EFFECTS OF LITHIUM-CHLORIDE ON RABBIT BLASTOCYST EXPANSION, AND ACCUMULATION OF PHOSPHOINOSITIDES AND INOSITOL PHOSPHATES

The effects of lithium, an inhibitor of the recycling of inositol in t he phosphatidylinositol cycle, on rabbit blastocyst growth and metabol ism of phosphoinositides were investigated. Day 2 rabbit morulae were first cultured for 2 days in basic culture medium and then transferred to medium containing myo-[2-H-3]inositol for culture for a further 3 days. At the end of culture, the resulting blastocysts were incubated with LiCl (0, 1, 5, 10, 20 mmol l(-1)) for 1h. The blastocysts were th en lysed and both the aqueous and lipid portions were analysed for inc orporated radioactivity. Thin layer chromatographic separation of the lipid portion indicated that lithium had no significant effect on form ation of radiolabelled phosphoinositides. However, high performance an ion exchange chromatography indicated that lithium significantly stimu lated accumulation of radiolabelled inositol monophosphate and inosito l 1,4,5-trisphosphate, This result indicates that the phosphatidylinos itol cycle is turning over in rabbit blastocysts. Continuous culture o f rabbit embryos for 5 days in media containing LiCl (5, 10, 15 and 20 mmol l(-1)) significantly decreased blastocyst growth as measured by blastocyst expansion and incorporation of [H-3]thymidine. However, sup plementing the medium with excess inositol (up to 9375 mu mol l(-1)), in an attempt to increase the intracellular uptake of inositol and thu s compensate for the inhibitory effect of lithium on inositol recyclin g, did not reverse the inhibitory effect of lithium on blastocyst grow th.