Endogeneous body substances

Viral infections continue to be significant causes of morbidity and mortality and at the same time continue to be resistant to treatment by small molecules. Avridine (6) is an antiviral compound which has shown some activity in a variety of animal tests apparently based upon its ability to stimulate a number of cells to produce the high molecular weight endogenous antiviral substance interferon. Thus, the compound is believed to operate indirectly by stimulating the body s own natural defenses against viral penetration into host cells. Avridine is synthesized by... 

Organic anion transporters play important roles in the elimination of a variety of endogenous anionic substances, xenobiotics, and their metabolites from the body... 

Peptide transmitters Many peptides have been identified in the CNS, and some meet most or all of the criteria for acceptance as neurotransmitters. The best-defined ones are the opioid peptides (beta-endorphin, met- and leu-enkephalin, and dynorphin), which are distributed at all levels of the neuraxis. Some of the important therapeutic actions of opioid analgesics (eg, morphine) are mediated by receptors for these endogenous peptides. Substance P is localized in type C neurons involved in nociceptive sensory pathways in the spinal cord. Peptide transmitters differ from nonpeptide transmitters in that (1) the peptides are synthesized in the cell body and transported to the nerve ending via axonal transport, and (2) no reuptake or specific enzyme mechanisms have been identified for terminating their actions. 

Furthermore, a carcinogenic effect is observed in the case of overproduction of various own-body enzymes. Tumor induction through own-body substances is referred to as induction by endogenous factors. 

CONCLUSION. The importance of coenzyme Q as a catalyst for respiration imparts status as an essential metabolite. It may have other significant roles. For man and other higher animals a simple precursor substance with an aromatic ring may have vitaminlike status, but dietary ubiquinone seems, on the whole, to be unimportant unless it provides the aromatic nucleus for endogenous (body) synthesis. 

Endogenous substances such as serotonin, amino acids, purines, and pyrimidines all have biological activity and are tolerated in the human body. Therefore, these can be used in some cases as starting points for synthetic drugs. For example, the amino acid tryptophan and neurotransmitter... 

PLC studies in the field of medicine cover the processes of separation, purification, and determination of xenobiotics or endogenous substances present in body fluids and tissues. Such research is carried out with the following aims ... 

In addition to the passive diffusional processes over lipid membranes or between cells, substances can be transferred through the lipid phase of biological membranes through specialized systems, i.e., active transport and facilitated diffusion. Until recently, the active transport component has been discussed only for nutrients or endogenous substances (e.g., amino acids, sugars, bile acids, small peptides), and seemed not to play any major role in the absorption of pharmaceuticals. However, sufficient evidence has now been gathered to recognize the involvement of transporters in the disposition of pharmaceuticals in the body [50, 127]. 

Other substances that can accumulate within the body include poorly soluble particulates that are deposited in the alveolar region of the lungs, substances that bind irreversibly to endogenous proteins, and certain metals and ions that interact with the crystal matrix of bone. The properties of these substances are such that the body cannot readily remove them hence they gradually build up with successive exposures and the body burden can be maintained for long periods of time. 

The chemical transmitters may be small molecules— notably acetylcholine, norepinephrine, epinephrine, serotonin, dopamine, or histamine. Acetylcholine and norpeinephrine are the dominant neurotransmitters in the parasympathetic and sympathetic nervous systems, respectively. Dopamine and serotonin are employed primarily in the central nervous system. Neurotransmitters may also be more complex peptides (small proteins) such as substance P, vasopressin, endorphins, and enkephalins. The latter agents are of particular importance to our considerations of opium since they represent the endogenous opiates—agents that exist within the body whose actions are mimicked by exogenous, or outside, agents such as morphine, heroin, codeine, and so on. These neurotransmitters serve to convey information between neurons across the synaptic cleft (the junction where two neurons meet) or at the neuroeffector junction (the site between neuron and an innervated organ such as muscle or secretory gland). 

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