Figure 1.

Examples of plasma corticosterone levels sampled every 10 min for 24 h in adult rats that had been neonatally injected with either sterile saline (Upper) or endotoxin (Lower). The diurnal pattern of steroid secretion is observable, with peak levels during the dark phase of the light cycle (1900–0500) and a nadir early in the light phase. Dotted lines indicate the mean corticosterone levels over 24 h, and it was observed that on average ENDO animals exhibited greater overall levels of corticosterone. Analysis of the ultradian secretion patterns revealed that ENDO animals exhibited more pulses of corticosterone secretion and greater pulse amplitudes compared with SALINE animals (see Table 1).