Angiotensin receptors in myometrium and myometrial vessels from uteri of women during the follicular and luteal phases of the menstrual cycle and in late pregnancy

Renal Angiotensin-II Receptors Expression Changes in a Model of Preeclampsia

The blunted response to angiotensin II (Ang II) during pregnancy is lost in patients by preeclampsia. This impaired response has been attributed to a change in one or both of the Ang II receptors, type 1 (AT(1)R) and type 2 (AT(2)R). The ratio of the Ang II receptor types in the kidney has not been studied. We postulated that an imbalance exists between AT(1)R/AT(2)R receptors in the renal cortex from rats subjected to an experimental model of preeclampsia, and that this altered ratio can modify the characteristic blunted pressor response to Ang II during pregnancy. The feto-placental units of Wistar rats were made ischemic by subrenal aortic coarctation, thus creating an experimental model of preeclampsia. We measured the AT(1)R and AT(2)R protein expression and the presence of the heterodimer AT(1)R/AT(2)R in the renal cortex and evaluated the pressor response to Ang II in an isolated kidney preparation from non-pregnant, healthy pregnant, and preeclampsia model rats. Pregnancy increased AT(2)R and AT(1)R/AT(2)R heterodimer expression and decreased the pressor response to Ang II. In contrast, AT(1)R increased, while AT(2)R and AT(1)R/AT(2)R heterodimer decreased in the preeclampsia model group. Thus, Ang II hypersensitivity observed in preeclampsia might be related to an increased expression of AT(1)R over AT(2)R and to a decreased presence of the AT(1)R/AT(2)R heterodimer in renal cortex.

The regulation of uterine relaxation

The regulation of uterine relaxation is poorly understood but research in myometrial tissue and other types of smooth muscle has defined a number of receptors, ion channels and regulatory proteins that are likely to be involved. Some of these proteins are substrates for protein kinases, especially cyclic nucleotide dependent kinases. More research is necessary to identify the key molecules involved in the maintenance of uterine quiescence in pregnancy. The use of tocolytics in preterm labour remains controversial; there is a need to identify better pharmacological targets to provoke safe and selective uterine relaxation and improve neonatal outcome.

Angiotensin II-mediated calcium signals and mitogenesis in human prostate stromal cell line hPCPs

Western blots and immunocytochemistry were used to detect angiotensin 1 (AT(1)) and angiotensin 2 (AT(2)) receptors in human primary cultures of the prostate stromal compartment (hPCPs). Immunohistochemistry was performed on human prostate tissue-embedded paraffin. In addition, pharmacological tools were applied in combination with photometry experiments to characterize the physiological activity of AT(1) and AT(2) receptors in hPCPs cell culture. A proliferation assay was used to describe the mitogenic activity of angiotensin II (Ang II) on hPCPs cells. Only the AT(1) receptor was detected in Western blot analysis. Immunocytochemistry of hPCPs cells showed that the AT(1) receptor is present in both the smooth muscle type and the fibroblastic type. In the stromal compartment of human prostate tissue, immunoreaction with antibodies against the AT(1) receptor was detectable.Fura-2-loaded hPCPs cells showed an instantaneous and linear rise in free intracellular calcium ion concentration ([Ca(2+)](i)) after local perfusion with Ang II in concentrations of 10 nM. Removing of external calcium or emptying intracellular calcium stores before Ang II application diminished or abolished this [Ca(2+)](i) response. The response to Ang II was also diminished when hPCPs cells were perfused with the AT(1) receptor inhibitor losartan prior to Ang II application. No inhibition of the [Ca(2+)](i) increase was detectable after perfusion with PD 123319, a specific inhibitor of the AT(2) receptor.hPCPs cells were stimulated with Ang II in various concentrations over a period of 2 days. The subsequently performed proliferation assay revealed a mitogenic effect of Ang II on hPCPs in concentrations starting at 10 nM. This effect could be inhibited by losartan.

Angiotensin II regulation of ovine fetoplacental artery endothelial functions: interactions with nitric oxide

During normal pregnancy, elevated angiotensin II (Ang II) concentrations in the maternal and fetal circulations are associated with dramatic increases in placental angiogenesis and blood flow. Much is known about a local renin-angiotensin system within the uteroplacental vasculature. However, the roles of Ang II in regulating fetoplacental vascular functions are less well defined. In the fetal placenta, the overall in vivo vasoconstrictor responses of the blood vessels to Ang II infusion is thought to be less than that in its maternal counterpart, even though infused Ang II induces vasoconstriction. Recent data from our laboratories suggest that Ang II stimulates cell proliferation and increases endothelial nitric oxide synthase (eNOS) and production of nitric oxide (NO) in ovine fetoplacental artery endothelial cells. These data imply that elevations of the known vasoconstrictor Ang II in the fetal circulation may indeed play a role in the marked increases in fetoplacental angiogenesis and that Ang II-elevated endothelial NO production may partly attenuate Ang II-induced vasoconstriction on vascular smooth muscle. Together with both of these processes, the high levels of Ang II in the fetal circulation may serve to modulate overall fetoplacental vascular resistance. In this article, we review currently available data on the expression of Ang II receptors in the ovine fetal placenta with particular emphasis on the effects of Ang II on ovine fetoplacental endothelium. The potential cellular mechanisms underlying the regulation of Ang II on endothelial growth and vasodilator production are discussed.

Current topic: the uteroplacental renin-angiotensin system

The components of the renin-angiotensin system (RAS) are expressed in the uteroplacental unit. The expression varies between species, probably due to the marked species differences in placental architecture. The conditions for angiotensin (Ang) II formation exist and Ang II receptors are present throughout the human uteroplacental unit, indicating the presence of a functional local RAS. The uteroplacental RAS interacts with other regulatory systems and in this way modulates various aspects of tissue function. It is suggested that the uteroplacental RAS is important for the regeneration of the endometrium after shedding, and for decidualization, implantation and placentation. The RAS participates in the regulation of the uteroplacental blood flow, prostaglandin synthesis and oestradiol secretion. Disturbances of the uteroplacental RAS may lead to dysfunctional bleeding and to reduced uteroplacental blood flow in pregnancies complicated by pre-eclampsia and intrauterine growth retardation.

Specific pregnancy-induced angiotensin II type-1 receptor expression in ovine uterine artery does not involve formation of alternate splice variants or alternate promoter usage

Recently we reported that pregnancy is associated with a dramatic increase in angiotensin II type-1 receptor (AT1-R; both protein and mRNA) in ovine uterine artery endothelial cells (UAEC), which far exceeds that seen in omental (systemic) arteries. Recent reports also suggest that alternate splicing of AT1-R mRNA may play a role in regulation of AT1-R expression in humans. Herein, we have investigated the possibility of alternate transcript splicing/promoter usage in UAEC from pregnant ewes by 5'-RACE (rapid amplification of cDNA 5'-ends). To provide our control "reference" sequences, we first performed 5'-RACE analysis of AT1-R mRNA transcripts in liver, kidney, and adrenal cortex. Analysis of 17 resultant clones showed exceptional homology, indicating that a single identically spliced mRNA product is observed in all three ovine tissues. Homology of the 5'-untranslated region to that of the human was low (34.2%), but four in-context start/stop codons and the beginning of human exons 1 and 5 were highly conserved. Subsequently we isolated 30 individual clones using UAEC RNA from three pregnant ewes and found no evidence of any sequence formed through unique splicing or promoter usage. We conclude that the pregnancy-induced increase in AT1-R expression unique to UAEC during pregnancy is not mediated by splicing of a unique transcript or unique promoter usage.