Synchronous fluctuations of blood insulin and lactate concentrations in humans

Oscillatory organization is a universal mode of signal transduction in livi ng organisms. In vitro studies suggest spontaneous pulsatile fluctuations o f intracellular energy metabolism. It is possible that, in vivo, some of th ese processes are synchronized by the pulsatile release of insulin. We asse ssed a potential coupling among plasma insulin, glucose, and lactate concen trations, by frequent blood sampling for 24 h in 11 healthy volunteers. Ins ulin sensitivity was assessed using the euglycemic hyperinsulinemic clamp t echnique. Lactate concentrations exhibited pulsatile fluctuations at an ave rage interval of 84 +/- 11 min, whereas sodium and pH were nonpulsatile. Th e lactate concentration pulses closely corresponded to insulin oscillations , which occurred with a periodicity of 86 +/- 11 min. Blood glucose also fl uctuated during daytime at an interval of 89 +/- 32 min. During nighttime, the frequency and amplitude of glucose oscillations were lower. The daytime profiles showed significant temporal coupling and pattern synchrony among insulin, lactate, and glucose. Only the close temporal relationship between insulin and lactate release persisted during nighttime. The temporal coupl ing and pattern synchrony between insulin and lactate were correlated inver sely with insulin sensitivity, and positively with the degree of abdominal obesity. Our results suggest that: 1) the concentration of lactate, an indi cator of cellular energy metabolism, fluctuates periodically in vivo; 2) th e lactate concentrations fluctuate in synchrony with insulin pulses; and 3) such coupling is more pronounced in obese, insulin-resistant individuals.