During a fasting period, a little epinephrine (adrenaline) is released into circulation from our adrenal glands (see Figure 4.3 and Table 4.5). Among epinephrine’s many roles will be its influence upon the liver and skeletal muscle. It will support the effects of glucagon in the liver that were just mentioned. In skeletal muscle, the slightly elevated epinephrine will lightly promote the breakdown of glycogen to glucose. Contrary to the glucose produced from the breakdown of liver glycogen, this glucose is not released into the blood. Rather, this glucose becomes a supportive energy source for those muscle cells while fat is the major energy source. However, when this glucose is used for energy in those cells, a little bit of lactate may be produced. This lactate can enter circulation, reach the liver, and be converted to glucose. This glucose can then be released into the blood. Therefore, our skeletal muscle can modestly contribute to maintaining our blood glucose concentration during fasting.
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