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Letters to the Editor |
Baker Medical Research Institute, Prahran, 8008 Victoria, Australia
The question of habituation or facilitation of hormonal responses to stress with repeated testing is a complex one (1, 2). It is true that with psychological stress glucocorticoid responses have been shown to decrease when subjects are exposed to the same stressor repeatedly in close proximity. This is the case for the studies quoted by Kirschbaum et al. (3) and Deinzer et al. (4), in which exposure to stress occurred either daily or several times a day. In our study (5), by contrast, the two tests were administered 8 weeks apart and in the placebo-treated subjects. There was no evidence of a decrement in the responses of any of the variables measured between the 2 days, suggesting that in this group neither an habituation nor a facilitation effect occurred. The subjects treated with estradiol, however, showed significant reductions in glucocorticoid, catecholamine, and blood pressure responses. Elimination of confounding effects, such as habituation, to stress is one of the strengths of the placebo-controlled design.
It is well documented that baseline values for glucocorticoid and catecholamine levels vary considerably between individuals, as do responses to stress (6, 7, 8). However, baseline levels are relatively stable for individual subjects (6, 9), a fact that is consistent with the finding that a substantial part of the variance is genetic in origin (10, 11). Accordingly, it remains possible to make comparisons between treatment groups if the statistical analysis is carried out within rather between subjects, as we have done. Once again, the fact that significant differences were obtained in the women treated with estradiol but none in the placebo group provides strong evidence in support of our conclusions.
In our study, we did not attempt to correlate subjective responses and personality traits with hormonal responses. This would be of undoubted interest, although the recent work of Schommer et al. (12) suggests that the two sets of variables may be independent.
References
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