Studies on the effect of oestrogen treatment on the lipid metabolism of the male chick (Gallus domesticus)
The aim of this study was to investigate the early (<48 h) changes in lipid metabolism occuring in the liver after 17B-oestradiol treatment (0.75 mg/100 g body wt.) of the male chick in vivo. An increase in liver weight was observed from 13 - 61 h after oestrogen treatment while an oestrogen-induced increase in the total hepatic DMA content was observed from 37 - 61 h suggesting that the early ( <37 h) liver growth response involved cell hypertrophy where as cell hyperplasia was involved in the later ( <37 h) phase of the response. Oestrogen-induced increases in total liver triacylglycerol and phospholipid were observed from 7 h post-injection while an oestrogen-induced increase in total liver free fatty acid was not observed until after 26 hours. Similarly, total triacylglycerol and phospholipid concentrations in the plasma increased progressively from 7 - 44 h after hormone treatment. Plasma levels of VLDL-triacylglycerol and VLDL-phospho- lipid in similarly-treated birds increased from 13 h and 6 h post- injection, respectively, involving an oestrogen-induced increase in the number of VLDL particles specifically enriched with phospholipid. An oestrogen-induced increase in total free fatty acids in the plasma was not observed at any time post-injection. Analysis of the fatty acid compositions of liver triacylglycerol, VLDL-triacylglycerol and VLDL-phopsholipid, accumulating in oestrogen- treated chicks, revealed that the major oestrogen-induced change was an increase in the level of oleic acid, from 13 hours post-injection. An oestrogen-induced increase in the hepatic activity of the key lipogenic enzyme acetyl-CoA carboxylase (E.C.188.8.131.52) was observed from 24 - 48 h post-injection, involving increased specific activity both with respect to protein and DNA, and total organ activity. The results from the study were correlated in an attempt to determine the early sequence (< 48 h) of oestrogen-induced changes in lipid metabolism.