THE EFFECT OF COMPOUNDS ALTERING THE CAMP LEVEL ON REVERSING THE 2-CELL BLOCK INDUCED BY HYPOXANTHINE IN MOUSE EMBRYOS IN-VITRO

The possibility of reversing the hypoxanthine induced 2-cell block in mouse embryos when cultured in conditions supplemented with compounds that increase (FSH, hMG, IBMX, hCG) or inhibit (GnRH-analogue) cAMP wa s assessed. When embryos were cultured in Ham's F-10 without hypoxanth ine supplemented with each of the above compounds, no inhibition of bl astocyst development was observed. Embryos were then cultured in Ham's F-10 with hypoxanthine supplemented again with each compound. For the addition of GnRH-analogue or FSH, the rate bf blastocyst formation wa s comparable with that of the control medium with hypoxanthine alone. Instead, the addition of IBMX or hMG reversed the induced block. There was no reversible effect for the addition of 2 mu g/ml hCG while the latter was observed with higher doses. The results from GnRH-analogue and IBMX addition show that, contrary to what was found for oocytes, s timulation of cAMP reverses the hypoxanthine-induced block in mouse em bryos. FSH and hCG also had effects opposite to those observed for ooc ytes. It is unknown why hMG (FSH + LH) reverses the block, A lower cAM P degradation rate resulting in a higher cAMP level is a possible expl anation. Our results provide further evidence that cleavage arrest by hypoxanthine has a different mechanism than the hypoxanthine-induced a rrest of meiosis.