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INNOVATIVE METHODOLOGY

A comparison of ²H₂O and phenylalanine flooding dose to investigate muscle protein synthesis with acute exercise in rats

¹Department of Health and Kinesiology, Texas A & M University, College Station, Texas; and ²Department of Nutrition, Case Western Reserve University School of Medicine, Cleveland, Ohio

Submitted 28 October 2008 ; accepted in final form 10 April 2009

The primary objective of this investigation was to determine whether ²H₂O and phenylalanine (Phe) flooding dose methods yield comparable fractional rates of protein synthesis (FSR) in skeletal muscle following a single bout of high-intensity resistance exercise (RE). Sprague-Dawley rats were assigned by body mass to either 4-h control (CON 4 h; n = 6), 4-h resistance exercise (RE 4 h; n = 6), 24-h control (CON 24 h; n = 6), or 24-h resistance exercise (RE 24 h; n = 6). The RE groups were operantly conditioned to engage in a single bout of high-intensity, "squat-like" RE. All rats were given an intraperitoneal injection of 99.9% ²H₂O and provided 4.0% ²H₂O drinking water for either 24 (n = 12) or 4 h (n = 12) prior to receiving a flooding dose of L-[2,3,4,5,6-³H]Phe 16 h post-RE. Neither method detected an effect of RE on FSR in the mixed gastrocnemius, plantaris, or soleus muscle. Aside from the qualitative similarities between methods, the 4-h ²H₂O FSR measurements, when expressed in percent per hour, were quantitatively greater than the 24-h ²H₂O and Phe flooding in all muscles (P < 0.001), and the 24-h ²H₂O was greater than the Phe flooding dose in the mixed gastrocnemius and plantaris (P < 0.05). In contrast, the actual percentage of newly synthesized protein was significantly higher in the 24- vs. 4-h ²H₂O and Phe flooding dose groups (P < 0.001). These results suggest that the methodologies provide "qualitatively" similar results when a perturbation such as RE is studied. However, due to potential quantitative differences between methods, the experimental question should determine what approach should be used.

fractional rates of protein synthesis; skeletal muscle