Utilization of free fatty acids by starved and pregnant sheep.

1. The rate of entry into the plasma of stearic acid in fed and starved non-pregnant sheep and of palmitic acid in fed and starved pregnant sheep has been measured by a continuous-infusion isotope-dilution method. 2. In non-pregnant sheep the entry rate of stearic acid rose from 0.38mg./min./kg. when fed to 0.69mg./min./kg. after 72hr. starvation. In pregnant sheep, the entry rate of palmitic acid rose from 0.55mg./min./kg. when fed to 0.64mg./min./kg. on starvation. 3. The entry rates of palmitic acid and stearic acid are related to their respective plasma concentrations. 4. At a given plasma concentration the entry rate of palmitic acid in pregnant sheep was greater than that of stearic acid in non-pregnant sheep. 5. There was no detectable conversion of palmitate or stearate into other plasma long-chain fatty acids. There was negligible incorporation of fatty acids into other plasma lipids with the exception of the plasma triglycerides of fed pregnant sheep. 6. Up to 12% of expired carbon dioxide was derived from palmitic acid or stearic acid. The high rate of oxidation of plasma palmitic acid in fed pregnant sheep is noteworthy.