THE PATTERN OF APOLIPOPROTEIN B100 CONTAINING LIPOPROTEIN SUBCLASSES PRODUCED BY THE ISOLATED VISCERAL RAT YOLK-SAC DEPENDS ON DEVELOPMENTAL STAGE AND FATTY-ACID AVAILABILITY

Explants of visceral rat yolk sacs from gestational days 16, 18 and 22 , were used for studying developmental changes of secretion and densit y distribution of lipoproteins, particularly of those containing apoB, Moreover, the influence of fatty acid supply on the amount and densit y distribution of secreted apolipoproteins was studied on day 18 of ge station. Active lipoprotein production was observed in yolk sacs taken on days 16 and 18 of gestation. It declined considerably on day 22 of gestation in parallel with the production of total protein, triacylgl ycerols and cholesterol. On all gestational days, apoB floated mainly in the LDL range (greater than or equal to 70%) with differences in th e distribution pattern of LDL subclasses. The lowest density of secret ed LDL was found on day 18 of gestation (peak at d = 1.025 g/ml) follo wed by day 16 (peak at d = 1.035 g/ml) and day 22 of gestation (peak a t d = 1.045 g/ml). ApoAIV, apoE and apoAI floated exclusively in the H DL range with a peak at d = 1.089 g/ml independently of the gestationa l day. After incubation of yolk sacs from the 18th day of gestation wi th 0.4 mM or 0.8 mM oleate, the density of secreted apoB containing pa rticles was decreased (peaks in the VLDL and IDL density range), where as palmitate in the same concentrations caused a redistribution of sec reted apoB toward higher densities (peaks at d greater than or equal t o 1.032 g/ml). Taken together, the data provide evidence that the dens ity of LDL subclasses produced by isolated yolk sacs between days 16 a nd 22 of gestation depended on the gestational stage. Moreover, additi on of unsaturated or saturated fatty acids to the organ culture differ ently affected the secretory rate and the density of lipoproteins deli vered by yolk sacs on day 18 of gestation.