindrome and several protein-protein interactions that are produced between the dimer and the remaining components of the transcription machinery (Beato 1989). 

Less well-defined but particularly important in terms of the function of non-neuronal cells are so-called receptor-operated channels [6,7]. By definition these are channels in the plasma membrane which open in response to hormone-receptor interaction without a change in membrane potential. The mechanism of their opening may either be by a direct coupling of receptor (possibly via a G protein) with the channel, or by an indirect coupling via the generation of an intracellular messenger such as cAMP or the putative messenger, inositol 1,3,4,5-tetrakisphosphate. 

All enzymes are in fact labeled, at least by their active binding ate for substrates, and by coenzymes (catalytic sites) which both together enable them to fulfil their very specific catalytic function. The same can be said about hormones and antibodies which are adapted for a specific interaction with a target cell or antigen by some definite mode of labeling. 

It proved difficult to definitively demonstrate CRH synthesis from immune cells, although numerous studies provided evidence this does happen (Aird et al., 1993 Ekman et al., 1993). Eventually it became clear that regulation of CRH synthesis and release in immune cells differs from that in hypothalamic neurons. While immune cells may synthesize and release much smaller concentrations of CRH and other neuroimmune peptides, and although their release may require de novo synthesis, an inherently slow process, the fact that immune cells release these hormones locally in the target area compensates for both of these factors to some extent. These data indicating site and tissue specific effects of CRH, sometimes even contradictory effects, point to the complex interrelationship betw een the nervous, endocrine and immune systems, an interaction that has yet to be deciphered completely. 

Prevot V, Croix D, Bouret S, Dutoit S, Tramu G, et al. 1999. Definitive evidence for the existence of morphological plasticity in the external zone of the median eminence during the rat estrous cycle Implication of neuro-glio-endothelial interactions in gonadotropin-releasing hormone release. Neuroscience 94 809-819. 

The areas discussed in this chapter - the discovery of new oligosaccharins, their structural elucidation, the description of their physiological effects and interactions with known plant hormones, the investigation of their biosynthesis, transport, binding, action and turnover within the plant, and the definition of their biological importance - are all open books in this novel and rapidly advancing field of plant science. 

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