EFFECT OF GONADORELINE AND NALOXONE ON INDUCTION OF OVULATION AND PLASMA-LH IN RABBIT

To study the effect of an opiate antagonist receptor (naloxone) on LH secretion, two groups of seven does were randomly allocated to GnRH (g onadoreline, 20 mu g/animal), and GnRH + naloxone (1.8 mg/kg b.w.) tre atment, respectively and another group of eight animals was treated wi th naloxone alone. Blood samples were obtained immediately before trea tment (0 minutes) and at 60, 120 and 180 minutes after injection. Plas ma levels of LH were determined by a direct, simple and precise sandwi ch enzyme immunoassay (EIA), adapted for measuring plasma LH in rabbit . Luteinizing hormone reached maximum values 60 minutes after administ ration of GnRH or GnRH + naloxone (p < 0.05) and all the females of th ese groups ovulated. Only 25% of naloxone treated rabbit does ovulated and these animals presented a high LH plasma level at 60 minutes post -treatment (p < 0.05). In non ovulated animals no variations in plasma LH concentrations were observed at 60 minutes, in relation to blood s amples obtained at 0, 120 and 180 minutes. Results show a limited effe ct of this naloxone dose on the anterior pituitary of non lactating ad ult rabbit does in relation to induced ovulation. No synergic effect w as detected when naloxone was administered in addition to gonadoreline .