NUTRITIONAL REGULATION OF LIPID METABOLISM IN RATS

IV. METABOLISM OF HEPATIC GLYCEROLIPIDS IN FASTED RATS IN VIVO AND IN VITRO

Abstract

Male Wistar rats fed on a laboratory ration were fasted starting at 6 p. m., and the incorporation of the acyl molecules and acetate into glycerolipids was compared with that of fed rats.
1. The incorporation of ¹⁴C-palmitate and linoleate into hepatic glycerolipids at 0.5 to 6 hr after their injection intraperitoneally into rats that had been fasted for 15 hr was markedly depressed by fasting, whereas there was no remarkable difference in the incorporation of ¹⁴C-stearate. The fractional disappearance rate of ¹⁴C-linoleate from phosphatidylcholine (PC) and phosphatidylethanolamine and that of ¹⁴C-palmitate from triglyceride were greater in fasted than in fed rats. The incorporation of ¹⁴C-palmitate and stearate into the molecular species of PC was specifically altered. Desaturation by the liver of these precursors was depressed by fasting.
2. The synthesis by the liver slices of the acyl moieties from acetate was depressed by fasting.
3. When ¹⁴C-acetate was injected intraperitoneally at the beginning of fasting, the turnover of the labelled fatty acids in the liver between 3 and 6 hr after the injection was slower in fasted rats, that of the polyunsaturated acids being the slowest.
4. These results suggest that the specific changes in the turnover of individual fatty acids in hepatic glycerolipids are principal determinants of fasting-induced changes in the fatty acid compositions.