The effects of morphine sulphate on hypothalamic glutamate levels and serum LH hormone concentration in male rats

Morphine exerts inhibitory effects on GnRH/ LH hormones secretion via the effects on the activity of different intra hypothalamic interneurons. In the present study, the effects of morphine sulphate were investigated on LH secretion via monoamine glutamate in male rats. Twenty adult male Wistar rats weighing 200- 250g in two group (n=10 in each group) received saline or one microgram morphine via third cerebral ventricle. Then each group divided in two groups. Blood samples were collected before injections and at 30 or 60 min after saline or morphine injections. Hypothalamic samples were dissected 30 or 60 minutes after injections. Serum LH hormone concentration was measured by the radioimmunoassay method and hypothalamic glutamate levels was measured by high performance liquid chromatography (HPLC). Morphine decreased mean serum LH concentration at 30 or 60 min after injections compared to before injections of morphine however this decrease was statistically significant only at 60min group. Also, morphine significantly decreased mean hypothalamic glutamate levels at 30 min after injections compared to 30 min after injections of saline group. Decrease of hypothalamic glutamate neurons activity may be involved in the morphine neural pathways controlling the inhibitory effects of morphine on LH secretion