Distribution and Sequence of Pyknotic Cells in Rat Fetuses Exposed to Busulfan

Busulfan, an antineoplastic bifunctional-alkylating agent, is known to induce developmental anomalies. In the present study, we examined the distribution and sequence of pyknotic cells in rat fetal tissues exposed to busulfan. Pregnant rats on gestation day 13 were administered intraperitoneally 30 mg/kg of busulfan, and fetal tissues were examined at 6, 12, 24, 36, 48, 72 and 96 hours after treatment (HAT). Pyknosis of component cells was observed markedly in the brain, moderately in the eyes and spinal cord and mildly in the craniofacial tissue, mandible, limb buds, tail bud, ganglions, alimentary tract, lungs, kidneys, pancreas and liver. In the brain, mitotic inhibition was also detected. Most of the pyknotic cells were considered to be apoptotic cells judging from the results of TUNEL staining and electron microscopic examination. Commonly in the above-mentioned tissues, pyknotic cells began to increase at 24 HAT, peaked at 36 or 48 HAT and disappeared at 96 HAT, which is when the histological picture returned to normal in most tissues except for the brain, spinal cord and eyes. The present study clarified the outline of busulfan-induced apoptosis in rat fetuses

Ocular lesions induced in infant rats by busulfan

Although busulfan, a bifunctional alkylating agent, is known to induce cataracts in infant rats, the full nature of busulfan-induced ocular lesions has not yet been shown. In order to clarify this point, 6-day-old rats were treated with a single dose of 20 mg/kg busulfan and the ocular tissue was histopathologically and immunohistochemically examined at 1, 2, 4, 7 and 12 days after treatment (DAT). As a result, in the nuclear layer (NL) of the peripheral retina, apoptotic cells significantly increased at 1 DAT and peaked at 2 DAT when cell proliferating activity was depressed. At 4 DAT, the NL showed wavy deformation with formation of rosette-like structures, and these changes progressed prominently at 12 DAT. In addition, a significant reduction in the retinal thickness due to decreased thickness of NL or inner NL was detected at 2 and 4 DAT. On the other hand, in the germinative zone of the lens equator, apoptotic lens epithelial cells significantly increased from 2 to 7 DAT, resulting in partial loss of lens epithelial cells at 7 and 12 DAT. At 12 DAT, prominent swelling and vacuolation of lens fibers were observed in the area from the equatorial zone to the posterior pole, indicating the development of cataract. The present results strongly suggest that prominent apoptosis in component cells was the initial and essential event underlying the developpment of busulfan-induced ocular lesions in infant rats