Effects of 3-hydroxybutyrate on the hypoxic and reoxygenated atria from fed and fasted rats.

When exposed to hypoxia, the isolated atria from fed rats released lactate into the medium and underwent a decline of the peak developed tension and pacemaker frequency. The atria from 24-h fasted rats showed a rise in the resting tension together with a greater decline of the pacemaker rate and a lower lactate output than those from fed rats. The exposure to 5 mM 3-hydroxybutyrate caused only a small and brief decline in the pacemaker rate in the fed rats atria indicating that ketone bodies are able to exert only a minor detrimental effect on the hypoxic atria. Since the lactate output remained unaffected, this effect cannot be ascribed to a lowering in the energy supply from anaerobic glycolysis. On the contrary, 3-hydroxybutyrate improved the post-hypoxic recovery of the peak tension in the atria from fasted rats. This finding may be reflecting an anaplerotic role of 3-hydroxybutyrate, thus suggesting that in addition to glucose a second substrate is needed to meet the energy demand in the reoxygenated atria from fasted rats.