Hepatic secretion and turnover of serum phosphatidylcholine-cholesterol acyltransferase in male and female rats.

The activity of serum phosphatidylcholine-cholesterol acyltransferase (LCAT), output of the enzyme by the perfused rat liver, and the effect of pretreatment with colchicine on LCAT were studied in male and female rats. It was observed that: 1. Serum LCAT activity in the female exceeded that of the male in fasted animals, whereas in fed animals, LCAT activity was higher in the male than the female. With both sexes, however, serum LCAT activity in fed animals was greater than that in fasted animals. Data are presented which suggest that the observed sex differences were due to concentration and/or composition of the substrate rather than to differences in the serum concentration of the enzyme. 2. The release of LCAT by perfused livers from fasted female rats exceeded that of the male animals. The output of LCAT was inhibited by pretreatment (male) with colchicine, which suggests that hepatic secretion of LCAT is dependent on vesicular transport. 3. The decay of serum LCAT activity in vivo following injection of colchicine was more rapid in fasted female rats than in male animals. These observations lead us to postulate that the turnover rate of LCAT is higher in female rats than in male animals.