Adaptation of plasma catecholamine and corticosterone responses to short-term repeated noise stress in rats.

Plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) concentrations were determined in blood frequently sampled via a cardiac catheter from freely moving rats exposed to three successive trials of white-noise stimulation (10 min, 100 dBA) with an intertrial interval of 30 min. During the sampling period, behavioral activities of the rats were recorded. It was demonstrated that the first exposure to noise induced a specific temporal pattern of neuroendocrine changes: Plasma A and NA contents increased rapidly and peaked early after stimulus onset but their peak-latencies were different (1 and 5 min, respectively). Noise offset was followed by quick return to basal levels. The changes in plasma CS concentrations were considerably slower in onset and slower in decline. The second and third exposure to this type of stressor resulted in attenuated hormonal responses and a reduced decrement of the NA/A-ratio, concurrent with a gradually less intense behavioral reaction. This differential pattern of plasma NA, A and CS responses following repetitive exposure to identical stressors, referred to as adaptation, is discussed with regard to the biochemical changes at various levels of the neuroendocrine systems involved.