Answer to the question- Amino acids in the post absorptive state ..

During a medical rotation, a medical student volunteered for a respiratory physiology exam that determines basal metabolic rate and the respiratory quotient. She followed the protocol for a resting individual in the post absorptive state. Which of the following amino acids would be found in the highest concentration in serum?

A. Alanine and Glutamine

B. Arginine and Ornithine

C. Glutamate and Aspartate

D. Branched chain amino acids

E. Hydrophobic amino acids

Answer- A- Alanine and Glutamine.

Post absorptive state is the state of the body 3-5 hours after meals.

It is that period of time in the body during which cell metabolism is primarily fueled by nutrients stored from previous meals; this state is dominated by glucagon release from the alpha cells of the pancreatic islets in response to hypoglycemia; various “insulin antagonists,” thyroid hormones (T3 and T4), glucocorticoids (cortisone, cortisol, hydrocortisone) from the adrenal cortex, epinephrine from the adrenal medulla, and human growth hormone from the anterior pituitary are also present in increased amounts and contribute to the physiological processes which occur in this state.

Primarily, hepatocytes are the responsive targets to glucagon and, in response to glucagon arrival, release glucose into the plasma to be used by nervous tissue in oxidative pathways to generate ATP.

The liver obtains this glucose in two ways:

(1) by releasing glucose which had been stored as glycogen (glycogenolysis) and

(2) by synthesizing new glucose molecules from the breakdown products of lipid and protein catabolism (gluconeogenesis)

Most other tissues shift to energy production from lipid and protein catabolism. Adipocytes liberate fats (triglycerides) into the bloodstream (lipolysis) to support the metabolism of these other tissues, the glycerol  released from triglycerides is used to synthesize glucose (gluconeogenesis); the liver oxidizes free fatty acids for fuel, producing ketone bodies (ketogenesis) as by-products (figure)

Nervous tissue is not responsive to glucagon, but continues to utilize the glucose.

Post absorptive state

Figure- Changes occurring  in the post absorptive state

In the post absorptive state, the muscles release alanine and glutamine which are found in highest concentration. Most of the alanine is removed by liver (glucose- alanine cycle) and glutamine is taken up by kidney. The carbon skeleton of alanine is used for glucose production whereas amino group is removed in the form of ammonia which is detoxified forming urea.

In the kidney glutamine is hydrolyzed by glutaminase enzyme forming ammonia and glutamate. Ammonia is converted to ammonium ion and contributes to acid secretion by the kidney. Renal glutaminase activity is increased in conditions of acidosis to promote acid secretion whereas in conditions of alkalosis the glutaminase activity is decreased to enhance acid retention in the body.

The other set of amino acids are not increased in serum more than alanine and glutamine in the post absorptive state. Since the amino acids are not available at that time through diet in the post absorptive and the body cannot synthesize them, the essential amino acids  such as branched chain amino acids or arginine cannot be in higher concentration. Aspartate and glutamate are mainly used for transamination reactions, mediating transfer of amino group from one amino acid to another, so they are never in high concentration in serum themselves under physiological conditions.

Thus the only option is A- Alanine and Glutamine.

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