Exogenous substances

Monoamine Oxidase Inhibitors. MAOIs inactivate the enzyme MAO, which is responsible for the oxidative deamination of a variety of endogenous and exogenous substances. Among the endogenous substances are the neurotransmitters, norepinephrine, dopamine, and serotonin. The prototype MAOI is iproniazid [54-92-2] (25), originally tested as an antitubercular dmg and a close chemical relative of the effective antitubercular, isoniazid [54-85-3] (26). Tubercular patients exhibited mood elevation, although no reHef of their tuberculosis, following chronic administration of iproniazid. In... 

An endocrine disrupter is an exogenous substance that causes adverse health ejfects in an intact organism, or its progeny, subseguent to changes in endocrine function. ... 

The term opioid refers to any exogenous substance that acts as an agonist at any of several receptors. Opioid antagonists are drugs that bind to a receptor but produce no actions. The poppy plant, Papaver somniferum, from which opium is obtained, is grown in many areas of the world. Morphine constitutes 10% of opium, and codeine can be obtained direcdy from opium. Semisynthetic opioids such as heroin and oxycodone are obtained directly or indirectly from morphine. There are other distinct chemical classes of drugs with opioid actions, including the methadones. 

Pharmacokinetics—The science of quantitatively predicting the fate (disposition) of an exogenous substance in an organism. Utilizing computational techniques, it provides the means of studying the absorption, distribution, metabolism and excretion of chemicals by the body. 

Physiologically Based Pharmacodynamic (PBPD) Model—A type of physiologically-based dose-response model which quantitatively describes the relationship between target tissue dose and toxic end points. These models advance the importance of physiologically based models in that they clearly describe the biological effect (response) produced by the system following exposure to an exogenous substance. 

The uronic acid pathway is the source of glucuronic acid for conjugation of many endogenous and exogenous substances before excretion as glucuronides in urine and bile. 

Levels of a number of metabolites as well as a number of enzymes in body fluids are indicative of disease conditions. Many of the enzymatic reactions mentioned above have been used in solution clinical assays as well as in test strips.446,497-508 512-515 Assays for hydrogen peroxide and the enzyme peroxidase using NADH and a tetrazolium salt have been de-scribed.509,5io Assays of exogenous substances (e.g., drugs or their metabolites) also utilize this chemistry. The determination of alcohol using alcohol dehydrogenase is an example.511 As mentioned above, the assay of enzyme levels can also be achieved using tetrazolium salts.516-520... 

Lymphocytes are of two sizes smaller lymphocytes, with a diameter of 6-8 pm, and larger lymphocytes, with a diameter up to 18 pm. They are found not only in blood, but in lymph and in every tissue of the body. Larger lymphocytes are believed to be cells that differentiate into T and B lymphocytes when activated by specific antigens. The life span of lymphocytes may vary from a few days to many years. Lymphocytes have been suggested as potential carriers for transporting macromolecules, particularly DNA, to other cells. Low molecular weight exogenous substances can be introduced into lymphocytes by electrical breakdown methods. 

Although the measurement of GFR with inulin is quite accurate, it is inconvenient because it requires the continuous infusion of this exogenous substance for several hours. More often, in clinical situations, the plasma clearance of creatinine is used to estimate GFR. Creatinine, an end-product of muscle metabolism, is released into the blood at a fairly constant rate. Consequently, only a single blood sample and a 24-h urine collection are needed. Measurement of the plasma clearance of creatinine provides only an estimate of GFR in fact, this measurement slightly overestimates it. A small amount of creatinine is secreted into the urine (about 10% on average). In other words, the concentration of creatinine in the urine is the result of the amount filtered (as determined by GFR) plus the amount secreted. 

It is ironic that possibly the first animal model of relevance to immunotoxicology was reported by Portier and Richet in 1902 [45] in an attempt to induce tolerance to a sea anemone toxin, they accidentally produced a shock reaction in dogs. Since this was not the protective effect they had hoped to produce (phylaxis for protection in Greek), they named the reaction anaphylaxis [46], The irony, of course, is that this serious reaction, mediated by IgE in humans, has proven to be notoriously difficult to predict based on animal studies. This is no trivial issue, since anaphylaxis is a serious, life-threatening reaction associated with exposure to drugs, foods, cosmetic ingredients, and other exogenous substances [47],... 

One of the most important functions of GSTs is the detoxification of endogenous as well as exogenous substances via conjugation with glutathione... 

Active transport mechanisms exist to remove exogenous substances from gastrointestinal epithelial cells (efflux mechanisms) thereby limiting entry into the systemic circulation. It is not possible to identify, which substances could be removed by efflux mechanisms from physicochemical data. 

Various techniques have been proposed and developed over the years for the examination of fetuses for potential teratogenic effects of exogenous substances such as pharmaceutical candidates (1-8). Each method has its advantages and disadvantages (see below). For regulatory testing purposes (9, 10), a balance between rapidity and thoroughness is paramount. Microdissection meets this requirement. 

Know how to inactivate a harmful exogenous substance (chapter 9). 

An agonist is a substance that interacts with a specific cellular constituent, the receptor, and elicits an observable biological response. An agonist may be an endogenous physiological substance such as a neurotransmitter or hormone, or it can be an exogenous substance such as a synthetic drug. 

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