Hormone-like substances

Microorganisms at the rhizosphere are known to produce plant growth regulators using precursors released by the roots (71), which can influence root morphology (3) the degradation of these hormone-like substances could be prevented by their incorporation into humic molecules, which would preserve their chemical properties. However, definite proof is still lacking recent studies have shown the... 

Woolley and Shaw24 have recently put forth an interesting and worthy hypothesis that schizophrenia may be due to interference with the functioning of serotonin in the brain. This newly discovered hormone-like substance may be an important key. The evidence on which the hypothesis is based is that various chemically related substances (antagonists), notably lysergic acid diethylamide, produce, when given to well individuals, conditions which in some cases closely resemble schizophrenia. 

The animal organism contains more than 100 hormones and hormone-like substances, which can be classified either according to their structure or according to their function. In chemical terms, most hormones are amino add derivatives, peptides or proteins, or steroids. Hormones regulate the following processes ... 

Can we say anything more precise about the function of gibberellins in flower formation Most plant biologists feel that flower formation is controlled by specific, hormone-like substances, so-called flower hormones. Attempts at ex-... 

The thyroid is a part of the endocrine system. The endocrine system monitors and manufactures or synthesizes many hormones and hormone-like substances. For this reason, the endocrine system and its sub-systems have many built in "checks and balances" to assure proper substance ratio or synergy. It is no surprise that thyroid functions are no exception. 

Pheromone. A hormone-like substance that acts as an attractant. 

PG [Prostaglandin] A group of hormone-like substances found in virtually all tissues and organs that are derived from unsaturated fatty acids. These substances mediate a wide range of physiological functions, the most common of which are muscular constriction and the mediation of inflammation. Letters after PG in the abbreviation symbolize different substitutions made to the hydrocarbon backbone, whereas subscript numbers indicate tlae degree of unsaturation (i.e., the number of double bonds). 

A man s musculature is affected by several hormones and hormone-like substances. Some have anabolic (meaning to add) effects upon muscle tissue while being catabolic (meaning to subtract) to adipose (fat) tissue. Others are anabolic toward adipose tissue while having a muscle wasting effect. Still others alter the activity of different hormones by mediating hormonal effects. It is the ratio of one hormone to the others that we refer to as a hormone profile. 

PROSTAGLANDINS A group of potent hormone-like substances that are produced in various tissues of the hody. Prostaglandins help with a wide range of physiological functions, such as control of hlood pressure, contraction of smooth muscles, and modulation of inflammation. 

Hormones released from the endocrine glands and those secreted by the organs other than the classical endocrine glands as well as their main functions are listed in Table 7.2. It should be borne in mind that numerous hormones and hormone-like substances might not have been mentioned in Table 7.2. 

Not only the biosynthesis of these hormone-like substances but also that one of the major groups of the well-known plant hormones is, as already mentioned, strongly connected to typical secondary plant metabolism. 

Arachidonic (all ds 5,8,11,14-eicosatetraenoic) acid has been shown to have equivalent or even greater activity than linoleic add, and linolenic (all d59,12,15-octadecadienoic) acid is about 1.5 times as effective as linoleic acid. Mammals cannot synthesise fatty acids with double bonds closer than carbon atom 9 from the terminal methyl group. Such acids have to be supplied in the diet. Linoleic add (18 2n-6) and a-linolenic acid (18 3 n-3) are thus dietary essentials. Arachidonic acid is synthesised in the body from linoleic acid. However, one of the steps in the synthesis, a A-6 desaturation, is rate-limiting and production may be slow and an exogenous supply advantageous (see Box 3.1). Linoleic and a-linolenic acids are referred to as the essential fatty acids (ERA). Like other polyunsaturated acids, they form part of various membranes and play a part in hpid transport and certain lipoprotein enzymes. In addition, they are the source materials for the synthesis of the eicosanoids. These include the prostaglandins, thromboxanes and leukotrienes, hormone-like substances that regulate... 

There are many indications for the existence of such hormone-like substances. They can dominate the phenomenon of correlation of various parts and of regulations, which are so evident in the course of life of the higher plant. The investigations in this field are most difficult, since the formation of these substances is not well-localised and channels like those of blood and lymph are lacking in plants. 

In seedlings the cotyledons are remarkable for the extent and speed of the growth of roots and leaves in the dark. Therefore Went assumed that the hormone-like substances (rhizocaline, phyllocaline) other than auxin... 

Since hormones are substances elaborated by the cells of one tissue (endocrine tissue) to act on and control the function of cells of another tissue (target tissue) which are distant from the endocrine tissue, it seems necessary to distinguish them from those substances now classified as paracrines, chalones, and neurotransmitters. These latter compounds are hormone-like substances which are also elaborated by one tissue and which also act on different adjacent tissues. The principal difference between hormones and paracrines, chalones, and neurotransmitters is that the former have a circulating form while the latter do not. However, in many cases, neurotransmitter substances are found in nonnervous tissues where they appear to act as hormones, and thus the distinction between hormones and the other classes of signal molecules is not always sharp. 

---