Endocrine Abstracts

Cimetidine is a selective antagonist of histamine at gastric H₂-receptor sites. A 24 month oral cimetidine toxicity and carcinogenicity study in rats at dose levels of 150, 378 and 950 mg/kg was performed. Cimetidine appeared to produce changes involving the liver and the male reproductive organs. In this paper non-tumour Leydig cell morphology was normal in cimetidine treated groups. It was concluded that the higher statistically significant incidence (apparent only in aged rats) of benign Leydig cell tumours seen in cimetidine treated groups compared to controls probably represented a chance occurrence and did not imply a tumorigenic risk for man.