Physiologic dependence

Since alcohol dehydrogenase is required for the conversion of retinol to retinal, excessive and prolonged ethanol ingestion can impair the physiological function of vitamin A. The decreased conversion of retinol to retinal results from competitive use of the enzyme by ethanol. Night blindness may result, since the visual cycle is a retinol-dependent physiological process. 

The first fraction of the previous equation shows that An is exclusively determined by the effective permeability Peff of drug since all other variables are species-dependent physiological parameters. In terms of characteristic times, the An of a drug can also be defined as the ratio of the mean small intestinal transit time (Tsi), to its absorption time R/Peff. 

Camus 1, Davies P.E., Spicer JI, Jones M.B. (2004) Temperature-dependent physiological response of Carcinus maenas exposed to copper. Marine Environmental Research 58 781-785. 

As mentioned earlier, understanding the pH equation and the regulation and control of pH is fundamentally important when considering very many life and health processes. A simple indication of the importance of environmental pH is for growth of crops (soil pH) and acid rain (water pH), which can affect the ecosystem. Indeed, optimum conditions for purification of water and sewage treatment also are pH dependent. Physiologically, pH is critical to maintain normal body functions and key to biochemical reactions in the blood and other body fluids. Buffers and buffer systems are the primary means to regulate and maintain pH, and are discussed in more detail below (with examples in Appendix 3). 

These polymers were selected owing to their ability to promptly transit from hydrated coil to dehydrated globule conformation when temperature increases above their lower critical solution temperature (LCST). Homopolymers of NIPAM have a LCST in aqueous media around 32°C, which is not compatible with physiological conditions. Thus, to be exploitable for in vivo drug delivery, this temperature must be increased by copolymerization with other hydrophilic monomers. When these monomers have ioniz-able moieties such as methacrylic acid (MAA, pKa=5.4), the increase in LCST is dependent on ionization, and therefore the polymers acquire pH-dependent physiological solubility (2). 

Four ways that neurohormones and neurohormone-dependent physiological processes might be affected are ... 

Low-molecular-weight RSNOs have been identified in a variety of organ systems (Table II) and are believed to play important roles in NO-dependent physiological responses, particularly in the vasculature. S-Nitroso-L-cysteine... 

The rates of synthesis of the neurotransmitters serotonin, acetylcholine, and probably also norepinephrine depend physiologically on the availability to the brain of their precursor molecules, the nutrients tryptophan, choline, and tyrosine, respectively. The brain concentration of each precursor can rapidly be influenced by the diet food ingestion thus readily modifies the synthesis of each of these neurotransmitters in brain. Brain neurons that utilise serotonin, acetylcholine, or norepinephrine are involved in neuronal networks that control a number of body functions and behaviours for example, appetite, food choice, sleep, memory, and mood). Thus dietary constituents are able normally to affect these functions and, when given as large doses of pure nutrients, to serve as treatments for brain diseases involving monoaminergic or cholinergic neurons. 

Ouatas T, Le MS, Demeneix BA et al (1998) T3-dependent physiological regulation of transcription in the Xenopus tadpole brain studied by polyethylenimine based in vivo gene transfer. Int J Dev Biol 42 1159-1164... 

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