The effect of diet on the incidence of pituitary tumours in female Wistar rats

Each of 5 groups of 50 weanling Wistar-derived female rats was fed a different diet ad libitum for 2 years. The diets included 3 commercial maintenance diets (R and M No. 1, R and M No. 491 and RDM 22), a purified or semi-synthetic diet (LJ 80) and the diet (LAD 2) normally used in this laboratory. A weighed amount of LAD 2 diet (less than would be consumed under ad libitum conditions) was fed each day to a 6th group of rats. The survivals of the groups of rats fed either the standard diet (LAD 2) in restricted amount or the maintenance diet (RDM 22) were 62% and 66% respectively and were significantly better than the 40% survival of the group fed LAD 2 ad libitum. The survivals of the groups fed either Rand M No. 491 or LJ 80 were 40-42%, and the group fed Rand M No. 1 had a survival of 52%. At the end of 2 years the 2 groups with the best (>60%) survivals weighed significantly less than the group fed LAD 2 ad libitum. The groups fed either LAD 2 in restricted amount or RDM 22 had the least gross pathological lesions for the majority of the organs. These same groups also had fewer pituitary tumours per group (72% and 66%) than the group fed LAD 2 ad libitum (90%). The group fed RDM 22 also had the largest % (26%) of normal pituitaries of all the groups in the study. There were some significant differences between the haematological and clinical chemistry results of the group fed LAD 2 ad libitum and the other groups but none of the changes was considered adverse, although the groups fed either RDM 22 or Rand M No. 491 had significantly increased mean aminotransferase (AST and ALT) values with large variations which were adjudged undesirable. There was less protein in the urine of the groups fed either RDM 22 or LAD 2 (restricted).