Inhibitory effect of glucose and phosphate on the second cleavage division of hamster embryos: is it linked to metabolism?

Hamster embryos cannot complete the second cleavage division in vitro in the presence of glucose and inorganic phosphate (Glu/Pi). Embryos can recover from an 8 h (12:30-20:30 h) exposure to Glu/Pi, although cleavage is retarded by 10 h and continued development to the blastocyst stage is rare (2%). The vulnerability of 2-cell embryos to Glu/Pi changes during the cell cycle, being greatest just prior to cleavage which occurs at approximately 21:00 h: exposure to Glu/Pi from 12:30-14:30 h allowed 94% development to morulae/blastocysts while exposure from 18:30-20:30 h decreased morula/blastocyst development to 48%. This inhibitory effect is also modulated by the length of exposure and energy substrate composition of the culture medium. It is unclear how Glu/Pi interferes with cleavage, but a metabolic explanation is likely because (i) metabolic inhibitors L-glyceraldehyde, iodoacetate and cystamine exacerbated the effect and (ii) the organization of active mitochondria observed with Rhodamine 123 and confocal microscopy is disturbed by Glu/Pi.