Fasting, metabolic adaptation

Gonzalez, A. A., Kumar, R., Mulligan, J. D., Davis, A. J., Weindruch, R., and Saupe, K. W. 2004. Metabolic adaptations to fasting and chronic caloric restriction in heart, muscle, and liver do not include changes in AMPK activity. Am. J. Physiol. Endocrinol. Metab. 287 E1032-E1037. Grassi, G. 2004. Leptin, sympathetic nervous system, and baroreflex function. Curr. Hypertens. Rep. 6 236-240. 

Among the difficulties caused by prolonged fasting are metabolic disorders caused by vitamin deficiencies. What vitamins are needed during starvation to ensure that cells can continue to carry out the metabolic adaptations discussed in Section 30.3.1 of the text ... 

Interdependence of AMPK and SIRTl for metabolic adaptation to fasting and exercise in skeletal muscle. Cell Metab 11 213-219... 

While an individual s phenotype can directly assess a clinical measureable biologic function of interest (e.g., whether an individual is a fast or slow metabolizer of a certain drug), phenotyping is often expensive and not readily adapted for routine clinical practice. Analysis of genetic information—genotyping—might prove to be more efficient and better able to be adapted to the individualization of drug therapy. 

When food intake decreases, the utilization of fat and protein reserves in the body enables various essential metabolic processes to continue during the nutritional inadequacy. In the early stage of fasting or starvation, glucose requirements of the brain and nervous system are fulfilled by mobilization of glycogen in the liver. This short-term adaptation lasts only a day until glycogen stores are exhausted. Gluconeogenesis... 

One interpretation of the above results is that the Wistar rat has a better ability to adapt to a Mn-deficient diet than does the Sprague-Dawley. Thus we hypothesized that this differential response to Mn deficiency between the strains would allow us to better identify metabolic responses to the consumption of Mn-deficient diets. In our initial study, weanling Sprague-Dawley and Wistar rats were fed diets containing either 45 or 1 ug Mn/g for 6 weeks. After this period, the rats were fasted overnight and then jLijtubated with 1 g of the 1 ug Mn/g diet which was labeled with Mn. The diet was given as a 50% slurry made with deionized water. Six hours after intubation the animals were killed and tissues were collected and counted. 

The slow phase of the stress system is characterized by processes that promote recovery from, and adaptation to, the stressful conditions that prompted the response. At the level of the hypothalamus, this phase is probably mediated by the urocortins acting through CRHR2 receptors (Reul and Holsboer, 2002 de Kloet et al., 2005). In contrast to the fast phase, the slow phase is associated w ith activation of the parasympathetic nervous system, w hich promotes the appetitive and metabolic functions, w hich help to restore homeostasis. As cortisol levels... 

Lactate produced by smooth muscle of swine carotid artery has been shown to be quantitatively derived from extracellular glucose, whereas gly-cogenolysis provides carbohydrates for oxidative metabolism (Lynch and Paul, 1983, 1987). Interestingly, the lactate dehydrogenase (LDH) isoenzyme pattern varies between slow (aorta) and fast (portal vein and bladder) smooth muscle in rat, such that aorta has a higher proportion of the H subunit, which has a higher affinity for lactate and is product-inhibited at lower concentrations of lactate (Malmqvistef flZ., 1991). Thus the slow aortic muscle is more adapted for oxidative metabolism than the faster bladder and portal vein muscles. 

EXAMPLE 13.21 Type II muscle fibers are subdivided into type Ila and type Ilb. Type Ila can use both aerobic and anaerobic metabolism to produce ATP whereas type lib fibers use only anaerobic metabolism. In contrast to type I muscle fibers, type lib fibers contract rapidly after stimulation by a nerve impulse. They have evolved for short-lived, powerful contractions by the possession of characteristically active myosin ATPases and a dense packing of contractile filaments. So much of the cytoplasmic space is taken up with filaments that little exists for mitochondria. Similarly, these fibers are associated with a relatively poor blood supply. Type lib fibers are also known as white and fast-twitch muscle fibers and are adapted for short-lived but powerful contractions. The relative paucity of mitochondria and the poor blood supply impose obvious constraints on the generation of ATP during exercise. 

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