Allopregnanolone and dehydroepiandrosterone response to corticotropin-releasing factor in patients suffering from Alzheimer's disease and vascular dementia

Abstract

Objective: Neurosteroids have been suggested to be involved in the regulation of cognitive performances. A major neurosteroid gamma-aminobutyric acid (GABA) agonist is allopregnanolone: the main source of circulating allopregnanolone is the adrenal cortex. Studies indicated that a disturbance of the central regulation of the hypothalamic-pituitary-adrenocortical axis occurs in both senile (Alzheimer's disease: AD) and vascular dementia (VD).

Design: The aim of the present study was to evaluate the levels of circulating allopregnanolone, dehydroepiandrosterone (DHEA) and cortisol and their response to corticotropin-releasing factor (CRF) test in AD and VD.

Methods: Three groups of 12 subjects were included in the study: AD, VD and age-matched control subjects. CRF test was performed in all subjects and allopregnanolone, DHEA and cortisol levels were measured every 15min for 2h.

Results: Mean +/- s.e.m. allopregnanolone and DHEA basal levels were significantly lower in AD and VD than in controls, while cortisol levels were significantly higher than in controls (P<0.01). Allopregnanolone and DHEA levels increase in response to CRF test in all subjects but the area under curve (AUC) in patients was significantly lower than in controls (P<0.01). Cortisol secretion appeared to be very sensitive in response to CRF stimulation: in fact, cortisol response to CRF test in AD and VD subjects was higher (both as AUC and as % max increase) than in controls (P<0.01).

Conclusions: The present study firstly showed that allopregnanolone levels are reduced both in AD and in VD and that dementia has a preserved stimulated response of allopregnanolone to CRF. Overall, however, the total response of allopregnanolone to CRF remains reduced in respect to controls. Further studies are necessary for a better understanding of the role of neurosteroids in the regulation of cognitive function.