Injection of goldthioglucose (GTG) destroys the bilateral ventro-medial nucleus, the “satiety area” and gives rise to hypothalamic obesity in mice (abbreated later as GTG mice).
A considerable number of papers have been published on lipid metabolism of liver and adipose tissue in these obese animal. However, little is known about individual fatty acids synthesis in GTG mice.
In this report, the author disclosed the individual fatty acids synthesis of liver and adipose tissue in GTG mice.
Observations were performed both in vitro and in vivo, with analysis of the incorporation and distribution of 1-¹⁴C-acetate in individual fatty acids of major lipid classes
Results were as follows.
Experiment on liver;
1) Liver of GTG mice incorporated significantly more 1-¹⁴C-acetate in saponifiable fraction of lipids (=total fatty acids) than liver of control mice did.
2) In regard to the study on the distribution of 1-¹⁴C-acetate in individual fatty acids separated by gaschromatography, the percentage of radioactivity recovered in oleic acid significantly increased in GTG mice. On the other hand, the percentage of radioactivity in fatty acids with retention time corresponding to arachidic acid or longer relatively decreased.
3) After four hours' incubation of liver with 1-¹⁴C-acetate in vitro, the percentage distribution of radioactivity recovered in triglyceride significantly increased in GTG mice compared with control mice.
In vivo, the percentage distribution of radioactivity increased in liver triglyceride with time from one hour to four hours after administration of 1-¹⁴C-acetate in GTG mice.
4) It is conspicuous that the amount of radioactivity recovered in oleic acid of GTG mice was always significantly higher than in that of control mice, on analysis of ¹⁴C distribution in individual fatty acids esterified into triglyceride, both in vitro and in vivo.
The percentage distribution of ¹⁴C in oleic acid of triglyceride in GTG mice was increasing with time up to four hours in vivo, too.
5) In individual fatty acids esterified into phospholipids, the percentage of ¹⁴C found in oleic acid of GTG mice was also higher than in that of control mice.
6) In vitro, fasted animals incorporated less ¹⁴C into total fatty acids than fed animals in both GTG and control mice and significant decrease was observed in the percentage of ¹⁴C in myristic acid and palmitic acid.
Experiment on adipose tissue;
There was a highly significant increase in the incorporation of ¹⁴C into total fatty acids in the tissue of GTG mice compared with control mice.
However, no significant differences were found in the percentage distribution of ¹⁴C in major lipid classes nor in individual fatty acids of saponifiable fraction of lipids between both groups of mice.
From these results, the author advocates a possibility that obesity of these animals is due to the increased synthesis of fatty acids and incresed accumulation of triglyceride esterified with oleic acid.