By using a continuous-flow centrifuge to separate carotid artery blood into cells and plasma, sodium linoleate was infused into the jugular vein of five conscious dogs at a mean rate of 41.9 μEq. · kg.−1 · min−1 for ninety minutes without adverse side effects. Linoleate infusion quickly elevated plasma free fatty acid (FFA) levels to approximately 1.50 μEq./ml. and was accompanied by a rapid four- to sixfold increase in plasma immunoreactive insulin (IRI) which was sustained throughout the infusion. After thirty minutes of infusion, plasma glucose began to fall, ultimately declining 35 per cent from control levels. Plasma ketone levels rose to twice their control levels during linoleate infusion but were always less than 20 per cent of the ketone levels shown to be insulinogenic in dogs. Upon termination of the infusion, plasma FFA, IRI, and ketones fell quickly to control levels, while plasma glucose rose toward normal.
The half-life of plasma linoleate, estimated from the infusion rate and the increment in plasma FFA during steady-state infusion, was 0.76 minute. This result, based on net flux, validates estimates based on tracer experiments.
The similarity between the metabolic responses to linoleate infusion and those previously found to oleate suggests that these effects may be common to most physiologic long-chain FFA. Stimulation of insulin secretion by high levels of FFA could thus play a role in modulating lipolytic responses and changes in glucose metabolism accompanying such responses.