[New data on the "critical period" of the luteinizing action of estradiol benzoate in female rats].

The luteinizing action of oestradiol benzoate (OB) has been studied in 4-day cyclic female Wistar rats submitted to a dose of 10 mug on the morning of dioestrus I at 10-11 a.m. In a first experimental series a blockage of luteinization was observed in females injected with pentobarbital (PB) either on dioestrus I at 11 a.m. and 5 p.m. respectively or on dioestrus II at 1:30 p.m. In the second series the blockage of luteinization only occured in females injected with PB on dioestrus II at 1:30 p.m. Early mating during the night following dioestrus II overcame this action of PB. The luteinizing effects of OB were therefore concluded to be dependent on the activation on the afternoon of dioestrus II, of the nervous hypothalamic structures. They were also shown to depend on the sensitivity to PB and/or to OB, on the day of dioestrus I, of the hypothalamo-pituitary system.