Pituitary uptake of 125I-D-Leu6, Des-Gly N2(10) LH-RH-ethylamide in ovariectomized rats pretreated with oestradiol-17 beta.

The objective of this study was to determine if pretreatment of ovariectomized rats with oestradiol-17 beta affects the anterior pituitary uptake of 125I-D-Leu6, Des-Gly NH2(10)-LH-RH-ethylamide (125I-D-Leu6-LH-RH). Oestradiol-17 beta (0.5 microgram/0.5 ml oil) or oil was administered to ovariectomized rats at 2, 4, 8, 12, 16, 20 or 24 h before death, and at 30 min before death, 5 ng 125I-D-Leu6-LH-RH were injected intravenously. The serum LH response to analogue administration in oil-treated rats did not change over time, but that in oestradiol-treated rats was depressed for 4 h and restored 8-24 h after oestradiol treatment, with the greatest response being at 16 h. However, the pituitary (adrenal, CNS cortex and thyroid) uptake of 125I-D-Leu6-LH-RH in oestradiol-treated and control rats did not change over the 24-h time period. These data suggest that oestradiol-17 beta does not affect pituitary responsiveness to 125I-D-Leu6-LH-RH by inhibiting or facilitating the uptake of this analogue by the anterior pituitary.