The plasma levels of ACTH following exposure to stress or nicotine.

Plasma ACTH and corticosterone profiles were measured following the intraperitoneal injection of nicotine or ACTH, or following exposure of rats to unpredictable stress. The elevation in plasma corticosterone was biphasic in nature in all cases, whereas plasma ACTH levels demonstrated only a single peak which rapidly declined to a sustained plateau level. The evidence supports the hypothesis that the adrenal cortex may exert a differential response to a single plasma peak in ACTH. The level of ACTH during its plateau phase may effect the duration rather than the magnitude of the corticosterone elevation. The differences between the ACTH and corticosterone profiles, resulting from the three different stimuli, are discussed.