Investigation of the Uptake, Metabolism and Delivery of Polyunsaturated Fatty Acids in the Developing Avian Embryo

Denis, Raphael (1998) Investigation of the Uptake, Metabolism and Delivery of Polyunsaturated Fatty Acids in the Developing Avian Embryo. MSc(R) thesis, University of Glasgow.

Abstract

The avian embryo exhibits a range of unique features which favour its suitability as a model for investigating polyunsaturated fatty acid (PUFA) metabolism and transport. Recent evidence has shown that metabolic remodelling of yolk fatty acid moieties occur in the yolk complex, especially the transfer of docosahexaenoic acid (DHA) from phospholipid (PL) fraction in the yolk to triacylglycerol (TG) fraction in the blood. Moreover a preferential disappearance of yolk DHA associated with the phospholipid fraction specifically phosphatidylethanolamine, had been described at around day 12. A phospholipase A2 was found to be involved in this process coincident with an increase of DHA within the free fatty acid fraction in the yolk. Fatty acid metabolism in the yolk sac membrane during embryonic development has been studied. The activities of key regulatory enzymes of acyl glycerolipid synthesis and oxidation were measured; carnitine palmitoyltransferase I, monoacylglycerol acyltransferase, glycerolphosphate acyltransferase and diacylglycerol acyltransferase. Maximal CPT I activity was found at day 12 and significantly declined to day 18. The MGAT activity remained constant throughout development suggesting that this pathway of glycerolipid biosynthesis may provide a mechanism to selectively retain essential PUFAs during a period of intense fatty acid oxidation. The measured activity of microsomal GPAT was noticeably lower compared to MGAT, with peak activity at day 12. The presence of DGAT activity completes the TG synthetic pathway which is released into the embryonic blood as part of very low density lipoproteins (VLDL). Characterisation and analysis of lipoprotein lipid in the blood at day 14 and day 22 extended the knowledge regarding the delivery system of DHA in the avian embryo. The VLDL TG was hydrolysed by lipoprotein lipase with the accompanying uptake of fatty acids into the adipose tissue. Hydrolysis of TG containing DHA by LPL appeared to be less active towards other TG species resulting in an enrichment of DHA in the TG of resulting lipoproteins which would be cleared by the liver. The results suggest that the yolk sac membrane has an important role in the regulation of DHA delivery to the developing embryo. Moreover the supply of DHA to the neural tissues in the developing embryo appears to be coordinated by both the adipose tissue and liver.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Additional Information: Adviser: Alison Murray
• Keywords: Developmental biology, Physiology
• Date of Award: 1998
• Depositing User: Enlighten Team
• Unique ID: glathesis:1998-75235
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 21:40
• Last Modified: 19 Nov 2019 21:40
• URI: https://theses.gla.ac.uk/id/eprint/75235