A Preliminary Report on the Effect of Forskolin on the Meiotic Progress of Germ Cells into Prophase I in Fetal Rabbit Ovaries Cultured in vitro

胎齢26日の家兎胎子より卵巣を摘出し、器官培養することによってadenylate-cyclase activatorであるforskolinが減数分裂の開始に影響を及ぼすかどうかについて検討した。金網台-レンズペーパー法を用いて連続12日間、卵巣を器官培養したところ、卵巣表面の結合組織が卵巣を被嚢する状態にまで増殖し、卵巣は扁平化し、組織の崩壊が認められた。卵巣中心部には広範な壊死が見られたが、卵業表層部の組織は健全であり、対照区、forskolin 20μM添加(f20)区および100μM添加(f100)区の全ての区で減数分裂に移行した卵母細胞が観察された。生殖細胞の減数分裂への移行の程度は対照区で4.0%、f20区で21.1%、f100区で9.0%であった。f100区での減数分裂の進行程度は対照区のものと比較してやや早い傾向が認められたものの有意ではなく、f20区で有意に早まった。これらのことから、最適濃度は明確ではないが、forskolinの培養液への添加は生殖細胞の減数分裂開始時期の促進に有効であることが示唆された。

The effects of forskolin, which is an adenylate-cyclase activator, on the progress into meiotic prophase I was investigated in fetal rabbit ovaries of 26 days of gestation, using organ culture (stainless grid-lens paper method, according to Fell and Weiss, 1965) for 12 days. The explanted ovaries became flattened in their macroscopic shape, and necrosis in the deeper parts of the ovarian tissue was recognized in histology, caused by adhesion to the lens-paper, with the extra-ovarian connective tissue proliferating into the basic medium. In order to estimate the degree of progress into meiotic prophase I, the percentages of oogonia (mitotic and resting stage) and oocytes (leptotene, zygotene, pachytene and diplotene) were compared for all germ cells counted in 3 groups of organ cultures-0 μM (control), 20 μM (f20) and 100 μM (f100) forskolin. Although oocytes in diplotene were never observed, germ cells transforming into oocytes were recognized in all explanted ovaries of each group, except for the control, in which no oocytes in pachytene were found. According to the comparisons of the ratio of total oocytes to all germ cells counted in control (4.0%), f20 group (21.1%) and f100 group (9.0%), the degree of progress of meiotic prophase I in f100 group was not significantly different from that in control, although the degree of progress was somewhat higher. On the other hand, the degree of progress in f20 group was significantly higher than in control (p <0.01). It is suggested that the addition of forskolin to the basic medium of organ culture is effective in promoting progress into meiotic prophase I.