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This Article Full Text Full Text (PDF) All Versions of this Article: 294/3/E551    most recent 00467.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Zhang, X.-j. Articles by Wolfe, R. R. PubMed PubMed Citation Articles by Zhang, X.-j. Articles by Wolfe, R. R.

Acute responses of muscle protein metabolism to reduced blood flow reflect metabolic priorities for homeostasis

¹Metabolism Unit, Shriners Hospital for Children and ²Department of Surgery, The University of Texas Medical Branch, Galveston, Texas

Submitted 19 July 2007 ; accepted in final form 12 December 2007

The present experiment was designed to measure the synthetic and breakdown rates of muscle protein in the hindlimb of rabbits with or without clamping the femoral artery. L-[ring-¹³C₆]phenylalanine was infused as a tracer for measurement of muscle protein kinetics by means of an arteriovenous model, tracer incorporation, and tracee release methods. The ultrasonic flowmeter, dye dilution, and microsphere methods were used to determine the flow rates in the femoral artery, in the leg, and in muscle capillary, respectively. The femoral artery flow accounted for 65% of leg flow. A 50% reduction in the femoral artery flow reduced leg flow by 28% and nutritive flow by 26%, which did not change protein synthetic or breakdown rate in leg muscle. Full clamp of the femoral artery reduced leg flow by 42% and nutritive flow by 59%, which decreased (P < 0.05) both the fractional synthetic rate from 0.19 ± 0.05 to 0.14 ± 0.03%/day and fractional breakdown rate from 0.28 ± 0.07 to 0.23 ± 0.09%/day of muscle protein. Neither the partial nor full clamp reduced (P = 0.27–0.39) the intracellular phenylalanine concentration or net protein balance in leg muscle. We conclude that the flow threshold to cause a fall of protein turnover rate in leg muscle was a reduction of 30–40% of the leg flow. The acute responses of muscle protein kinetics to the reductions in blood flow reflected the metabolic priorities to maintain muscle homeostasis. These findings cannot be extrapolated to more chronic conditions without experimental validation.

stable isotope; gas chromatograph-mass spectrometer; arteriovenous balance; fractional synthetic rate; fractional breakdown rate