Selective attenuation of signal from flowing hyperpolarized 13C spins can be used to enhance the fraction of signal from locally-produced metabolites. Here, we look at the effect of flow attenuation in the rat kidney on pyruvate metabolite ratios using an interleaved pulse-acquire/spin-echo+bipolar gradient acquisition scheme. With flow-sensitizing gradients applied, lactate- and alanine-to-pyruvate ratios increase as anticipated. Unexpectedly, the ratio of the hydrate and keto forms of pyruvate increases as well, suggesting a greater fraction of flowing keto-pyruvate. The increasing lactate signal fraction after saturation indicates that labelled circulating lactate becomes predominant over the course of the acquisition.