Overfeeding increases very low density lipoprotein diameter and causes the appearance of a unique lipoprotein particle in association with failed yo 1 k deposition ’

Structurally specific very low density lipoprotein (VLDL) particles are presumed to redirect VLDL uptake during yolk deposition. Egg production is an energy intensive process, but energy excess negatively affects egg production. This study sought to determine whether overfeeding changed hen lipoprotein profiles, and if so, whether changes were related to egg production. Overfeeding caused 33% of hens to stop yolk deposition and reabsorb unovulated follicles (involute). VLDL of control hens possessed characteristic small particle size (30 nm) and composition indicative of limited intravascular metabolism. Overfeeding generally increased VLDL diameter, the effect being slight (+6.6 nm) in overfed laying hens when compared to overfed-involuted hens (+51.2 nm). Changes in composition indicated that increased intravascular metabolism of VLDL parallelled increases in particle diameter. Overfedinvoluted hens showed significant elevations of plasma low density lipoprotein, VLDL cholesteryl ester, and high density lipoprotein (HDL) triacylglycerol content. Overfeeding increased plasma HDL, and in association with involution, caused redistribution of HDL particle sizes, including the appearance of novel HDL -20 nm in diameter, termed HDLR, and a 97 kDa protein within the HDL fraction. The overfed hen model may provide new insight into the role of lipoprotein physical properties in determining the metabolism of triacylglycerolrich lipoprotein, and the process of reverse lipid transport. Overfeeding generally increases VLDL size and plasma HDL levels suggesting that increased peripheral metabolism, and perhaps mechanical exclusion of enlarged VLDL by the granulosa basal lamina, contribute to the obesity and impaired yolk deposition observed in hens with excessive energy intakes. Temporal definition of massive VLDL enlargement relative to follicular collapse remains to be established. Cessation of yolk deposition accompanied by reabsorption of partially developed follicles appears to be associated with specific redistributions of HDL subpopulations and appearance of HDLR. -walzem, R. L., P. A. Davis, and R. J. Hansen. Overfeeding increases very low density lipoprotein diameter and causes the appearance of a unique lipoprotein particle in association with failed yolk deposition. J. Lipid Res. 1994. 35: 1354-1366. Supplementary key words sition * lipoprotein sizes * reverse lipid transport plasma lipoproteins lipoprotein compoStrategies used by various species to control the metabolism of plasma triglyceride-rich lipoproteins comprise a n area of intense scientific interest. Of particular interest are those factors a n d processes that control the conversion of very low density lipoprotein (VLDL) to intermediate density lipoprotein (IDL), and ultimately low density lipoprotein (LDL). The laying hen provides a unique model for studies investigating the role of lipoprotein physical properties in directing the metabolism a n d resultant tissue partitioning of triglyceride secreted by the liver. Dramatic alterations occur in the levels and physical properties of hepatic lipoproteins in plasma of hens with the onset of egg production (1-7). D u r i n g this same period, the flow of triglyceride from liver to peripheral tissues such as muscle and adipose is largely redirected to yolk. Yolk deposition is a receptormediated event in which VLDL are transported intact from plasma into the developing oocyte (8). The VLDL deposited into yolk are rich in triglyceride (E) in ’ comparison to VLDL of non-laying chickens (4), and the physical modifications of this particle shield it from peripheral hydrolysis and ensure that sufficient TG-energy is deposited into yolk to support embryogenesis (9, 10). Abbreviations: VLDL, very low density lipoprotein; HDL, high density lipoprotein; LDL, low density lipoprotein; IDL, intermediate density lipoprotein; apo, apolipoprotein; LPL, lipoprotein lipase; FLHS, fatty liver hemorrhagic syndrome; SCWL, single comb white leghorn; TG, triacylglycerol; UC, unesterified cholesterol; CE, cholesteryl ester; PL, phospholipid; PRO, protein; GGE, gradient gel electrophoresis; CBR-250, Coomassie Brilliant Blue R-250; SDS, sodium dodecyl sulfate. ‘A preliminary report of the data was made at the 39th Western Poultry Disease Conference, March 4-6, 1990, Sacramento, CA. 2To whom correspondence should be addressed. 1354 Journal of Lipid Research Volume 35, 1994 by gest, on D ecem er 8, 2017 w w w .j.org D ow nladed fom Food intake increases markedly to support the energy and protein requirements of egg production (11). Among “egg-type” hens, such as Single Comb White Leghorns (SCWL), energy intake is apparently driven by egg production, and the relationship between these two parameters can be described mathematically (12). Among chickens selected for rapid body growth, so called “meattype” or broiler birds, tight linkage between food intake and egg production does not occur. Egg production among broiler hens is usually poor (13) and is improved by feed restriction (13, 14). Overfeeding of egg-type chickens is known to variably suppress egg production (15-18). Energy excess is also cited in the etiology of fatty liver hemorrhagic syndrome (FLHS), a spontaneous pathologic condition that can reduce egg production in commercial flocks (18-20). It is unclear why excess energy intake should impair egg production, but untoward effects could be mediated by altered lipoprotein metabolism. Obesity is apparent in most poorly laying broiler breeder hens and hens with FLHS, suggesting that hepatic lipoprotein is ineffectively directed to yolk. To investigate these possibilities, lipoprotein profiles of SCWL hens with a genetic predisposition for high rates of egg production were examined during periods of both normal and excessive energy intake.