A comparison of life-span and spontaneous tumor incidence of male and female Han:WIST virgin and retired breeder rats

In a long-term study, the life-expectancy of 320 female virgin Han:WIST rats was significantly lower than that of 320 male virgins, whereas no major differences existed in a successive study with retired breeders (296 females and 252 males) of the same stock. Within the sexes, the female retired breeders lived on average longer than the virgins, whereas the male retired breeders had a higher mortality between the 33rd and 36th month than their virgin counterparts. Differences in life-expectancy were mainly due to varying incidences of uterine adenocarcinomas in the females and an adverse development of pituitary gland tumors in the males. A sexual difference was found in both groups for tumors of the pituitary gland, the islet cells of the pancreas, mammary gland, subcutis and mesenteric lymph nodes. A possible hormonal influence on tumorigenesis is discussed.