Changes in the activities of hepatic lipogenic-related enzymes and in the concentrations of various plasma and liver lipid fractions in hens before and after the onset of laying.

Abstract

The changes in the concentrations of various plasma and liver lipid fractions, plasma E2 and corticosterone, and hepatic lipogenic related enzyme (LRE) activities, were determined. The relationships between the concentrations of these plasma hormones and hepatic lipoge-nesis around the onset of egg production were elucidated.E2 concentration rose gradually as the hens advanced in age, reaching a peak at the age of 150 days which was the period immediately before the onset of egg laying. Triglyceride, NEFA, total cholesterol and phospholipid levels in the plasma remained relatively constant between 90 and 140 days of age. These rose rapidly as the birds neared the age of 150 days, and reached their peaks immediately before the onset of laying. These values decre-ased, and then remained stable, upon the onset of egg production; nevertheless, even at their reduced levels, they were still comparatively higher than these obtained during the 90-140 days of pre-ovulation period.Hepatic triglyceride content rose gradually and simulataneously with the aging of the hens and reached a peak immediately before the onset of laying. It decreased when the egg laying set in, but remained at a relatively higher level thereafter.The activities of hepatic LREs increased gradually as the hens advanced in age. Fatty acid synthetase reached a peak at 130 days of age and citrate cleavage enzyme and NADP-malate dehydro-genase, 140 days of age.Statistically significant positive correlations were observed between plasma E2 concentra-tion and the grouped parameters of abdominal fat weight (P<0.01), hepatic triglyceride content (P<0.01), concentrations of various plasma lipid fractions (P<0.01), and activities of fatty acid synthetase (P<0.05), NADP-malate dehydrogenase (P<0.05) and citrate cle-avage enzyme (P<0.05) in the liver of hens.