Age-Related Changes of Genital Systems in the Female Crj : CD (SD) IGS Rats during Sexual Maturation

The age-related changes of vaginal opening, body weight, the weights of the uterus and ovary, together with histological examination, serum 17β-estradiol (E2) and progesterone levels were examined in intact female Crj:CD[○!R] (SD) IGS rats between 21 and 36 days of age to understand the basic biological profile of changes of the female genital system during sexual maturation in the rat for female pubertal assays. With the beginning of the elevation of serum E2 level from 28 days of age, all parameters except body weight started to show drastic change until 31 days of age. The highest incidence of vaginal opening was recorded at 34 days of age. On macroscopic examinations, a number of rats showed uterine imbibition but vaginal opening. Immediately after the confirmation of the vaginal opening, the genital systems of three rats were observed microscopically. Both ovaries already had multiple corpora lutea, and degeneration of endometrial epithelial cells was observed. In conclusion, we obtained essential data on genital tract development of female Crj:CD[○!R] (SD) IGS rats for in vivo screening assays that will contribute to detect potential endocrine active chemicals. In addition, it is assumed that the first ovulation precedes or occurs simultaneously with vaginal opening. 幼若雌Crj:CD(SD)IGSラット(21-36日齢)について一般状態観察,体重を測定し,膣開口日齢を検査した.動物は各日齢で解剖し,解剖日に子宮,卵巣重量測定及び血清中の17β-estradiol(E2),progesterone測定を行った.28日齢以降みられたE2濃度の上昇に始まり,体重を除く全ての検査項目が31日齢までに明らかな変化を示した.膣開口は34日齢に最も高頻度にみられた.剖検所見においては,膣開口がみられていないラットの多くで子宮のimbibitionが観察された.解剖時に膣開口が観察されたラットの子宮,卵巣を病理組織学的に検査したところ,卵巣にはすでに黄体形成が確認され,子宮の所見は発情後期の像を呈していた.以上の結果,雌Crj:CD[○!R](SD)IGSラットの内分泌撹乱化学物質in vivoスクリーニング試験のための生殖器の発達に関する貴重なデータが得られ,また初回排卵は,膣開口の直前又は膣開口と同時に起こると推察された.