Influence of visible light and room temperature on cell proliferation in preimplantation rabbit embryos

During in-vitro culture rabbit early cleavage stages (Day 1 p.c.) and compacted morulae (Day 3 p.c.) were exposed to visible light or to room temperature (23 degrees C) for various lengths of time (0.5-24 h). The light source used resembled closely routine laboratory lighting. Controls were cultured simultaneously for 24 h under standard conditions (37 degrees C, darkness). Development was assessed by incorporation of tritiated thymidine as an indicator of cell proliferation. In comparison to non-exposed controls cell proliferation of Day-1 embryos was more impaired by light than by room temperature whereas in Day-3 embryos thymidine incorporation was more reduced following exposure to room temperature than to light. No statistically significant decrease in thymidine incorporation was detectable up to 1 h (light) and 8 h (room temperature) in Day-1 embryos. Morulae tolerated room temperature and visible light for up to 3 h and 8 h, respectively. Split-dose exposure (e.g. 4 x 1 h) to visible light or room temperature revealed no statistically significant differences compared with one long en-bloc exposure (e.g. 1 x 4 h). These results demonstrate a stage-dependent susceptibility of preimplantation embryos to physical environmental factors. The major risk, indicated by the shortest tolerance times, was provoked by visible light to early cleavage stages.