Abstract
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.
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