Inhibition of p-chlorophenoxyisobutyrate by 1-methyl-2-mercaptoimidazole and related compounds

The induction of both rat liver mitochondrial α-glycerophosphate dehydrogenase (GPD) and the soluble malic enzyme by thyroid hormone is enhanced by p-chlorophenoxyisobutyrate (CPIB). CPIB also affects lipid metabolism by a mechanism which is unrelated to the thyroid hormone.The intensification of the T₄ response by CPIB was blocked by the simultaneous administration of the goitrogen, l-methyl-2-mercaptoimidazole (methimazole, MI), and this particular inhibition of CPIB by MI was shared by a number of other compounds containing the ureido or substituted ureido grouping: 1-methylimidazole, imidazole, thiourea, 2-thiouracil, 2-mercaptobenzimidazole, 2-hydroxybenzimidazole and 2- mercaptopyrimidine. However, the effect of CPIB in (a) preventing an orotic acid fatty liver, or (b) intensifying the β-lipoprotein band in serum gel electrophoresis was not inhibited by imidazole.Rat liver malic enzyme activity was increased somewhat by MI and other ureido compounds per se.