Proliferative lesions of the testis in ad libitum-fed and food-restricted Fischer-344 and FBNF1 rats

The effect of 40% food restriction on spontaneous proliferative lesions of the testis was evaluated in lifetime and cross-sectional (serial sacrifice) studies of 419 Fischer (F-344) and 304 Fischer x Brown Norway (FBNF1) male rats. Interstitial cell hyperplasia and interstitial cell adenoma (ICA) were the most common proliferative lesions in each genotype; incidence of each was less in the FBNF1. In each genotype, food restriction delayed the onset of both lesions and reduced the incidence of ICA. At 12 months interstitial cell hyperplasia was present in 11 of 12 ad libitum (AL)-fed and 0 of 12 food-restricted (FR) F-344 rats. In FBNF1 rats interstitial cell hyperplasia was observed first at 18 months in AL-fed and at 36 months in FR groups. Interstitial cell adenoma developed in 5 of 12 AL-fed F-344 rats by 18 months and in 2 of 12 FR rats by 24 months; 2 of 12 AL-fed FBNF1 rats had ICA at 30 months, and 1 of 12 FR rats had ICA at 42 months. In these cross-sectional studies approximately half the ICA cases in F-344 rats were bilateral; no FBNF1 rats had bilateral ICA. In lifetime studies the incidence of ICA was reduced from 49% in AL-fed rats to 19% in FR F-344 rats and from 9% in AL to 4% in FR FBNF1 rats. The incidence of mesothelioma was low in both genotypes and was not obviously altered by food restriction. A malignant embryonal neoplasm, an unclassified benign neoplasm, and three seminomas were present in the testes of FBNF1 rats.