Measurement of the rate of myofibrillar protein degradation using the arteriovenous difference in plasma 3-methylhistidine concentration of rats.
(58/199)
There are several methods for measuring the rate of myofibrillar protein degradation using 3-methylhistidine (3-MeHis) levels in urine, plasma and isolated muscle. However, these methods lack the accuracy of rate measurements. Therefore, it is necessary to develop a new method for determining the rate of myofibrillar protein degradation. We characterized an arteriovenous difference method using 3-MeHis plasma concentration. Rats were fasted overnight and subsequently administered leucine (135 mg/100 g BW) or fed a 20% casein diet. The rate of myofibrillar protein degradation was calculated by multiplying the femoral artery blood flow rate by the arteriovenous difference in 3-MeHis concentrations (vein-artery). The blood was collected from the femoral vein and abdominal aorta. The release of 3-MeHis from hindlimb muscle was significantly suppressed (p<0.05) in rats fed leucine or the 20% casein diet, indicating that myofibrillar protein degradation was suppressed. These results suggest that the evaluation of the rate of myofibrillar protein degradation using the arteriovenous difference method reflects nutritional conditions in a more physiological manner. (+info)
Effects of feeding hexane-extracts of a shochu distillery by-product on skeletal muscle protein degradation in broiler chicken.
(59/199)
We have found that shochu distillery by-product (SDBP) contains a growth promoting factor that can be extracted with ether. In the present study, we administered hexane-extracts of SDBP (HSDBP) to broiler chickens and observed changes in skeletal muscle protein degradation in order to clarify the mechanism of growth promotion due to SDBP feeding. The pectoralis superficial muscle weight was significantly increased by HSDBP feeding. Plasma N(tau)-methylhistidine concentration was significantly decreased by HSDBP, showing that the rate of muscle protein degradation decreased. It was also found that the expression of mRNA of ubiquitin-proteasome system and calpain was decreased by HSDBP. These results indicate that growth promotion due to SDBP is caused by suppression of skeletal muscle protein degradation, which is related to the ubiquitin-ptoteasome system and calpain. (+info)
Vitamin A deficiency increases protein catabolism and induces urea cycle enzymes in rats.
(60/199)
A role for intracellular histamine in collagen-induced platelet aggregation.
(63/199)
We previously demonstrated that newly formed intracellular histamine mediates platelet aggregation in response to phorbol-12-myristate-13-acetate (PMA). We now report further investigations of the role of histamine during physiological activation of platelets by collagen. Platelets stirred with collagen produced histamine; the rise in histamine precedes the onset of aggregation. The dose response for collagen stimulation of histamine synthesis and platelet aggregation is similar. Inhibitors of histidine decarboxylase (HDC) block both aggregation and histamine synthesis in parallel. Histamine production is not dependent on aggregation; both the intracellular histamine receptor antagonist, N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine-HCl (DPPE), and the cyclooxygenase inhibitors, aspirin and indomethacin, inhibit collagen-induced aggregation but not histamine synthesis. DPPE also inhibits collagen-induced serotonin secretion and thromboxane production. The effects of DPPE and HDC inhibitors are significantly reversed by the addition of histamine (0.1 to 10 mumol/L) to saponin-permeabilized platelets, though histamine alone has no pro-aggregatory effects. The results suggest that newly synthesized intracellular histamine has a role in collagen-induced platelet activation and that it may act to promote the generation of thromboxane and the secretion responses of platelet granules. (+info)
What rate of infusion of intravenous nutrition solution is required to stimulate uptake of amino acids by peripheral tissues in depleted patients?
(64/199)
We examined the effect of varying the quantities (0, 0.1, 0.2, 0.3, and 0.4 gN.kg-1.[day]-1) of nitrogen input on N balance, 3-methylhistidine (3MH) excretion, plasma amino acid concentration and the net flux of amino acids across the leg in depleted patients requiring parenteral nutrition. The calorie-to-nitrogen ratio was 140 to 1 (kcal:1 gN) and consequently the patients received varying amounts of calories (8, 14, 28, 42, and 56 kcal.kg-1.[day]-10. There was negative nitrogen balance and net loss of amino acids from the limb during fasting. An infusion of 0.2 gN.kg-1.[day]-1 of IVN reversed the net catabolic process and resulted in equilibrium of peripheral total amino acid flux and of tyrosine flux without a decrease in 3MH excretion. Net uptake of total amino acids and tyrosine in peripheral tissues was achieved with 0.4 gN.kg-1.[day]-1 and 56 kcal.kg-1.[day]-1. This was associated with a fivefold increase in 3MH excretion (p less than 0.01), indicating that net anabolism occurred with increased protein turnover. Fifty per cent of the amino acids taken up by peripheral tissues during infusions of 0.4 gN.kg-1.[day]-1 was due to the uptake of glutamate (Glu) and 20% was due to the uptake of branched chain amino acids (BCAA). Plasma Glu concentration, [Glu], did not increase with increasing IVN infusion, but BCAA concentrations did. Although the mean plasma [Glu] did not change with IVN infusion, there was an independent effect of plasma [Glu] (p less than 0.0001) and of N input (p less than 0.0001) on Glu flux, indicating that even at high infusion rates the maximal capacity of peripheral tissues to take up Glu had not been reached. (+info)