Fasting metabolic responses

Rodgers, J.T. and Puigserver, P. (2007) Fasting-dependent glucose and lipid metabolic response through hepatic... 

Poor response to an adequate dose, raising doubts about unusual pharmacokinetics, such as excessively slow or fast metabolism, leading to unusually low or high blood levels... 

For example, a test dose may identify a fast metabolizer, who may require a higher dose there is no evidence, however, that this approach could accelerate response, an issue that needs to be tested in controlled trials. Further, only limited evidence exists that high doses will shorten the lag period for any psychotropic agent (e.g., divalproex sodium loading dose strategy). 

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. 

Acetylcholine receptors (AChRs) are of two types muscarinic (mAChR) and nicotinic (nAChR) based on the agonist activities of the natural alkaloids, muscarine and nicotine, respectively. These receptors are functionally different. The muscarinic type being G-protein coupled receptors mediate a slow metabolic response via second messenger cascades, while the nicotinic type are ligand-gated ion channels, which mediate a fast synaptic transmission of the neurotransmitter. Skeletal muscles are enriched with nAChRs and are devoid of mAChRs. 

Smith, C. M., Narrow, C. M., Kendrick, Z. V, and Steffan, C. (1987). The effect of pantothenate deficiency in mice on their metabolic response to fast and exercise. Alc/fflwfKrn 36, 115-121. 

Withdrawal of most, or all, caloric intake has been used to treat certain cases of obesity. Such withdrawal provokes many metabolic responses. The body attempts to conserve protein at the expense of other sources of energy, such as fat. The blood glucose concentration decreases by as much as ISmg/dL (1 mmol/L) within the first 3 days of the start of a fast in spite of the body s attempts to maintain glucose production. Insulin secretion is greatly reduced, whereas glucagon secretion may double in an attempt to maintain normal glucose concentration. Lipolysis and hepatic keto-... 

Clinically, this has been shown to make a difference in a small study in males, involving 10 Chinese and 9 Caucasian subjects the Chinese metabolized propranolol more rapidly, clearance was 76% higher, with a lower area under the curve (AUC) and plasma levels lower than that in the Caucasians at all time points. In this study, when dosage was adjusted upwards to equilibrate to Caucasian therapeutic blood levels, a greater response was noted in the Chinese subjects (lower blood pressure and pulse rate) (Zhou et al., 1990). Conversely, the presence of very fast metabolizers in a population may also vary. 

One patient with mania and diabetes developed hyperglycaemia, in the presence of a constant insulin dose, when his serum lithium levels were high (approximately 1.4mmol/L), but reducing the lithium level to 1.1 mmol/L led to a lowering of the fasting blood glucose. However, a study in 6 patients, with type 2 diabetes controlled by diet alone, found that lithium, taken for one week did not alter the metabolic response to a standard 50 g carbohydrate breakfast. ... 

Rhoades, R. A., and Ryder, D. A., 1981, Fetal lung metabolism response to maternal fasting, Biochim. Biophys. Acta 633 621-629. 

Mashego, M.R., van Gulik, W.M. et al (2009) Fast dynamic response of the fermentative metabolism of Escherichia coli to aerobic and anaerobic glucose pulses. Biotechnol. Bioeng, 104 (6), 1153-1161. 

Metabolic acidosis is caused by the release into the bloodstream of excessive amounts of lactic acid and other acidic byproducts of metabolism. These acids enter the bloodstream, react with hydrogen carbonate ion to produce H2CX)5, and shift the ratio HC03 /H2C03 to a lower value. Heavy exercise, diabetes, and fasting can all produce metabolic acidosis. The normal response of the body is to increase the rate of breathing to eliminate some of the CO,. Thus, we pant heavily when running uphill. 

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