Satosi Kagabu

Histological analysis of the ‘critical point’ in follicular development in mice

AimTo histologically examine ovarian follicular development in cycling mice.MethodsMice were observed at 13:00 h at each stage of the estrous cycle. The ovaries were cut into complete serial sections. All sections were observed, and the size of each follicle was measured by using a micrometer. Follicles with advanced atresia were excluded and non-atretic healthy follicles were differentiated from atretic follicles.ResultsThe measurement of the number of follicles in each stage of the estrous cycle, with reference to their size, showed that in each mouse, the number of small healthy follicles (100–249 μm in average diameter) was approximately 100 for all stages and the number of medium-sized healthy follicles (250–349 μm) was close to 20 in only the metestrus and diestrus stages. In contrast, large healthy follicles (≥350 μm) showed marked changes throughout the estrous stage. Many healthy large follicles were observed in the proestrus stage, but they disappeared in the estrus stage, which suggests that they have ovulated. This was supported by observations of oocytes resuming meiosis in large healthy follicles.ConclusionAs follicular atresia was frequently observed in follicles of 250–399 μm diameter, this size range may be a ‘critical point’ for atresia. The results suggest that there is a ‘critical point’ in follicular development, and that only follicles that pass this point will ovulate, while those that do not will become atretic follicles.

Ovarian follicular development in the unilateral ovariectomized rat

Background and AimsFollowing unilateral ovariectomy, the contralateral ovary underwent hypertrophy and the number of ovulations remained unchanged. The aim of the present study was to elucidate the mechanism, which occurred by this compensation, through examination of ovarian follicular development in operated rats.MethodsRats were examined 1–8 weeks post unilateral operation. The ovaries were serially sectioned. All sections were examined and the size of each follicle was measured.ResultsLarge follicles soon recovered after surgery, but it took 5 weeks for small and medium-sized follicles to recover. The rate of atresia at the ‘critical point’ was 31.1% in unilateral ovariectomized animals and 73.9% in the shamoperated rats.ConclusionsThese findings showed that in operated rats, the recovery of the number of follicles varied depending on the size of the follicle. Compared with the control animals, approximately twice as many large healthy follicles were saved from atresia at the ‘critical point’, producing a compensatory increase in the ovulation number (P< 0.01).

Survival of mouse ovarian tissue transplanted into the uterine horn of post-partum rats nursing pups of various numbers and sizes

Aim and backgroundTo investigate the effect of the number of pups being nursed on the survival of mouse ovarian tissue transplanted into the post-partum rat uterus.MethodsMouse ovarian tissue was transplanted into the uterine horn of post-partum rats. The number of pups nursed by each recipient rat was adjusted in a manner predetermined. Examinations were undertaken at 1–11 weeks after transplantation. Ovarian tissue containing healthy follicles was considered to have taken successfully.ResultsIn rats with 12 pups, ovarian tissue remained viable at 11 weeks post-transplantation. No viable ovarian tissue remained when there were one or two pups. Viability improved as the number of pups increased.ConclusionWhen mouse ovarian tissue is transplanted into post-partum lactating rats, viability improves as the number of pups increases. We concluded that these findings may be explained in terms of progesterone levels in the recipient rats.

Ovarian follicular development in the unilateral ovariectomized rat: Compensatory hypertrophy of the ovary

Background and Aims:  Following unilateral ovariectomy, the contralateral ovary underwent hypertrophy and the number of ovulations remained unchanged. The aim of the present study was to elucidate the mechanism, which occurred by this compensation, through examination of ovarian follicular development in operated rats.