Control of the fetoplacental circulation

Abstract

This year marks the 250th anniversary of the discovery by William Hunter of the existence of two distinct circulations within the human placenta. Until relatively recently the placenta has been viewed with “respect” – a passive structure which occasionally elicited fear and anxiety if implanted either too low or too deep. More recently our understanding of perinatal physiology, blood flow regulation and epidemiological data linking prenatal events with adult disease has created renewed interest in the placenta. This review will focus on the regulation of fetal blood flow in the placenta, the possible mechanisms whereby it may be deranged and why this might be relevant to adult disease.

Electron-microscopic immunolabelling of vasoactive substances in human umbilical endothelial cells and their actions in early and late pregnancy

“…Nitric oxide synthase (NOS) has been localised in these endothelial cells, although most known endothelial-dependent vasodilators have no effect on these vessels (Sexton et al 1995). Attenuation or loss of the response to the endothelial vasodilator may be significant in certain pathological conditions, where loss, or damage of the endothelial cells affects their ability to produce and release the vasodilator signal, such as in pre-eclampsia or intrauterine growth retardation, where increased vascular resistance is observed (Macara et al 1993).…”

Adrenomedullin, a New Vasoactive Peptide, Is Increased in Preeclampsia

“…Because placenta lacks autonomic innervation, uteroplacental perfusion is regulated mainly by systemic blood pressure changes through the action of both circulating and locally released vasoactive agents. 3 The role of endothelial cells in the modulation of vascular tone has been extensively demonstrated, and abnormal endothelial function in preeclampsia could contribute to an increase in peripheral resistance. 4 Adrenomedullin is a novel hypotensive peptide first isolated from human pheochromocytoma eliciting a long-lasting vasorelaxant action.…”

Adrenomedullin in mammalian embryogenesis

“…In fact, the above-mentioned expression of AM in the villous mesenchyma together with the AM reported angiogenic properties (Nikitenko et al, 2000;Zhao et al, 1998), are suggestive of a possible role of this peptide in placental vasculogenesis at the early postimplantation stages. Because the placenta lacks autonomic innervation, the maintenance of an adequate uteroplacental perfusion is regulated mainly by systemic blood pressure changes through the action of both circulating and locally released vasoactive agents (Jaffe, 1998;Macara et al, 1993), keeping the placental vasculature in a state of near-maximal dilatation. It is noteworthy that the content of immunoreactive AM in placentas (117.7 Ϯ 7.8 pg/mg wet tissue) and fetal Fig.…”

“…Peripheral resistance, mean arterial pressure, and sensitivity to vasopressor agents are reduced, whereas cardiac output, heart rate, and blood volume are increased (Carbillon et al, 2000;Macara et al, 1993). AM has been characterized as a key player in the modulation of blood pressure and vascular homeostasis in adult life through its well-documented vaxorelaxant effects (Kitamura and Eto, 1997;Letizia et al, 1999;Nuki et al, 1993).…”