RESTORATION OF OOCYTE MATURATIONAL COMPETENCE DURING THE NONBREEDING SEASON WITH FOLLICLE-STIMULATING-HORMONE STIMULATION IN SQUIRREL-MONKEYS (SAIMIRI-BOLIVIENSIS-BOLIVIENSIS)

The in vitro maturation potential of oocytes retrieved during the nonb reeding season with or without prior in vivo low-dose FSH stimulation was studied in adult squirrel monkeys (Saimiri boliviensis boliviensis ). Additionally, the adequacy of various protein supplements in media used for oocyte maturation was investigated. Ovaries were removed from animals in the nonbreeding season (n = 9) with or without prior treat ment with a low dose (I mg) of FSH for four days before ovariectomy. M inimal estradiol elevation was observed in serum even with stimulation . For oocyte collection, ovaries were placed in warmed 21 mM HEPES-buf fered Ham's F-10. Oocytes from unstimulated ovaries were retrieved and cultured (47 of 62 recovered) in bicarbonate-buffered Ham's F-10 medi um containing 0.5% BSA as protein supplement. Negligible maturation wa s observed at 48 h (3 of 47; 6%), and no fertilization was seen after insemination. Immature oocytes from animals stimulated with a low dose of FSH were cultured (69 of 94 recovered). With prior FSH stimulation , oocytes placed in 0.5% BSA medium matured (13 of 24; 54%) and fertil ized (7 of 21; 33%) in marked contrast to oocytes from the nonstimulat ed monkeys. Additionally, 20% monkey serum and 20% human follicular fl uid were studied as alternative protein supplements for the FSH-pretre ated oocytes; these produced similar maturation rates (10 of 22, 45%; 10 of 23, 43%, respectively) and fertilization rates (8 of 21, 38%; 6 of 21, 29%, respectively). In some cases, 2 pronuclei were observed at 16 h and 4 cells were observed at 40 h. Of those activated, 63% showe d cleavage ranging from 2 to 8 cells by 96 h. The results of this stud y in the squirrel monkey indicated that during the nonbreeding season, maturational competency was lost but could be restored by in vivo sti mulation with a low dose of FSH Additionally, the findings show that H am's F-10 supplemented with either 0.5% BSA, 20% monkey serum, or 20% human follicular fluid will support maturation of squirrel monkey oocy tes in vitro once competency has been achieved.