DESATURATION OF STEARATE IS INSUFFICIENT TO INCREASE THE CONCENTRATIONS OF OLEATE IN CULTURED RAT HEPATOCYTES

Desaturation of stearate and palmitate and its effect on cellular accu mulation of oleate were determined in primary culture of rat hepatocyt es. The rate of oleate synthesis as measured by the formation of monou nsaturated fatty acids from stearate was significantly higher than tha t from palmitate. The rate of [1-C-14]stearate incorporation into olea te [1208 +/- 195 pmol/mg protein.4 h)] was 80% higher than that of [1- C-14]palmitate [(672 +/- 82 pmol/(mg protein.4 h)]. Despite the differ ent rates of desaturation, the cellular oleate concentrations did not differ in the cells treated with stearate and palmitate (i.e., 42.5 +/ - 4.5 vs. 40.8 +/- 5.2 nmol/mg protein). On the other hand, oleate con centration in the cells incubated with exogenous oleate was 198.1 +/- 9.5 nmol/mg protein. There was a dose-dependent increase in cellular s tearate concentration by increasing stearate concentrations from 0.5 m mol/L to 4.0 mmol/L in culture medium. A linear increase in cellular s tearate concentration was also achieved by increasing the duration of incubation with 1.0 mmol/L stearate from 2 to 24 h. Despite the marked increases in stearate concentrations under these conditions, oleate. concentrations remained unchanged in the cells. These results do not s upport the contention that the hypocholesterolemic effect of stearate may be mediated by its conversion to oleate, although stearate is a mo re favorable substrate for desaturation than palmitate.