Biological effect

There is an abundant literature on the biochemistry of Cd as a toxic element in a variety of organisms from bacteria to humans. Like all other reactive trace metals, Cd can be toxic simply because of unspecific reactions with protein ligands. For example, reaction of Cd with cysteine thiol groups, for which it has a great affinity, can denature enzymes and make them inactive. More specific toxic effects of Cd result from blockage of certain physiological functions when Cd substitutes for other metals, Ca or Zn, in particular. The ionic radius of Cd and Ca are very similar and cadmium can interfere with Ca metabolism or replace Ca in structural functions [30,31]. 

In humans the principal route of exposure to Cd is through tobacco smoke with the net result that smokers have a Cd concentration in blood 4-5 times that of non-smokers [30]. Food is the main secondary source of Cd intake as a result of Cd accumulation in agricultural soils from fertilizers and atmospheric deposition. The Environmental Protection Agency reference dose for Cd in drinking 

The two principal causes of Cd toxicity in humans are skeletal demineralization and renal dysfunction. There is also some evidence that Cd may be a carcinogen (through inhalation exposure) and that it may cause reproductive or developmental health effects [32]. 

Even at a low level of exposure, the replacement of Ca by Cd in bones results in poor mineralization and leads to fragility and risk of bone fracture. Because Cd is a good chemical analog for Zn, Cd can also substitute for Zn in the active center of many Zn-enzymes and block their activity. It seems, for example, that the substitution of Cd for Zn in alkaline phosphatase—an important Zn enzyme in bone formation—may contribute to bone demineralization [31]. 

The itai-itai disease, the most infamous case of Cd toxicity to humans, was first reported in the mid 1940s in the Jinzu River basin in Japan. It was a combination of bone and kidney disease. The disease was particularly painful ( itai-itai translates into ouch ouch ) because of the fragility of the bones which could not sustain any pressure. Prolonged exposure to Cd resulted from ingestion of contaminated rice, as rice fields were being irrigated by river water contaminated with the waste from a zinc mine [34,35]. 

The most well known of the naturally occurring phenethylamine derivatives (Table I) are the transmitters of the sympathetic nervous system, epinephrine, norepinephrine, and dopamine. All these compounds are 3,4-dioxygenated in the aromatic nucleus and are collectively known as the catecholamines. Norepinephrine is the transmitter of most sympathetic postganglionic fibers, dopamine is the predominant transmitter of the mammalian extrapyramidal system and of several mesocortical and mesolimbic neuronal pathways, and epinephrine is the major hormone of the adrenal medulla (363). The literature that has accumulated on the action of these compounds in higher animals is enormous. Metanephrine and normetanephrine are known from animals as deactivated metabolites of epinephrine and norepinephrine that result from the action of the enzyme catechol O-methyltransferase (364). 

The action of tyramine on nerve receptors is mainly indirect by release of norepinephrine and dopamine from neuronal storage sites (363, 384). Tyramine and its /3-oxidized counterpart octopamine have been referred to as false neurotransmitters because these compounds can be taken up, stored, and released from nerve endings in a way similar to those of the principal neurotransmitters norepinephrine and dopamine (385). Octopamine was first discovered in salivary glands of octopods (386). The compound is widely distributed in the animal kingdom and is present in high amounts in the nervous system of several species of invertebrates such as molluscs and arthropods, where it acts as a specific transmitter substance (387). Octopamine may also play a role in the regulation of adrenergic neurotransmission in mammals (387). Administration of octopamine to intact animals produces a transient rise in blood pressure (388). 

Synephrine is a sympathomimetic agent with mainly direct effects on a-adren-ergic receptors. It has been used to treat hypotension and also as an ocular decongestant (389). It occurs in tangerines (Table II) in concentrations high enough to be physiologically active (119). 

Pseudoephedrine and phenylpropanolamine [( )-norephedrine] are sympathomimetic agents with actions similar to those of ephedrine and are most commonly used for the relief of nasal congestion (363). Pseudoephedrine has been stated to have less pressor activity and central nervous system effects than ephedrine. 

Phenylpropanolamine also has been used as an anoretic, and the mechanism of the anoretic effect has been shown to be similar to that of amphetamine (597). 

There are other causes of pain and pulpal irritation. Hydraulic pressure developed during the seating of a restoration can lead to pulpal damage (Hoard et al., 1978). The movement of fluid under osmotic pressure has been dted as a cause of pain (Brannstrom Astrom, 1972). 

If the cement is mixed too thinly it may etch the tooth enamel because of its excess acidity (Docking et ai, 1953 Abramovich, Macchi Ribas, 1976). Of course, etching can promote mechanical attachment to the tooth (Ware, 1971). 

Fluoride is found in some zinc phosphate cements, generally as stannous fluoride. The cements are weaker and have less resistance to dissolution than normal zinc phosphate cements (Myers, Drake Brantley, 1978 Williams et al., 1979). They release fluoride over a long period (de Freitas, 

1973) and this is taken up by enamel (Wei Sierk, 1971). This results in reduced enamel solubility (Gursin 1965 Skibell Shannon, 1973) and increased hardness (Yamano, 1968). Fluoride-releasing cements should reduce the incidence of enamel decalciflcation under orthodontic bands but this effect has not been recorded. 

Although fluoride is added as the tin salt, fluoride release is accompanied by the release of aluminium and not tin (de Freitas, 1973). There is little leaching out of tin apart from an initial wash-out. Of course, aluminium is not released from the normal cement (Wilson, 1976 Wilson, Abel Lewis, 

Promotes cell cycle progression in most cell types 

Fetal development promotes growth and differentiation of fetal cells and organogenesis Promotes longitudinal body growth and increased body weight Promotes enhanced functioning of the male and female reproductive tissue Promotes growth and differentiation of neuronal tissue 

Sea has been estimated to be of the order of 100 million tonnes (GLOBEC, 1993). 

