Low-frequency ultradian insulin rhythms are coupled to cardiovascular, autonomic, and neuroendocrine rhythms

Plasma insulin levels were assayed to compare with earlier reported rhythms of the cardiovascular, autonomic, and neuroendocrine systems in 10 resting normal adults over 5-6 h. Our earlier report included time-series analysis for impedance cardiography measures of stroke volume, heart rate, cardiac output, thoracic fluid index, ejection velocity index, and ventricular ejection time; automated cuff measures of systolic, diastolic, and mean arterial pressures; the nasal cycle as a marker of lateralized autonomic tone; and indwelling venous catheters for sampling blood every 7.5 min to assay for adrenocorticotropic hormone, luteinizing hormone, epinephrine, and norepinephrine. Insulin was later assayed from the same plasma samples. Time-series analysis using the fast orthogonal search method of Korenberg detected insulin periodicities at ranges of 220-340, 115-145, 70-100, and 40-65, with significance across subjects at ranges of 115-145, 70-100, and 40-65 min. Significant periods for the other parameters were reported earlier at 220-340, 170-215, 115-145, 70-100, and 40-65 min, with periods at 115-145, 70-100, and 40-65 min dominating across parameters. These results suggest that insulin secretion has a common pacemaker (the hypothalamus) or a mutually entrained pacemaker with the autonomic, cardiovascular, and neuroendocrine systems.