Bibian van der Voorn

183 GENDER-SPECIFIC HPA AXIS REACTIVITY IN CHILDHOOD different levels along the HPA axis: standard ACTH tests stimulate the adrenals directly, while psychological tests are indirect stimuli of the adrenal cortex through activation of the limbic system. Moreover, the diurnal rhythm and CAR are largely controlled by the suprachiasmatic nucleus, which influences CRH release from the paraventricular nucleus. 108 Additionally, males seem to have a “fight or flight” reaction, with a stronger response when confronted with an achievement challenge (in which you can succeed or fail at a task), while women show a “tend or befriend” response, and therefore seem to be more sensitive to stress tests that incorporate social rejection or peer pressure. 82,109,110 This might be due to the previously mentioned HPA/HPG axes interactions, as well as possible sexually dimorphic site-specific GR and MR expression patterns in the brain. 2,81 Consequently, when designing a study, it is important to realize what type of stress and which level of the HPA axis is aimed to be tested. Subsequently, the effect of gender on that specific type of stressor should be taken into account. We recommend using standardized protocols, since gender- specific effects on HPA axis reactivity have been best described with regard to standardized stress protocols. Additionally, comparing the results of the studies included in our systematic review was hampered by the fact that data were collected and presented in numerous ways. For the same reason, it was impossible to perform a meta-analysis. Moreover, only limited information was often provided, and it is therefore possible that (subtle) sex differences were not found. This was the case for all categories of HPA axis reactivity discussed in this review. In order to draw more precise conclusions concerning gender differences in HPA axis reactivity in childhood, we wish to argue using standardized protocols, as well as a standardized presentation of results for future studies on HPA axis reactivity. Seeman and Robbins (1994) 111 have defined stress resiliency as “the overall pattern of HPA response to challenge”, which includes the rate of initial response, the magnitude of the response and the rate of recovery of the HPA axis. In order to be able to draw conclusions on all of these aspects, and to enable unbiased, quantitative comparisons, reporting data on HPA axis reactivity should take all of these aspects into account. This can be done by both reporting absolute cortisol values (e.g., minimum and maximum cortisol levels) as well as derived variables (e.g., time to peak/recover, delta cortisol, ascending/descending slopes and areas under the curve), preferably analyzing sex differences for all these parameters. This will allow a full appreciation and overview of the course followed by cortisol pre- and post-stressor.