A secondary fluorescence maximum (SFM), almost exclusively caused by Prochlorococcus, is associated with the upper oxic/hypoxic interface (Johnson etal., 1999). This strain of Prochlorococcus, possibly different from the one found in the oligotrophic surface waters, is well-adapted to low light and 02 levels. Similar SFM has also been reported from the ETNP, and is believed to be related to the presence of strong ODZ. 

Chemical and biological processes in the sediments and benthic boundary layer (BBL) are important contributors to oceanic biogeochemical cycles, especially in the Arabian Sea due to its uncommon geographical setting. The oceanographic conditions experienced by various margins (e.g. Somalia/Oman versus India/Pakistan) are widely different, which in conjunction with the extensive mid-depth 02 deficiency produce a variety of BBL and sedimentary environments with respect to, among other factors, food supply, redox status and the nature and activity of benthic communities (Cowie, 2002). 

The suboxic/anoxic conditions prevailing in marginal sediments of the Arabian Sea appear to affect, to a very substantial extent, cycling and global 

In the abyssal region, the onshore-offshore gradients in various parameters of benthic processes generally reflect those in PP and related vertical fluxes of 

Some common examples of enzymes inhibited by phosphate ions include carboxypeptidase, fumarase, urease, phos-phoglucomutase, carboxylase, arylsulphatase and muscle deaminase (for the deamination of adenylic acid). Frequently this inhibition is due to competition of the phosphate with substrates containing phosphate groups or to complex formation with a metal ion essential for the enzyme activity. 

Barbiturate buffers can uncouple oxidative phosphorylation and are also limited by the low solubility of diethyl- 

Although Tris has been a major biochemical buffer for many years, partly because it is relatively inexpensive and 

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For a detailed discussion of the sources and biological effects of doxins see the article Dioxins Not Doomsday in the December 1999 issue of the Journal of Chemical Education pp 1662-1666... 

In experimental animals and in vitro, DHBs show a variety of biological effects including binding of metaboHtes to various proteins. Clastogenic effects have been observed in vitro and in some in vivo studies with the three compounds. No reproductive effects have been shown by conventional studies with either hydroquinone, catechol, or resorcinol (122). Hydroquinone has been shown to induce nephrotoxicity and kidney tumors at very high doses in some strains of rat (123) catechol induces glandular stomach tumors at very high dose (124). Repeated dermal appHcation of resorcinol did not induce cancer formation (125). 

Medical and Biologic Effects of Environmental Pollutants-Manganese, Division of Medical Sciences, National Research Council, National Academy of Sciences, 1973. 

E. C. Foulkes, ed.. Biological Effects of Heavy Metal, Vols. 1—2, CRC Press, Boca Raton, Fla., 1990. 

Microwaves may be used to ionize gases when sufficient power is apphed, but only through the intermediate process of classical acceleration of plasma electrons. The electrons must have energy values exceeding the ioniza tion potential of molecules in the gas (see Plasma technology). Ionizing radiation exhibits more biological-effect potential whatever the power flux levels (2). 

Most, if not all, microwave biological effects and potential medical appHcations are beheved to be the result of heating, ie, thermal effects. The phenomenon of microwave hearing, ie, the hearing of clicking sounds when exposed to an intense radar-like pulse, is generally beheved to be a thermoelastic effect (161). Excellent reviews of the field of microwave bioeffects are available (162,163). 

S. M. Michaelson and J. C. Lin, Biological Effects and Health Implications ofKadiofrequeng Kadiation, Plenum Press, New York, 1987. 

I. K. O Neill and co-workers, eds., N-Nitroso Compounds Occurrence, Biological Effects and Relevance to Human Cancer, International Agency for Research on Cancer, Lyon, Prance, 1984. 

Health Effects Of Exposure to Row Revels oflonifing Radiation, Report of Committee on the Biological Effects of Radiation (BEIR Report V), National... 

Absorption, metaboHsm, and biological activities of organic compounds are influenced by molecular interactions with asymmetric biomolecules. These interactions, which involve hydrophobic, electrostatic, inductive, dipole—dipole, hydrogen bonding, van der Waals forces, steric hindrance, and inclusion complex formation give rise to enantioselective differentiation (1,2). Within a series of similar stmctures, substantial differences in biological effects, molecular mechanism of action, distribution, or metaboHc events may be observed. Eor example, (R)-carvone [6485-40-1] (1) has the odor of spearrnint whereas (5)-carvone [2244-16-8] (2) has the odor of caraway (3,4). 

The natural prostanoids have myriad biological effects and held great promise as potential therapeutic agents in numerous diseases. The natural prostanoids, however, also have three notable drawbacks which medicinal chemists have tried to overcome by molecular modification in order to produce acceptable dmg candidates. These drawbacks are rapid metaboHsm which results in lack of activity if taken orally and a short duration of action, numerous side effects due to their multiplicity of biological activities, and poor chemical stabiUty, a characteristic especially pronounced in PGE, -D, and -I stmctures. 

U.S. radiation protection guidelines are estabHshed by the National CouncH on Radiation Protection and Measurement (NCRP) and are based on the recommendations of the International Commission on Radiological Protection (ICRP). The National Research CouncH also sponsors a report from its advisory committee on the biological effects of ionizing radiations (20). 

Radiation Dosimetry. Radioactive materials cause damage to tissue by the deposition of energy via their radioactive emissions. Thus, when they are internally deposited, all emissions are important. When external, only those emissions that are capable of penetrating the outer layer of skin pose an exposure threat. The biological effects of radiation exposure and dose are generally credited to the formation of free radicals in tissue as a result of the ionization produced (17). 

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