GPR31 and metabolic syndrome: In male Ffar4KO mice, ChemR23 expression was lower at baseline, but showed a much larger increase in response to the HFpEF-MetS diet, while GPR31 was elevated regardless of diet in the male Ffar4KO, suggesting a potential link between decreased 18-HEPE levels, increased 12-HETE levels, and macrophage function in male Ffar4KO mice on the HFpEF-MetS diet.