Effects of estradiol and progesterone on the reproductive tract and on uterine sex steroid receptors in female lambs

The effects of estradiol-17 beta (E-2) and progesterone (P) on the reproductive tract and on uterine estrogen receptors and P receptors were studied in 2-mo-old female lambs (n=11). On Days 0, 1 and 2, E-2 (1 ug/kg, Group E, n=4), P (0.3 mg/kg, Group P, n=4) or corn oil (control) vehicle (Group C, n=3) were administered, and in Day 3 all lambs were slaughtered. Group E (n=12) had E-2 serum concentrations (mean +/- SEM) of 43.8 +/- 2.2 pmol/L, similar to that of the follicular phase; while P concentrations in Group P (n=12) were similar (2.8 +/- 0.18 nmol/L) to those of the luteal phase of the ewe estrous cycle. The E-2 treatment increased the reproductive tract weight, while P treatment increased only the uterine weight. Both E-2 and P receptors from upper and middle uterine zones (including the myometrium, endometrium and caruncles) were determined by binding assays with tritiated hormones, dextran-charcoal separation and inverse Scatchard analysis. Both the E-2 and P treatments decreased E-2 and P receptor concentrations in upper and middle zones, although the upper zone had higher receptor concentrations than the middle zone (P<0.01). E-2 receptor concentrations in the upper zone (mean +/- SEM, fmol/mg prot) were 1236 +/- 34, 667 +/- 80 and 444 +/- 103 for Groups C, P and E, respectively. The P receptor concentrations were 2434 +/- 135, 1273 +/- 102 and 1536 +/- 213 for the same groups. The high uterine P receptor concentrations allowed P action without prior estrogen priming of female lambs. The present results suggest that E-2 and P might down-regulate their own and each other's receptors during development. The biological responses induced by E-2 and P, as measured by the reproductive tract weight demonstrated that at an early stage of development uterine receptors are physiologically active. (C) 1997 by Elsevier Science Inc.