Opposite effects of short and continuous oestradiol replacement on CNS responses to hypoxic stress

Oestrogen can alter neuroendocrine responses to stress but the evidence is conflicting. We examined the effects of a short-term 17beta-oestradiol surge versus a continuous 17beta-oestradiol replacement regime on neuroendocrine cell responses to hypoxia in the ovariectomized rat. Short-term oestradiol replacement significantly increased the number of Fos-positive SON and PVN OT cells and VLM A1 and C1 cells following hypoxia. In contrast, continuous oestradiol replacement significantly decreased the number of hypoxia-induced Fos-positive mPVN, PVN OT and VLM A1 and C1 and NTS C2 cells. We propose that the effects of oestradiol replacement on stress-induced neuroendocrine responses may be dependent on whether oestrogen levels are rising rapidly or remaining constant over a relatively long period.