| How Adenosine Prevents Fat Store Utilization Dr. Lawrence Wang, Ph.D. University of Alberta M. Sc. Rice University Ph.D. Cornell University Editor of the North American Journal of Comparative Physiology Access Technology The Effects of the Access Technology on “Cold” The main source of fuel for the muscles is glucose and free fatty acids. Cold temperatures stimulate the muscles to contract to increase body temperature. Being that muscle is only 25 percent efficient, heat is generated as a by-product each and every time a muscle is contracted. Shivering is a good example of our protective mechanisms to keep us warm. In order to keep warm in the cold, supporting aerobic activity becomes critical. This is not only relevant to maintaining cold tolerance but also to sustaining exercise activity in general. Cold-----stimulates----Nervous System----to break down Fat------to Free Fatty Acids-----and----Glycogenolysis---to cause the release---of Glucose from the---Liver and Muscle---to help fuel----the muscles----to sustain---shivering/exercise---to create Heat & Work The Formation of the Fat Guard…Adenosine Adenosine is the protector of the best source of fuel that we have. Fat provides 9cal per gram…carbohydrates and protein provide only 4cal per gram each. Humans are the only mammals that exercise to get rid of fat…most wild animals risk their lives to get fat. Remember, you don’t have to eat fat to get fat…all excess carbohydrates that we eat will be converted to fat because under normal conditions carbohydrates are never eliminated in the urine except in the case of diabetes or kidney disease. Farmers feed their livestock grain when they want to fatten them up! Adenosine is formed as a natural by-product of our own metabolism. The harder we exercise the more adenosine is produced in the cell resulting from the breakdown of Adenosine Tri-phosphate (ATP). Adenosine tri-phosphate is the key energy currency of our body with adenosine being the end product of energy metabolism. Adenosine Triphosphate--- breaks down to Adenosine Diphosphate---broken down to Adenosine Monophosphate---ending up as Adenosine---the end product of energy metabolism. This is the normal cascade flow of energy metabolism. Once adenosine is formed it diffuses out of the cell into the extracellular space (outside the cell) due to the increased concentration gradient. Adenosine may now enter the general circulation in the blood or exert a local effect on the target fat cells, which possess specific adenosine receptors…thus, blocking the conversion of stored fat to free fatty acids that could be used as fuel.” Keep in mind…the harder you exercise or expend energy…the more adenosine that is going to be produced…resulting in more fat cell receptor sites being filled…blocking further release of fat to free fatty acids that could otherwise be used as fuel. This is a natural protective mechanism that prevents us from over utilizing the best source of fuel that we have…Fat! How Adenosine Prevents Fat Store Utilization In the fat cells (white adipose) the conversion of stored fat into usable fat ( fatty acids) requires an enzymatic reaction by Cyclic AMP or cAMP. In other words the more cAMP available the greater utilization of fat. The formation of cAMP is enhanced by a neurochemical transmitter called norepinephrine (NE). Norepinephrine promotes the formation of cAMP from Adenosine Triphosphate (ATP) . Adenosine---the end product of ATP utilization---inhibits the activity of Norepinephrine…that is important for the conversion of fat to free fatty acids. Thus, the action of adenosine is to serve as a negative feedback signal to reduce energy and fat consumption, being most prominent when the rate of ATP utilization is high, as in intense exercise. As energy and fat conservation serves to enhance survival in nature, the role of adenosine is considered to be adaptive, as energy procurement is often difficult and dangerous in nature. The only exception is modern man, who can procure energy at will without the fear of predation, but unfortunately adenosine’s long-standing role in energy and fat conservation is still with us. The Effect ofAdenosine on Muscular Contraction Adenosine also exerts inhibition of the release of Acetylcholine (Ach). This neurotransmitter elicits muscles contraction and adenosine inhibits the release of (Ach) decreasing the intensity and duration of muscle contraction, especially during aerobic exercise. This inhibition of Acetylcholine is another protective mechanism that prevents over-expenditure of the body’s fuel. |
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