Lecithin:cholesterol acyltransferase (LCAT) activity in serum was evaluated in spontaneous cases of fatty liver in cows. The enzyme activity of 631 +/- 62 U (mean +/- SEM, decrease in nmol of free cholesterol per h per ml of serum) in cows with fatty liver (n = 16) was significantly (p < 0.01) lower than that in cows without fatty liver (979 +/- 22 U; n = 16). In addition to the decrease in LCAT activity, the concentrations of phosphatidylcholine (a fatty aryl donor for esterification of free cholesterol) and of cholesteryl esters (products of the LCAT reaction) were reduced in the high-density lipoprotein fractions from cows with fatty livers. The concentrations in the serum of apolipoprotein A-I, an activator of LCAT, was also reduced in cows with fatty livers. These results suggest that the decreased LCAT activity, which may be attributable to impaired hepatic secretion or to the suppression of the activity in the plasma by reduced concentrations of phosphatidylcholine and apolipoprotein A-I, resulted in the lower concentrations of cholesteryl esters. Because cholesteryl esters are utilized in steroidogenic tissues for the synthesis of steroid hormones such as progesterone and glucocorticoids, and insufficient supply of the cholesterols may be of relevance to the reduced fertility and immune competence observed in cows with fatty livers.

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ABSTRACT. Reduced feed intake near parturition is suggested to be one of the major causal factors for the development of fatty liver in cows, and nonfeeding has been used as an experimental model for fatty liver. In cows with fatty liver, concentrations of lipoprotein lipids and proteins are decreased. In addition, the acute-phase protein haptoglobin is induced. The purpose of the present study was to examine whether the decrease of lipoprotein concentrations and the induction of acute-phase proteins were similarly reproduced by nonfeeding. Holstein female calves (n=5) were nonfed for 3 days and thereafter refed. Serum concentrations of nonesterified fatty acids and β-hydroxybutyric acid were initially increased by the nonfeeding, and followed by decreases in concentrations of cholesteryl esters, phospholipids, apolipoprotein (apo) B-100 and apoA-I. The apoC-III concentration was not distinctly decreased. Haptoglobin and serum amyloid A were induced during the nonfeeding and refeeding process. Haptoglobin was distributed in different proportions in the highdensity lipoprotein, very high-density lipoprotein and the lipoprotein-deficient fractions, whereas almost all serum amyloid A was associated with the high-density lipoprotein fraction. These results suggest that the decreases in lipoprotein concentrations and induction of acute-phase proteins found in cows with fatty liver and those with fatty liver-related diseases such as ketosis are primarily due to the reduced feed intake near parturition. KEY WORDS: apolipoprotein, bovine, haptoglobin, nonfeeding, serum amyloid A.

ABSTRACT. Paraoxonase 1 (PON1) is an enzyme associated with high-density lipoprotein (HDL) and has a protective effect against oxidation of lipoproteins in mammals. We investigated PON1 enzyme activities in bovine serum and its distribution among bovine serum lipoproteins. Paraoxonase activity and arylesterase activity in serum (152 Holstein cows and 42 Japanese Blacks) were 275 ± 55 U/ml and 130 ± 27 U/ml (mean ± SD), respectively. There was a high correlation (r=0.962) between the two enzyme activities, and the activity ratio of paraoxonase/arylesterase did not exhibit individual variation. More than 85% of both paraoxonase and arylesterase activities were detected in the HDL fraction separated by ultracentrifugation. The 43-kDa protein in the HDL fraction was identified as bovine PON1 by N-terminal amino acid sequence analysis. Bovine PON1 was purified by ultracentrifugation and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and an anti-bovine PON1 antiserum was developed. The concentration of PON1 protein determined by immunoblotting was closely correlated (r=0.976) with paraoxonase activity in serum. Bovine HDL was further fractionated into subpopulations, and the distribution of PON1 was examined. Paraoxonase activity and PON1 protein increased with decreasing HDL size and approximately 60% of total paraoxonase activity was distributed in the heavy HDL fraction. The different distributions of PON1 among HDL subpopulations might be concerned to the function and metabolism of bovine HDL. KEY WORDS: arylesterase, cattle, high-density lipoprotein, paraoxonase.

A calf having extremely high concentrations of triglycerides, cholesterol and phospholipids, in particular in chylomicrons (CM) and very low-density lipoprotein (VLDL) fraction was found. The purpose of the present study was to determine serum concentration and distribution of apolipoprotein (apo) C-III, a low molecular mass protein mainly distributed in high-density lipoprotein (HDL) fraction in normolipidemic cattle, in the calf with hyperlipidemia. The serum apoC-III concentration in the calf increased to more than 10-fold that of normolipidemic control calves, and apoC-III was distributed more in the CM than in the HDL. The concentration of apoA-I (a predominant apoprotein in the HDL) was also increased to nearly 4-fold that of controls in the serum from the calf, and its major distribution site was the CM. Haptoglobin was detected in the serum from the hyperlipidemic calf, and was distributed in the CM as well as in the HDL. Serum amyloid A was also induced. In contrast to apoC-III, apoA-I and haptoglobin, the majority of apoSAA was found in the HDL fraction, as observed in normolipidemic calves. Increased concentrations in the CM of apoC-III and apoA-I suggest that the two apolipoproteins may be involved in the pathogenesis of calf hyperlipidemia. The presence of haptoglobin in the CM and HDL also implies the relevance of this acute-phase protein in the regulation of lipid metabolism.