Acquired tolerance

Brodeur J, DuBois KP. 1964. Studies on the mechanism of acquired tolerance by 0,0-diethyl S-2 (ethylthio) phosphorodithioate (Di-Syston). Arch Int Pharmacodyn Ther 149 560-570. 

Billingham RE, Brent L, Medawar PB Actively acquired tolerance of foreign cells. Nature 1953 172 603-606. 

In 1952, Rider, Ellinwood, and Coon (7) demonstrated that rats can become tolerant to octamethyl pyrophosphoramide (OMPA). Since then it has been shown that rats can acquire tolerance to a variety of organophosphorus cholinesterase inhibitors. Typical of such reports is that of Bombinski and DuBois (2), who administered 0,0-diethyl S-2-ethyl-2-mercaptoethyl phosphorodithioate (Di-Syston) to rats each day for periods as long as 60 days. Signs of poisoning appeared after 2 days, but began to subside after 7-10 days, even though the activity of brain cholinesterase remained at or about 20% of its normal value from the 5th day onward. 

Because it is possible that free acetylcholine may constitute the predominant fraction of the reduced total which is observed after adaptation has occurred, our experiments do not rule out the possibility that cholinergic receptors may acquire tolerance to acetylcholine, as Brodeur and DuBois suggest. We are not prepared to evaluate the importance of increased resistance to carbachol which they present in support of their hypothesis, in view of the strong nicotinic component of the action of that drug. 

Acquired tolerance is dealt with by increasing the dose. There is no need for an arbitrary maximum dose. 

Chronic use of morphine and other opioids is marked by acquired tolerance to the depressant agonist effects, e.g. analgesic action and respiratory depression (the fatal dose becomes higher), but not to some stimulant agonist effects, e.g. constipation and miosis, which persist. 

Acquired tolerance develops over days with continued frequent use and passes off (variably for different actions) over a few days to weeks. 

Acquired tolerance may rapidly reach a high degree, and an addict may take morphine 600 mg (heroin equivalent 400 mg) or even more several times a day. An average addict is more likely to take about 300 mg. Duration of tolerance after cessation of administration is variable for different actions, from a few days to weeks. Thus, addicts who have undergone withdrawal and lost tolerance, and who later resume their opioid careers may overdose themselves inadvertently. 

Liu, J., H. Chen, D.S. Miller, J.E. Saavedra, L.K. Keefer, D.R. Johnson, C.D. Klaassen and M.P. Waalkes. Overexpression of glutathione S-transferase II and multidrug resistance transport proteins is associated with acquired tolerance to inorganic arsenic. Mol. Pharmacol. 60 302-309, 2001. 

Speed of developing acquired tolerance Likehhood of experiencing intoxication as pleasme Metabolism of the drug Psychiatric symptoms Prior experiences/expectations Propensity for risk-taking behavior... 

Acquired tolerance can be divided into three major types pharmacokinetic, pharmacodynamic, and learned tolerance, and includes acute, reverse, and cross-tolerance. 

C Approaches for Acquired Tolerance to Abiotic Stress of Economically Important Crops... 

Key Words Abiotic stress acquired tolerance antioxidant breeding crop plants cross protection functional genomics heat shock heat shock factors heat shock proteins hydrogen peroxide oxidative stress reactive oxygen species signaling pathways stress tolerance transgenic plants. 

Tolerance to abiotic stress has drawn the attention of many scientific disciplines continuously attempting to improve productivity and quality in crop production. This chapter is intended to review current knowledge of abiotic stresses in the agricultural context and to provide some examples of enhancing crop tolerance to such environmental stress. This review does not cover all aspects of scientific literature but emphasizes acquired tolerance in the context of crop production and food quality. 

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