The technology required to produce the ERKO condition is not currently available for large domestic ungulates. However, when compared to findings for vehicle-treated controls, administration of the antiestrogen ICI 182,780 to neonatal pigs from birth reduced both endometrial thickness and uterine gland penetration depth on PND 7 and PND 14. These antiuterotropic effects of ICI 182,780, considered in light of data presented here, can be interpreted to suggest that normal postnatal maturation of the uterine wall requires both development and activation of an endometrial ER system in the pig. buy asthma inhaler
The apparent requirement for development and activation of an endometrial ER system as part of the normal postnatal uterine organizational program in the pig need not be interpreted to indicate that critical uterine organizational events are estrogen dependent. Indeed, as discussed above, many if not all of the morphogenetic and cytodifferentiative events characteristic of endometrial development between birth and PND 60 in the pig may occur independently of any requirement for steroid support. Further, it is not likely that the porcine uterus is normally exposed to consistently elevated levels of endogenous ovarian estrogen during the early neonatal period. Therefore, while critical experiments remain to be conducted, the possibility exists that porcine endometrial development in the early postnatal period is estrogen independent, but ER dependent. Support for this concept comes from recent studies indicating that ER can be activated in the absence of estrogen through cross talk between membrane receptor-mediated signal transduction systems, used classically by peptide growth factors, cytokines and neurotransmitters, and the nuclear ER signal transduction complex.