Pregnancy and ovarian steroid regulation of angiotensin II type 1 and type 2 receptor expression in ovine uterine artery endothelium and vascular smooth muscle

Abstract

Although pregnancy is clearly associated with refractoriness to infused angiotensin II (AII) in the uteroplacental unit, there is still dispute over the mechanism by which angiotensin type 1 and type 2 receptors (AT1R and AT2R) may mediate this response in the uterine artery. This is in large part due to incomplete knowledge of levels of AT1R and AT2R expression and function in uterine artery endothelium (UA Endo) in the nonpregnant (NP) and pregnant (P) states, combined with the disagreement on whether AII may act through release of adrenomedullary catecholamines. The authors have previously described an increase in AT1R in UA Endo but not UA vascular smooth muscle (VSM) during pregnancy as compared to the nonpregnant intact ewe. Herein they report that the pregnancy-associated increase in AT(1)R expression in UA Endo is regulated by ovarian steroids. Using a recently developed antibody to AT2R, the authors now show there is no change in AT2R in UA Endo or VSM associated with ovarian function, and although AT2R is not changed in UA Endo by pregnancy, there is a significant decrease observed in UA VSM at that time. The authors also examined changes in receptors in UA Endo and VSM in estrogen (E2beta)-primed ewes in view of the common use of this model as a control for physiologic studies. In contrast to their findings in nonprimed nonpregnant or pregnant animals, the authors observed a significant increase in both AT1R and AT2R in UA Endo in response to the supraphysiologic priming with E2beta. In order to address the possible functionality of AT1R or AT2R in UA Endo, the authors used the uterine artery endothelial cell (UAEC) model of UA endothelial cells maintained in culture to passage 4. Differences in expression of AT1R or AT2R were normalized at passage 4 in P-UAECs and NP-UAECs. Treatment with AII activated phospholipase C (PLC) in both NP- and P-UAECs but signaling through the extracellular signal-regulated kinase (ERK) pathway was dramatically enhanced in P-UAECs compared to NP-UAECs. Surprisingly, both phosphoinositol turnover and ERK2 phosphorylation responses failed to display the expected dose-responses. Inhibition of AII-stimulated ERK2 phosphorylation with antagonists DUP 753 (AT1R, 10 microM) and PD 123319 (AT2R, 10 microM) failed to selectively inhibit ERK2 phosphorylation. The authors conclude that (a) the net effect of pregnancy may be an increase in the AT1R/AT2R ratio in both UA Endo and VSM but through apparently distinct mechanisms, (b) the ovariectomized animal model is similar to the luteal state for AT1R and AT2R expression, while the E2beta-primed model does not resemble the nonpregnant or pregnant state, and (c) there is a real possibility that AII may mediate its effects either through a complex AT1R-AT2R interaction or via an as-yet unidentified non-AT1, non-AT2 receptor.