Estrogen and progesterone receptor content in the pituitary gland and uterus of progesterone-primed and gonadotropin releasing hormone-treated anestrous ewes

The objective of this work was to investigate the effect of progesterone (P) and gonadotropin-releasing hormone (GnRH) treatment on estrogen receptor (ER) and P receptor (PR) concentrations in the pituitary gland and uterus of anestrous ewes. Ewes were either not treated (group C, n=4); were treated with 0.33 g P-controlled internal drug release (P-CIDR) for 10 days (group P, n=4), with GnRH, 6.7 ng i.v. injections every 2 h for 18 h followed by a 4 mug bolus administration of Receptal at 20 h (group GnRH, n=4), or with a combination of the P and GnRH treatment (group P + GnRH, n=3). Ewes were humanely killed either at the beginning of the experiment (group C), when the CIDR was removed (group P), or 24 h after the GnRH bolus treatment (groups GnRH and P + GnRH). Progesterone treatment increased serum P concentrations, indicating that the treatment was effective. All GnRH treated ewes had similar luteinizing hormone (LH) surges, which lasted 8 h. At slaughter, estradiol (E2) concentrations in the GnRH group were higher than in groups C, P and P + GnRH. Treatment with GnRH increased more than 10-fold the content of ER and PR in the pituitary gland without altering steroid receptor concentrations in the uterus. When GnRH was combined with P the uterine receptor contents were higher than with P treatment alone. The treatment with P decreased ER and PR content in the uterus, but had no effect on the pituitary gland. The results show that regulation by P and GnRH of ER and PR content in anestrous ewes is tissue-specific. (C) 2002 Elsevier Science Inc. All rights reserved.