The Central Effect of β ‐Endorphin and Naloxone on The Biosynthesis of Gn RH and Gn RH Receptor (Gn RHR ) in The Hypothalamic‐Pituitary Unit of Follicular‐Phase Ewes

The effects of prolonged, intermittent infusion of β ‐endorphin or naloxone into the third cerebral ventricle of follicular‐phase ewes on the expression of genes encoding Gn RH and Gn RHR in the hypothalamus and Gn RHR in the anterior pituitary gland (AP) were examined by an enzyme‐linked immunoabsorbent assay. Activation or blockade of μ ‐opioid receptors significantly decreased or increased the Gn RH concentration and Gn RHR abundance in the hypothalamus, respectively, and affected in the same way Gn RHR quantity in the AP gland. The changes in the levels of Gn RH and Gn RHR after treatment with β ‐endorphin as well as following action of naloxone were reflected in fluctuations of plasma LH concentrations. On the basis of these results, it is suggested that β ‐endorphinergic system in the hypothalamus of follicular‐phase ewes affects directly or via β ‐endorphin‐sensitive interneurons Gn RH and Gn RHR biosynthesis leading to suppression in secretory activity of the hypothalamic‐pituitary axis.