Levels of Dopamine β Hydroxylase Immunoreactivity in the Preoptic Hypothalamus of the Ovariectomised Ewe Following Injection of Oestrogen: Evidence For Increased Noradrenaline Release Around the Time of the Oestrogen‐Induced Surge in Luteinizing Hormone

We have measured dopamine beta hydroxylase (DBH) immunoreactivity in the preoptic hypothalamus as an index of release of noradrenaline in the ovariectomised (OVX) ewe at the time of an oestrogen-induced surge in luteinizing hormone (LH) release. OVX ewes (n=5) were given an injection of 50 microg oestradiol benzoate (or oil), which causes a surge in the secretion of LH. Blood samples were taken and sheep were killed 16 h later. Other groups (n=3) were given oil or oestrogen and killed 6 h later. Brains were collected for immunohistochemistry and image analysis. The number of DBH-stained cells and the integrated optical density of the cells was measured throughout the A1 field of the brainstem. The DBH staining was measured in the terminal beds of the hypothalamus. There was no difference between the controls and the EB-treated OVX ewes in the number of DBH positive cells or the optical density of DBH-staining cells in the A1 field. Within the preoptic area, there was reduced (P<0.02) DBH staining in the 16 h EB-treated ewes. There was no change in the DBH staining in the paraventricular nucleus or the arcuate nucleus of the hypothalamus. These data suggest that there is release of noradrenaline in the preoptic area at the time of the E-induced GnRH/LH surge in the OVX ewe.