Utilization of intestinal triglyceride-rich lipoproteins in mammary gland of cows

Elution profiles of total lipoproteins, apolipoprotein B (apoB) concentrati ons in lipoproteins, and plasma triglyceride (TG) levels were examined in e arly-, late-, and non-lactating cows. Additionally, arteriovenous (A-V) dif ferences were also measured to elucidate the uptake of TG and apoB-containi ng lipoproteins in mammary gl;and. Non-lactating cows showed three major pe aks corresponding to triglyceride-rich lipoprotein (TRL), low density lipop rotein (LDL), and high density lipoprotein (HDL) fraction, whereas both ear ly- and late-lactating cows revealed two peaks corresponding to TRL and HDL . The peak area of TRL in early- and late- lactating cows were significantl y (p<0.05) smaller than that in non-lactating cows. The plasma TG levels an d apoB-48 concentrations of TRL in early- and late-lactating cows were also significantly (p<0.01) lower. Furthermore, early lactating cows showed sig nificantly (p<0.05) larger A-V differences in both plasma TG and apoB-48 co ncentration of TRL than those in late- and non-lactating cows. These result s suggested that TG in exogenous (intestinal) TRL was utilized for milk fat synthesis in lactating mammary gland of cows by the receptor-mediated upta ke.