Effect of naloxone on the development of the positive feed-back action of oestrogen-progesterone on LH secretion in rats.

The purpose of this study was to examine the role of opiate peptides in the development of the positive feedback effect of ovarian hormones (Oe-P) on the LH secretion that matures in female rats at about the age of 20-22 days. Oe-P administration at the age of 14 days induced a significant decrease of LH levels. A single injection of naloxone (5 mg/kg) induced a significant release of LH. This release was completely blocked by Oe-P administration. At the age of 20 days, Oe-P did not induce any significant change of LH levels, whereas naloxone increased the serum LH concentration. On the other hand, injection of Oe-P into naloxone-treated rats induced a significant rise in LH that was significantly higher than that observed with naloxone alone (P less than 0.025). Oe-P administration induced a positive feedback effect on LH at the age of 25 days. At this age, naloxone also increased LH levels and a significant potentiation of the LH release in response to Oe-P was observed in a group treated with naloxone. These results indicate that naloxone advances the development of the positive feedback mechanism of ovarian hormones on LH secretion and potentiates this mechanism after its maturation. On this basis it is proposed that the probable inhibitory effect of opiates on the onset of the positive feedback mechanism is related to the well-known participation of the opiate system in the onset of puberty.(ABSTRACT TRUNCATED AT 250 WORDS)