An investigation of hypothalamic-pituitary-adrenal axis hyperactivity in anorexia nervosa: the role of CRH and AVP.

We hypothesised that hypothalamic-pituitary-adrenal (HPA) axis hyperactivity in anorexia nervosa (AN) is associated with (a) elevated arginine vasopressin (AVP) activity and (b) enhanced pituitary sensitivity to AVP, as it is in depressive illness. 16 Healthy women and 18 women with active AN participated in a combined dexamethasone (DXM)/corticotrophin releasing hormone (CRH) challenge test and an AVP challenge test. This combination of tests is designed to assess the functional contribution of AVP to HPA axis activity. 10 of the active AN group repeated participation after weight gain. The cortisol response to AVP was reduced by 138% in the active AN group, suggesting an impairment of pituitary sensitivity to AVP, which began to normalise with weight gain. The cortisol and adreno-corticotrophin (ACTH) responses to the DXM/CRH test were not significantly enhanced in the active AN group, suggesting that there was no elevated endogenous AVP activity augmenting the response to CRH in AN. Weight gain was associated with blunting of the endocrine response to the DXM/CRH test, which may have been related to rising oestrogen levels. Thus, contrary to the hypotheses, we did not find (a) evidence of upregulated AVP activity or (b) enhanced pituitary sensitivity to AVP in AN. These findings suggest that the mechanism of HPA axis hyperactivity differs in depression and AN, with greater involvement of AVP in depressive disorder and perhaps more reliance on CRH to drive the axis in AN. The powerful anorexigenic effect of CRH could contribute to the severity of weight loss associated with AN.