13-week subchronic oral toxicity study of isopropyl p-hydroxybenzoate in F344 rats

A 13-week subchronic oral toxicity study of isopropyl p-hydroxybenzoate was performed in both sexes of F344 rats. CRF-1 diet containing 0, 0.25, 1.25, 2.5 or 5% isopropyl p-hydroxybenzoate was fed to 5 randomly constituted groups of animals, each consisting of 10 males and 10 females, to determine appropriate dose levels for a subsequent 2-year carcinogenicity study. No animals died during the administration period. Significant suppression of body weight gain was observed in males of the 2.5% and 5% isopropyl p-hydroxybenzoate groups, and in females of the groups treated with 1.25% or above as compared with the control group. Serum biochemistry evaluations revealed increases in gamma-GTP and total cholesterol in male groups treated with 2.5% or more and increases in gamma-GTP, ALP and BUN in female groups treated with 1.25% or more, as compared to the controls. Histopathologically, centrilobular hepatocellular swelling was observed in males treated with 2.5% or more and in females of the 5% group. In the affected populations, hepatocytes filled with small vacuoles, possibly of lipid native, were sometimes found. An increased severity of intracytoplasmic eosinophilic globule formation in the renal proximal tubular epithelia of males of the 5% group was noted. Based on these results, a dietary concentration of 1% in males or 0.5% in females was concluded to be a suitable maximum tolerable dose (MTD) of this chemical for a 2-year carcinogenicity study in rats.