The Effect of Unilateral Ovariectomy in the Neonatal Mouse on Follicular Development

SUMMARY The remaining ovary of a 14-day-old mouse after unilateral ovariectomy (ULO) on day 2 showed the same number and stages of follicles as an ovary in an intact animal of the same age. No increase in the number of developing follicles nor development to more advanced stages occurred. Hemispaying in the neonatal period did not alter the number of follicles that started growth nor their speed of development in the subsequent 12 days. However, premature follicle fluid accumulation and a widening of the theca layer in early growing follicles were characteristically found in the remaining ovary. The failure of the remaining ovary to increase its complement of large follicles is probably due to the fact that those follicle stages (i.e. large follicles) which are able to react to stimulation by follicle-stimulating hormone in the prepubertal and adult ovary are as yet lacking in the early infant ovary. However, reaction to luteinizing hormone can already be expressed and is shown by premature follicle fluid accumulation and widening of the theca layer. The changes seen are interpreted as a reaction of the remaining ovary to a relative increase in an unchanged amount of available gonadotrophin rather than to a change in the pituitary—gonadal feedback mechanism.