AGING CHANGES IN THE ALIGNMENT OF CHROMOSOMES AFTER HUMAN CHORIONIC-GONADOTROPIN STIMULATION MAY BE A POSSIBLE CAUSE OF DECREASED FERTILITYIN MICE

The relation between the alignment of chromosomes in the aged oocyte a nd its capacities of fertilization and development of oocytes was exam ined. More embryos in the condition of insemination at 12 and 16 h aft er human chorionic gonadotropin (hCG) however grew into two and more c ell stages than those in the insemination of 20, 24 and 28 h. Some emb ryos in the group of insemination at 12, 16 and 20 h after hCG injecti on had grown into the blastocyst stage. The embryos inseminated 24 h a fter hCG and later had shown no further development. Twelve hours afte r hCG injection, 67% of oocytes have chromosomes on a straight line (A ), and 29% have chromosomes scattered in one group (B). Three percent of oocytes have them separated toward both spindle ends (C) and 2% of oocytes have no chromosomes (D). At 16 h after hCG, the alignments of chromosomes are almost the same as that of 12 h after hCG injection. A t 20 h after hCG, the most common alignment of chromosomes was scatter ed in a small group. The alignment of chromosomes of most oocytes was splitting at 24 and 28 h after hCG injection. Thus the oocytes with th e chromosome alignment of A or B can be fertilized and developed into the blastocyst stage. The alignment of A and B lasts only about 8 h af ter ovulation. and the time was extremly restricted for oocytes to dev elop normally.