RELATIONSHIP BETWEEN HEPATIC FATTY-ACID DESATURATION AND LIPID SECRETION IN THE ESTROGENIZED CHICKEN

Desaturation of fatty acids is thought to facilitate their incorporati on into glyceride and their subsequent secretion as lipoproteins. Howe ver, in the laying hen, the dramatic increase in hepatic lipogenesis i s often paralleled by a liver steatosis that may affect egg production and even result in death. The balance between lipid secretion and sto rage, in relation to the fatty acid desaturation process, was therefor e investigated in young male estrogenized chickens. Estrogen stimulati on resulted in a dramatic increase in VLDL concentration (40.4 mg/ml v ersus 0.158 mg/ml in control) and hepatic lipid content (8.61 g/liver versus 1.47 g/liver in control). In estrogenized chickens, VLDL, total liver, and microsomes contained relatively more monounsaturated and l ess saturated and polyunsaturated. fatty acids, whereas hepatic Delta 9 desaturase activity was twofold. higher. Moreover, in these birds, t he proportion of monoenoic fatty acids was greater in VLDL (55%) than in the liver (50%), which was indicative oi their preferential secreti on. Therefore, under the influence of estrogen, fatty acid synthesis a nd desaturation are associated with an increased VLDL secretion, which limits the degree of hepatic accumulation of triglyceride and the ris k of subsequent steatosis.