Fatty messenger molecules

Failure to synthesise sufficient surfactant or the synthesis of abnormal surfactant, so that surface tension cannot be lowered, may play a role in several conditions respiratory distress syndrome of the newborn sudden infant death ( cot death ) and adult respiratory distress syndrome. The enzymes involved in the synthesis of surfactant only appear during the third trimester of pregnancy, so that surfactant is not produced in premature babies and they have difficulty breathing. 

The metabolic disturbances in these conditions are as expected from a shortage of oxygen dependence of tissues on glycogen conversion to lactate (which results in lactic acido- 

Artificial surfactant, which contains dipalmitoylphosphati-dyl choline and some palmitic acid to provide for spreadability, is now commercially available for instillation into the lung. Adminishation of steroids to the mother prior to birth of the premature infant is also carried out. 

Myelin is the material that surrounds some neurons and their axons but it is not a single compound. It is a 

Ceramide is now included in some skin creams which are claimed to be beneficial to the skin, preventing drying and reducing the effects of ageing. Linoleoyl-ceramide is present in the skin where it restricts water permeability, preventing excessive water loss from the skin. 

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Fatty messenger molecules include diacylglycerol, ceramide, platelet activating factor, the eicosanoids and resolvins. A summary of the reactions that produce some of these messengers is given in Appendix 11.7. 

Figure 7.10 Hormones that regulate the activity of the hormone-sensitive lipase in adipose tissue. Each hormone binds to a receptor on the outside of the plasma membrane and changes the activity of the lipase within the adipocyte, via a messenger molecule (Chapter 12). A hormone - independent lipase is also present with provides a low rate of release of fatty acid when the former is inactive.

Detailed analysis of phospholipids, as well as neutral lipids and nonesterified fatty acids, has become progressively more important as these molecules have come to represent intercellular messenger molecules that are involved in a number of disease states. The analysis of lipid patterns of blood and lipoproteins may therefore constitute a useful diagnostic tool. As noted in the previous edition, suitable methods for phospholipid analysis are often time consuming and tedious, since most of them include several separation and derivatization steps. 

Fatty acids are components of a rich variety of complex lipid molecules that play critical structural roles in membranes. Some of these lipids are also the precursors of compounds with hormone or second-messenger activities. In this chapter we focused on the metabolism of these compounds with some mention of their functions. The following points are the highlights of our discussion. 

Thus far we have been concerned with the metabolism of fatty acids in relationship to the storage and release of energy. In chapter 19, Biosynthesis of Membrane Lipids, we focus on the metabolism of lipids that serve other roles. Many types of lipids are essential membrane components. A number of lipids also function as metabolic signals in response to hormonal signals. These lipid molecules are known as second messengers. 

Roles Fatty acids have four major biological roles 1. They are components of membranes (glycerophospholipids and sphingo- lipids) 2. Several proteins are covalently modified by fatty acids 3. They act as energy stores (triacylglycerols) and fuel molecules 4. Fatty acid derivatives serve as hormones and intracellular second messengers. 

Fatty acids are physiologically important as (1) components of phospholipids and glycolipids, (2) hydrophilic modifiers of proteins, (3) fuel molecules, and (4) hormones and intracellular messengers. They are stored in adipose tissue as triacylglycerols (neutral fat). 

Arachidonate, an essential precursor of prostaglandins and other signal molecules, is derived from linoleate. This 20 4 polyunsaturated fatty acid is the precursor of several classes of signal molecules— prostaglandins, prostacyclins, thromboxanes, and leukotrienes— that act as messengers and local hormones because of their transience. They are called eicosanoids because they contain 20 carbon atoms. Aspirin (acetylsalicylate), an anti-inflammatory and antithrombotic drug, irreversibly blocks the synthesis of these eicosanoids. 

As expected, earlier studies focused on mechanisms that involve eicosanoid metabolites. More recently, however, the effects of fatty acids on gene expression have been investigated and this focus of interest has led to studies at the molecular level (Tables 8, 9). Previous studies have shown that fatty acids, whether released from membrane phospholipids by cellular phospholipases or made available to the cell from the diet or other aspects of the extracellular environment, are important cell signaling molecules. They can act as second messengers or substitute for the classic second messengers of the inositide phospholipid and cyclic AMP signal transduction pathways. They can also act as modulator molecules mediating responses of the cell to... 

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