1.
Insulin action in adipose tissue and muscle in hypothyroidism.
Dimitriadis, G, Mitrou, P, Lambadiari, V, Boutati, E, Maratou, E, Panagiotakos, DB, Koukkou, E, Tzanela, M, Thalassinos, N, Raptis, SA
The Journal of clinical endocrinology and metabolism. 2006;(12):4930-7
Abstract
BACKGROUND Although insulin resistance in thyroid hormone excess is well documented, information on insulin action in hypothyroidism is limited. METHODS To investigate this, a meal was given to 11 hypothyroid (HO; aged 45 +/- 3 yr) and 10 euthyroid subjects (EU; aged 42 +/- 4 yr). Blood was withdrawn for 360 min from veins (V) draining the anterior abdominal sc adipose tissue and the forearm and from the radial artery (A). Blood flow (BF) in adipose tissue was measured with 133Xe and in forearm with strain-gauge plethysmography. Tissue glucose uptake was calculated as (A-V)glucose(BF), lipoprotein lipase as (A-V)Triglycerides(BF), and lipolysis as [(V-A)glycerol(BF)]-lipoprotein lipase. RESULTS The HO group had higher glucose and insulin levels than the EU group (P < 0.05). In HO vs. EU after meal ingestion (area under curve 0-360 min): 1) BF (1290 +/- 79 vs. 1579 +/- 106 ml per 100 ml tissue in forearm and 706 +/- 105 vs. 1340 +/- 144 ml per 100 ml tissue in adipose tissue) and glucose uptake (464 +/- 74 vs. 850 +/- 155 micromol per 100 ml tissue in forearm and 208 +/- 42 vs. 406 +/- 47 micromol per 100 ml tissue in adipose tissue) were decreased (P < 0.05), but fractional glucose uptake was similar (28 +/- 6 vs. 33 +/- 6% per minute in forearm and 17 +/- 4 vs. 14 +/- 3% per minute in adipose tissue); 2) suppression of lipolysis by insulin was similar; and 3) plasma triglycerides were elevated (489 +/- 91 vs. 264 +/- 36 nmol/liter.min, P < 0.05), whereas adipose tissue lipoprotein lipase (42 +/- 11 vs. 80 +/- 21 micromol per 100 ml tissue) and triglyceride clearance (45 +/- 10 vs. 109 +/- 21 ml per 100 ml tissue) were decreased in HO (P < 0.05). CONCLUSIONS In hypothyroidism: 1) glucose uptake in muscle and adipose tissue is resistant to insulin; 2) suppression of lipolysis by insulin is not impaired; and 3) hypertriglyceridemia is due to decreased clearance by the adipose tissue.
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Essential amino acids are primarily responsible for the amino acid stimulation of muscle protein anabolism in healthy elderly adults.
Volpi, E, Kobayashi, H, Sheffield-Moore, M, Mittendorfer, B, Wolfe, RR
The American journal of clinical nutrition. 2003;(2):250-8
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Abstract
BACKGROUND Nutritional supplementation may be used to treat muscle loss with aging (sarcopenia). However, if physical activity does not increase, the elderly tend to compensate for the increased energy delivered by the supplements with reduced food intake, which results in a calorie substitution rather than supplementation. Thus, an effective supplement should stimulate muscle anabolism more efficiently than food or common protein supplements. We have shown that balanced amino acids stimulate muscle protein anabolism in the elderly, but it is unknown whether all amino acids are necessary to achieve this effect. OBJECTIVE We assessed whether nonessential amino acids are required in a nutritional supplement to stimulate muscle protein anabolism in the elderly. DESIGN We compared the response of muscle protein metabolism to either 18 g essential amino acids (EAA group: n = 6, age 69 +/- 2 y; +/- SD) or 40 g balanced amino acids (18 g essential amino acids + 22 g nonessential amino acids, BAA group; n = 8, age 71 +/- 2 y) given orally in small boluses every 10 min for 3 h to healthy elderly volunteers. Muscle protein metabolism was measured in the basal state and during amino acid administration via L-[ring-(2)H(5)]phenylalanine infusion, femoral arterial and venous catheterization, and muscle biopsies. RESULTS Phenylalanine net balance (in nmol x min(-1). 100 mL leg volume(-1)) increased from the basal state (P < 0.01), with no differences between groups (BAA: from -16 +/- 5 to 16 +/- 4; EAA: from -18 +/- 5 to 14 +/- 13) because of an increase (P < 0.01) in muscle protein synthesis and no change in breakdown. CONCLUSION Essential amino acids are primarily responsible for the amino acid-induced stimulation of muscle protein anabolism in the elderly.