Effect of gonadoreline and naloxone on induction of ovulation and plasma LH in rabbit.

Abstract

To study the effect of an opiate antagonist receptor (naloxone) on LH secretion, two groups of seven does were randomly allocated to GnRH (gonadoreline, 20 microgram/animal), and GnRH + naloxone (1.8 mg/kg b.w.) treatment, respectively and another group of eight animals was treated with naloxone alone. Blood samples were obtained immediately before treatment (0 minutes) and at 60, 120 and 180 minutes after injection. Plasma levels of LH were determined by a direct, simple and precise sandwich enzyme immunoassay (EIA), adapted for measuring plasma LH in rabbit. Luteinizing hormone reached maximum values 60 minutes after administration of GnRH or GnRH + naloxone (p < 0.05) and all the females of these 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 samples obtained at 0, 120 and 180 minutes. Results show a limited effect of this naloxone dose on the anterior pituitary of non lactating adult rabbi does in relation to induced ovulation. No synergic effect was detected when naloxone was administered in addition to gonadoreline.