The development of the mouse ovary and its response to exogenous gonadotrophins

Immature mice aged 14 to 49 days were treated with a single injection of 4 i.u. HCG, or 3 i.u. PMSG followed 48 hr later by 2 i.u. HCG. After treatment with HCG alone the number of oocytes which were ovulated rose gradually from Day 21 to Day 28 and then remained constant, while the combined PMSG+HCG treatment induced a peak response between Days 24 and 28. The percentage of animals responding also varied with age and treatment. After the combined PMSG+HCG treatment, 90% of the animals ovulated on Day 21, while a similar proportion was not achieved in response to HCG alone until Day 32. The variation in response with age and treatment was related to follicular development within the ovary.