Rapid fluctuations in plasma catecholamines in monkeys under undisturbed conditions

We have demonstrated in monkeys and in man sustained synchronous oscillations in plasma levels of insulin, C-peptide, glucagon, and glucose that have periods ranging from 8 to 11 min. To identify the mechanisms of these oscillations, we studied plasma levels of catecholamines in search for periodic fluctuations. Blood was obtained at 2-min intervals from fasting, undisturbed, chair-adapted male rhesus monkeys via chronically implanted central venous catheters. Plasma levels of epinephrine, norepinephrine, and dopamine were measured by a radioenzymatic assay. Large fluctuations in plasma epinephrine were observed with an average peak-to-trough amplitude of 34 pg/ml at a mean level of 122 pg/ml. Similar fluctuations in norepinephrine and dopamine occurred and were correlated to those of epinephrine: r = 0.51 and 0.35, respectively. The most common periodicity in all three catecholamines was 6-13 min/cycle as determined by spectral analyses. Cross-correlation analyses indicated that fluctuations in the catecholamines were significantly negatively correlated with oscillations in insulin and were unrelated to fluctuations in glucagon. These fluctuations in plasma catecholamines may be related to mechanisms controlling the periodicity observed in plasma insulin and glucose.