REPRODUCTIVE TOXICITY OF 1,3-BUTADIENE IN THE MOUSE - CYTOGENETIC ANALYSIS OF CHROMOSOME-ABERRATIONS IN FIRST-CLEAVAGE EMBRYOS AND FLOW CYTOMETRIC EVALUATION OF SPERMATOGONIAL CELL-KILLING

Reproductive effects of 1,3 butadiene inhalation have been evaluated i n male mice by reduction of post-meiotic germ cells, alteration of spe rm chromatin structure and transmission of chromosome aberrations to o ne-cell embryos. Animals were exposed for 5 consecutive days for 6 h p er day to butadiene concentrations of 130, 500 or 1300 ppm. The testic ular fraction of post-meiotic germ cells was measured by flow cytometr ic analysis on the basis of their DNA content. Round spermatids were d iscriminated from mature, elongated spermatids by their different degr ee of chromatin condensation. Butadiene-induced cytotoxic effects on d ifferentiating spermatogonia were shown by a concentration-dependent d ecrease of round spermatids occurring 21 days after chemical exposure, confirmed by a similar decrease of elongated spermatids measured in t estes sampled 7 days later. Statistically significant effects were see n already at 130 ppm. An incomplete repopulation of the elongated sper matid compartment observed 35 days after exposure to 1300 ppm suggeste d that, at the highest concentration tested, butadiene toxicity extend ed to stem cells. Alterations of sperm chromatin were revealed by its increased sensitivity to acidic denaturation in situ. The percentage o f abnormal sperm was significantly increased after butadiene exposure of differentiating spermatogonia and spermatocytes. This suggested the induction of persistent effects interfering with chromatin remodellin g during spermiogenesis. Chromosome-type structural aberrations were s ignificantly elevated in first-cleavage embryos conceived by males mat ed during the first and second week after the end of exposure. The low est effective tested concentration was 500 ppm, the same reported for dominant lethal induction under identical exposure conditions. As in t he dominant lethal assay, the effect of this dose was confined to expo sed sperm, while both sperm and late spermatids were affected by the i nhalation of 1300 ppm. A quantitative comparison between the effects i nduced by intraperitoneal injections of diepoxybutane or butadiene inh alations suggested that other reactive intermediates, in addition to d iepoxybutane, might contribute to mediate butadiene-induced reproducti ve toxicity. (C) 1998 Elsevier Science B.V.