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Introduction
When glial cells were first described over a century ago, in the classic studies by Spanish neuroanatomists Cajal and Hortega, they were envisaged as equivalent to connective tissue, providing only support for the 'real' brain cells – the neurons. However, within the last decade it has become increasingly evident that glial cells play an active and crucial role in two fundamental areas: the development of the mammalian nervous system and the maintenance of normal brain function.
The vast majority of glial cells in the nervous system are classed as macroglia, and, based on structural characteristics, can be further subdivided into oligodendrocytes (oligodendroglia), radial glia and astrocytes (or astroglia). A much smaller group, termed microglia, develop from non-neural tissue and act as macrophages (for review see Thomas 1992). Oligodendrocytes are found in white matter and are the source of the myelin of the axon sheath; their origin and functional properties
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ABSTRACT
Receptors for angiotensin II (AII) and atrial natriuretic peptide (ANP) were characterized in a membrane fraction from resistance-type artery from human placentae. Placentae from normal pregnancies and pregnancies complicated by intrauterine growth retardation (IUGR) were studied. High- and low-affinity receptors for AII (dissociation equilibrium constant (K d) 1 ·7 and 15·7 nmol/l respectively) and ANP (K d 0·2 and 55·5 nmol/l respectively) were identified; these parameters were unchanged in IUGR, but there was a reduction in high-affinity receptor number by approximately 50% for AII and 80% for ANP in this condition. Both peptides may have a role in the regulation of fetoplacental blood flow. The alterations in IUGR are consistent with sustained activation of the fetal reninangiotensin system and suggest altered vascular responsiveness to ANP.
Journal of Endocrinology (1990) 126, 341–347
