Neural timing of ovulation in immature rats treated with gonadotrophin.

Treated with Gonadotrophin Thirty-two-day-old female rats, injected two days previously with gonadotrophin from pregnant mares' serum, were given barbiturate at different times during the afternoon to determine whether the ovulation that would occur the next day could be blocked. The results indicate that ovulation depends upon release of pituitary ovulating hormone during a"critical period" between 2 and 4 P.M.