The Endogenous Opioids Do Not Mediate the Suckling-Induced Suppression of LH Secretion in Lactating Rats

概要

論文の詳細を見る
The effect of intravenous injection of naloxone on the suppression of LH secretion during lactation was examined in intact, ovariectomized, and ovariectomized steroid-primed lactating rats at early and late lactation. The day of parturition was designated day 0. The litter size was adjusted to 8 on day 1, and ovariectomy was performed on day 2. Progesterone alone or progesterone and estradiol in silicone capsules were implanted subcutaneously immediately after the ovariectomy. Blood samples were collected every 6 min for 3 h on day 8 and 16 in intact and ovariectomized rats and on day 16 in ovariectomized steroid-primed rats. Naloxone (total amount=1.2 mg) was injected intravenously via the sampling catheter every 6 min for 2 h after the first hour of the sampling period. Intravenous injection of naloxone had no significant effect on plasma concentrations of LH on day 8 in intact or ovariectomized lactating rats. On day 16, naloxone treatment increased the plasma level of LH in intact lactating rats but not in ovariectomized or ovariectomized steroid-primed lactating rats. The present study clearly indicates that the endogenous opioid peptides do not mediate the suppression of the LH release by suckling stimulus, since intravenous injection of naloxone did not increase the LH secretion at early lactation when the suckling stimulus is the dominant factor suppressing LH release.
日本繁殖生物学会の論文