ACTH:CORT ratio. Because Pb exposure was associated with increased ACTH and lower CORT at baseline, we repeated the regression analyses using the ACTH:CORT ratio as the outcome measure (Table 4). BPb was posi tively associated with the ratio at all time points, although the association was not significant at 75 min. In addition, TPb was a significant predictor of the ratio at 5, 10, and 15 min posts tressor (Table 4). The ACTH:CORT ratio was 14–23% greater in association with an IQR increase in log-BPb and 15–19% greater with an IQR increase in log-TPb. Figure 2 displays the average ACTH:CORT ratios over the experimental time course for the low and high BPb groups (median split). Regression analyses with the median split led to similar results (data not shown). This is indicative of a diminished adrenal responsiveness to endogenous ACTH (Nater et al. 2010).
Sensitivity analyses. We defined “nonresponders” as individuals who failed to produce any increase above their own baseline for both ACTH and CORT responses to the TSST (i.e, values at 5 min and thereafter were equal or lower than baseline at minute 0; n = 5). When nonr eponders were excluded, results for ACTH and CORT were similar to those reported for the entire sample (data