Metabolic rate accelerator

The functions of the thyroid hormones and thus of iodine are control of energy transductions. These hormones increase oxygen consumption and basal metabolic rate by accelerating reactions in nearly ail cells of the body. A part of this effect is utlribuicd lo increase in activity of many enzymes. Additionally, protein synthesis is affected by the thyroid hormones. 

Chlorophenols block adenosine triphosphate (ATP) production, without blocking the electron transport chain. They inhibit oxidative phosphorylation, which increases basal metabolic rate and increases body temperature. As body temperature rises, heat-dissipating mechanisms are overcome and metabolism is accelerated. Adenosine diphosphate (ADP) and other substrates accumulate, and stimulate the electron transport chain further. This process demands more oxygen in a futile effort to produce ATP. Oxygen demand quickly surpasses oxygen supply and energy reserves of the body become depleted. 

The presence of excessive THs in the thyrotoxic state induces significant changes in the neuromuscular system. THs cause a predominantly catabolic state, resulting in increased muscle breakdown, wasting and weakness due to an accelerated metabolic rate. There is often an increase in efflux of branched-chain amino acids, phenylalanine and tyrosine from muscle bed, with a net muscle loss. THs also cause an increase in the activity of uncoupled ATPase and sarcoplasmic reticulum vesicles. This increase is much more in the red muscle types than in white ones, which is... 

Owing to the ready availability of narcotine its effects on the animal organism have been studied extensively, but the observations have not indicated any extensive use in medicine. It is effective neither as a prophylactic nor as a curative in malaria (240). It has only a mild narcotic action (241, 242, 243), and as an analgesic it is much weaker than morphine (244, 245), although it has been recorded that it potentiates the activity of morphine four- to sevenfold (246). The cramps due to the action of cocaine are also augmented by the simultaneous use of narcotine. It does not lower the basal metabolic rate appreciably (247), nor does it shorten the induction period in nitrous oxide narcosis (248). Its effect on respiration is one of acceleration (249, 250), and its effect on smooth muscle of the intestine (251-254), of the bladder (255), of the gall bladder (251, 252, 256, 257), and of the uterus (251, 252, 258-261) is depressive, while the amplitude of the peristaltic pulses is increased (262-265). 

Fever elevates the blood GSH index (17-20). The degree of temperature elevation and the duration of hyperpyrexia cannot be correlated with the level of the GSH concentration. The mechanism underlying this effect of fever is not known the coincident elevated metabolic rate is not responsible because experimental hjrperthyroidism in animals lowers the blood GSH index (21-25). Stress in a general sense is perhaps a factor since electric and insulin shock therapies both raise the index after 2 to 6 hr., as do injections of epinephrine and insulin following a similar time interval (26-29). However, ACTH injections in normal man may cause no change or may lower the GSH concentration (30-38). The elevating effect of fever might simply be related to accelerated protein catabolism. 

Another factor to consider is environmental temperature. If it falls below body temperature, heat conserving mechanisms kick in (i.e. cutaneous vasoconstriction and shivering). This causes the metaboUc rate to rise. When environmental temperature increases to a point where it is high enough to raise body temperature, metabolic enzyme action accelerates. Therefore metabolic rate rises with an increase in body temperature. 

While enzymes, like organic catalysts, speed the approach to chemical equilibrium by providing an alternative pathway having a lower energy of activation, they can be distinguished by their enormous capabilities for stereospecific recognition and for rate acceleration. These faculties provide for the brisk conduct of the myriad chemical reactions, termed intermediary metabolism, that form the fabric of life s processes. 

The sensitivity of cellular constituents to environmental extremes places another constraint on the reactions of metabolism. The rate at which cellular reactions proceed is a very important factor in maintenance of the living state. However, the common ways chemists accelerate reactions are not available to cells the temperature cannot be raised, acid or base cannot be added, the pressure cannot be elevated, and concentrations cannot be dramatically increased. Instead, biomolecular catalysts mediate cellular reactions. These catalysts, called enzymes, accelerate the reaction rates many orders of magnitude and, by selecting the substances undergoing reaction, determine the specific reaction taking place. Virtually every metabolic reaction is served by an enzyme whose sole biological purpose is to catalyze its specific reaction (Figure 1.19). 

The various chemical mechanisms of enzyme action will not be discussed here but an overview of enzyme kinetics is essential to allow a full understanding of metabolic control. Enzymes accelerate biochemical reactions. The precise rate of reaction is influenced by a number of physiological (cellular) factors ... 

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