The present studies were undertaken to examine the time-dose relationships for the induction of lung adenocarcinomas and mammary adenocarcinomas in female BALB/c mice following gamma irradiation. Twelve-week-old female BALB/c/An NBd mice were irradiated with 137Cs gamma rays, and lifetime tumor incidences following high-dose-rate, low-dose-rate, or fractionated exposure regimens were compared. Analysis of the results indicated that the data could be fitted by linear-quadratic dose-response models for the induction of both tumors following acute doses and a linear model with a slope similar to that for the linear portion of the linear quadratic following low-dose-rate exposure regimens. When doses were fractionated the response was dependent upon the dose per fraction. If the dose per fraction was a dose which was predominantly on the linear portion of the acute dose response curve, then the response was linear and similar to that after low-dose-rate exposures. If the dose per fraction was in a region where the quadratic portion of the acute dose-response was significant, then the tumor incidence was higher than that following low-dose-rate exposures.
Butylated hydroxytoluene (BHT) was given in the feed to determine its effect on life span in genetically well-defined, barrier-derived BALB/c mice. Both sexes received 0.75% BHT for three different treatment periods: (A) 8 to 11 weeks of age; (B) for life, beginning at 11 weeks; (C) for life, beginning at 8 weeks of age. The control group (D) was untreated. All BHT treatment groups had mean survival times which exceeded that of controls. The order of survival was B greater than C greater than A greater than D (Males: 890, 832, 726, 684 days; Females: 875, 798, 759, 701 days). Most of the increases in mean survival time were related to a reduction in early deaths (350--600 days) in BHT-treated mice. The reason for the life-lengthening effect on BHT was not identified, but it may relate to alterations in specific disease incidences.
Male and female Syrian golden hamsters were exposed for 2 h once a week for 10 consecutive weeks to 344 mumol/l of 3-methylfuran (3MF), an agent known to produce acute Clara-cell necrosis. Ten months later their respiratory function was evaluated. No functional differences were found between control and treated animals, and histopathologic evaluation of the lungs did not reveal any major treatment-related alterations. Male and female BALB/c mice were exposed for 1 h to 26.8 mumol/l of 3MF once weekly for 10 wk. After 2 yr the tumor incidence in exposed animals was not increased when compared to controls. It is concluded that the acute Clara-cell necrosis produced by 3MF at the doses used is of little long-term consequence.
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