Mercaptoacetate's feeding stimulatory effect is not increased in rats fed a medium-chain triglyceride-rich diet.

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Intraperitoneal (ip) injection of mercaptoacetate (MA) inhibits hepatic fatty acid oxidation (FAO) and stimulates feeding in rats fed diets containing substantial amounts of lipid. Because it remains unclear if the reduction in hepatic FAO causes the increase in feeding, we compared the effects of MA (45.6 mg/kg BW; injected ip at light onset) vs. saline control in rats adapted to diets containing 18% either predominately long-chain (about 95% 16 C and more) or medium-chain (about 70% 10C–14C) fatty acid triglycerides (LCT and MCT, respectively). If MA's feeding stimulatory effect depends on FAO, MA should stimulate feeding more in MCT-fed rats because medium-chain fatty acids are oxidized faster than long-chain fatty acids. To assess) possible metabolic effects of the diets and of MA, rats were killed 30 min after light-onset injections for blood and tissue (liver, duodenum) samples. Relative concentrations of fatty acids in the duodenal tissue matched the patterns in the diets fed. Two results suggested that hepatic FAO proceeded more rapidly in MCT-fed rats. First, plasma β-hydroxybutyrate levels were higher in MCT—than in LCT-fed rats. Second, the relative hepatic content of fatty acids in the liver compared to the diet was reduced more for medium-chain fatty acids than for long-chain fatty acids. Contrary to our hypothesis, however, MA increased 1-h food intake more in LCT than MCT-fed rats (290% vs. 54%, p