Turnover of Plasma Palmitate in Fed and Fasted Lactating Cows

Abstract

Palmitate-9,10-T was injected intravenously as a single dose into three normal, fed, lactating cows and later into the same cows after they had been carried through a four-day fast. The tritium concentration was measured at frequent intervals in plasma nonesterified fatty acids (NEFA) and in body water. The time course of NEFA specific activity followed a log linear rate during the first 5 to 6 rain, then followed a more complex pattern. The intercept on the :Y axis slope of the initial change in specific activity with time provided the basis for calculating severM kinetic parameters for the NEFA pool. The first component had a space somewhat larger than the plasma volume and a turnover time of 1.9 rain in fed cows, showing that this component is very active metabolically. The turnover time of plasma NEFA was increased to 2.9 rain in fasted cows. Fasting caused a five-to sixfold increase in the concentration of plasma NEFA and a five-to ninefold increase in the pool size. The flux or exchange rate of the NEFA pool increased from 9.2 to 38.5 t~Eq/kg body weight per minute when the lactating cows were deprived of food for four days.