Melphalan, a second chemical for which specific-locus mutation induction in the mouse is maximum in early spermatids.
Melphalan (MLP), a bifunctional alkylating agent structurally related to the highly mutagenic chemical chlorambucil (CHL), was found to induce high frequencies of specific-locus mutations in postspermatogonial germ cells of the mouse, and to be one of only a few chemicals that is also mutagenic in spermatogonial stem cells. Productivity patterns following MLP exposures resembled those that had been found for CHL. Mutation rates in successive male germ-cell stages were measured at three MLP-exposure levels in a total of 95,375 offspring. While the induced (experimental minus historical-control) mutation rate is relatively low in stem-cell spermatogonia (1.2 x 10(-5) per locus at a weighted-mean exposure of 7.3 mg/kg), it is about 5 times higher in poststem-cell stages overall, and peaks at 26.7 x 10(-5) per locus in early spermatids at a weighted-mean exposure of only 5.7 mg/kg. This "type-2 pattern" of mutation yield (Russell et al., 1990), i.e., peak sensitivity in early spermatids, has heretofore been found for only one other chemical, CHL. Mutation-rate data earlier reported for CHL (Russell et al., 1989) were augmented in the present study for comparison with MLP-induced rates. Because of the greater toxicity of MLP, average exposures used for this chemical were only about one-half of those for CHL. When MLP and CHL mutation rates are extrapolated to equimolar doses, they appear very similar for poststem-cell stages overall. However, in the case of CHL, a somewhat higher proportion of the mutations is induced in early spermatids than in the case of MLP.
Russell
L B
LB
Biology Division, Oak Ridge National Laboratory, TN 37831-8077.
Hunsicker
P R
PR
Shelby
M D
MD
D000818:Animals; D002699:Chlorambucil / Q000633:toxicity; D005260:Female; D005298:Fertility / Q000187:drug effects; D007274:Injections, Intraperitoneal; D008297:Male; D008558:Melphalan / Q000008:administration & dosage / Q000633:toxicity*; D051379:Mice; D008809:Mice, Inbred C3H; D009152:Mutagenicity Tests; D009153:Mutagens / Q000008:administration & dosage / Q000633:toxicity*; D013087:Spermatids / Q000166:cytology / Q000187:drug effects*; D016019:Survival Analysis
D009153:Mutagens; D002699:Chlorambucil; D008558:Melphalan