New approaches to mutagenicity studies in animals for carcinogenic and mutagenic agents. I. Modification of the heritable translocation test.

Two alternative modifications of the experimental protocol for the heritable translocation test are described. One of them proposes to mate F1 males and F1 females within one experimental group and eliminate normal pairs by a sequential decision procedure based on litter sizes. Pairs that do not meet the criteria for normal litter size have to be separated and tested against normal partners. Male translocation suspects are analyzed cytogenetically for presence of a reciprocal translocation. Female translocation suspects or XO suspects are verified through analysis of their male and female progeny. The second modification of the heritable translocation test omits fertility testing and proposes to cytogenetically analyze 25 diakineses-metaphases I from each F1 male in the test. Using either one or both protocols it was shown that 20 mg/kg of methyl methanesulfonate (MMS) induced 1.3% heritable translocations in late spermatids and early spermatozoa. With 2.5 mg/kg of mitomycin C, 0.3% and 0.4% translocation carriers were recovered from treated primary spermatocytes and early spermatids, respectively. A dose of 300 R gamma rays resulted in 1.6% translocations in spermatozoa and 4.8% translocations in primary spermatocytes. The advantage of the modified fertility test lies in the doubling of the sample size by including the females. However, a disadvantage is the amount of time and labor that is necessary to verify female translocation carriers. The cytogenetic translocation test protocol with all F1 males is considered more reliable and faster. It lacks the possibility of error entailed in the decision procedure by fertility testing, and it requires less time, personnel, and animal space.