The effects of hypoxia on the pacemaker activity of the isolated atria from fed and fasted rats.

When exposed to hypoxia, the spontaneously beating isolated atria from 24 h fasted rats exhibited a greater decline of their contraction frequency than those from fed rats. Furthermore, in a significant number of the fasted atria, hypoxia led to a complete cessation of pacemaker activity. Addition of insulin improved the performance of fed atria but was ineffective in the fasted atria. Lactate output, both in the presence or absence of added insulin was greater in the atria from fed rats. The extent of glycogen breakdown was similar in both groups of atria. It is suggested that these effects of fasting on pacemaker activity might at least partly have resulted from an inhibition of the glucose utilization under hypoxic conditions. Since fasted atria use faster their endogenous triglycerides, the present observations support the notion that fatty acids are detrimental to the heart during oxygen restriction.