Effects of estradiol and progesterone on the reproductive tract and on uterine sex steroid receptors in female lambs
1997
The effects of estradiol-17 beta (E2) 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, E2 (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 E2 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 E2 treatment increased the reproductive tract weight, while P treatment increased only the uterine weight. Both E2 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 E2 and P treatments decreased E2 and P receptor concentrations in upper and middle zones, although the upper zone had higher receptor concentrations than the middle zone (P<0.01). E2 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 E2 and P might down-regulate their own and each other's receptors during development. The biological responses induced by E2 and P, as measured by the reproductive tract weight, demonstrated that at an early stage of development uterine receptors are physiologically active.
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