In hyperpolarized [1-13C]pyruvate MRI of the brain, pyruvate-to-bicarbonate conversion, representing oxidative metabolism, is detected at low levels, despite the highly oxidative metabolism of the brain. We sought to determine the effect of lactate excitation on bicarbonate detection in healthy rats imaged in a cross-over fashion (lactate flip angle = 90° or 0°). In the brain, the bicarbonate signal-to-noise ratio increased 65 % when lactate was not excited. This effect was not observed in the heart, kidneys or liver. Collectively, our data show that lactate saturation limits bicarbonate detection in the brain solely, which has implications for study designs.