Agonistic activity of ICI 182 780 on activation of GSK 3β/AKT pathway in the rat uterus during the estrous cycle
Introduction
Antiestrogenic drugs have been developed for their ability to inhibit the physiological response of reproductive tissues to estrogen [1], [2], [3]. In the uterus, however, some antiestrogenic treatments mimic the actions of estradiol (E2) [1], [4], [5], [6]. The relative antiestrogenic and estrogenic effects depend on the antiestrogen used, the dose, the animal species and the molecular-physiological model under investigation [7], [8], [9].
ICI 182,780 (ICI) is thought to be a pure steroidal estrogen antagonist that blocks estrogen action by competing with endogenous estrogen for estrogen receptors (ER) present in the nuclei of estrogen responsive tissues [10], [11], [12], [13]. A large number of studies demonstrated that ICI antagonizes E2 induction of uterine cell proliferation and estrogen-regulated protein expression in ovariectomized (ovx) animals [14], [15], [16], [17], [18], [19], [20], [21], [22]. However, several reports indicate some estrogenic agonist effects of ICI in both in vivo and in vitro models. For example, in vitro, ICI induces 5% of E2 up regulated genes in MCF-7 cells [23], causes an increase in phosphorylation of extracellular signal-regulated kinase 1/2 (ERK 1/2) in neonatal rat primary cerebellar neurons [24], and does not block the activation of ERK1/2 induced by E2 in basal forebrain cholinergic neurons [25]. Also, in vivo, ICI increases endometrial weight and GAPDH mRNA levels in the stroma and glandular epithelium of the sheep uterus [26], induces secretion of oxytocin and prostanglandin F2 alpha in intact ewes during estrous cycle [27], potentiates the effect of E2 on plasma calcium and up regulates ERα in fish liver [28]. Taken together, these studies demonstrate that ICI display agonistic and antagonist effects on several typical estrogen responses in different tissues and models. Here, we examined whether ICI acts as an agonist or antagonist of E2 effects on uterine cell proliferation and protein kinase b/AKT pathway protein expression, in adult rat uterus during the estrous cycle.
Section snippets
Animal treatments
All procedures with animals were carried out according with the Guidelines of the Mexican Federal Law for Animal Protection and with the approval of the Laboratory Animal Care and Use Committee from Facultad de Química, UNAM. Rats were obtained from the animal center UNAM-Harlan. Adult female Wistar rats (Rattus Norvegicus) (200–250 g) were maintained under a 12:12 h light/dark cycle, lights on from 06:00 to 18:00 h, with food and water available ad libitum. Two experimental models were used: ovx
ICI 182,780 did not block BrdU DNA incorporation in cycling animals
To assess the relative efficacy of anti-estrogen ICI, the compound was first tested in ovx rats. Using BrdU incorporation after i.p. injection 2 h before death as a measure of DNA synthesis, we observed that in vehicle treated ovx rats, there was a low basal rate of DNA synthesis in both luminal and glandular epithelia (1.99 ± 0.5% and 2.21 ± 0.9% BrdU labeled cells, respectively) (Fig. 1A). As expected, E2 treatment induced a significant increase in the number of BrdU-positive luminal (20.96 ± 0.7%)
Discussion
ICI is the most complete and best characterized ER antagonist in both in vivo and in vitro models. Importantly, it has been described as a “pure” antagonist, but it is likely that this concept is not completely accurate for different functions and tissues [23], [24], [25], [26], [27], [28]. Several reports indicate some estrogenic effects of ICI in vitro and in vivo models. These results prompted us to evaluate whether ICI acts as an agonist or antagonist on uterine cell proliferation and
Acknowledgements
This work was supported by the National Council for Science and Technology (CONACyT Grant 80338), Mexico City Science and Technology Institute (ICyT D.F. 234/2010) and by PAPIIT (IN-210412) and PAIP (6190-08) from the National Autonomous University of Mexico (UNAM).
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