Chapter 8 Growth Control in the retinal microvasculature

The pericyte: cellular regulator of microvascular blood flow

The vascular system - through its development, response to injury, and remodeling during disease - constitutes one of the key organ systems sustaining normal human physiology; conversely, its dysregulation also underlies multiple pathophysiologic processes. Regulation of vascular endothelial cell function requires the integration of complex signals via multiple cell types, including arterial smooth muscle, capillary and post-capillary pericytes, and other perivascular cells such as glial and immune cells. Here, we focus on the pericyte and its roles in microvascular remodeling, reviewing current concepts in microvascular pathophysiology and offering new insights into the specific roles that pericyte-dependent signaling pathways may play in modulating endothelial growth and microvascular tone during pathologic angiogenesis and essential hypertension.

Does dark adaptation exacerbate diabetic retinopathy? Evidence and a linking hypothesis

The paper reviews evidence that before any change in diabetics' fundi, changes occur to blood flow, ERG and visual functions. In the case of colour vision and contrast sensitivity, the changes are partially reversed by breathing oxygen, and therefore are the result of retinal hypoxia. There are also other evidences that hypoxia is a major factor in the development of diabetic retinopathy (DR). Therefore in diabetics with early retinopathy, but normal photopic vision, functional disturbance might appear in dark adaptation, since in such circumstances, (as shown by Linsenmeier and his colleagues) the already low retinal PO2 markedly decreases. This hypothesis has been tested and results consistent with the hypothesis (and with a number of older reports) have been obtained. The significance of this finding to early DR is discussed, and a mechanism suggested whereby prolonged periods of hypoxia during dark adaptation could generate changes in retinal capillaries. Such periods occur each night, and their elimination in diabetics could be therapeutic.

Growth factors in retinal diseases: proliferative vitreoretinopathy, proliferative diabetic retinopathy, and retinal degeneration

The goal of this review is to present the current knowledge on specific growth factor involvement in posterior segment eye disease. Growth factors can be defined as multifunctional signals which modify cell growth or proliferation, alone or in concert, by binding to specific cell surface receptors. Their biological effects on cells include cell adhesion, migration, survival, differentiation, extracellular matrix secretion, protease and protease inhibitor release, production of other growth activities, and angiogenesis. Growth factors couple the cell to the microenvironment. As some growth factors are soluble mediators of wound repair and angiogenesis, it seems possible that proliferative vitreoretinopathy and proliferative diabetic retinopathy are caused or aggravated by these factors. Other factors act as survival factors and can possibly prevent retinal degeneration. The multifunctional nature of growth factors makes it probable that practical uses will be found for these agents in the future.