Failure of Hypophysectomy to Affect Regression of Cyclic Hamster Corpus Luteum

The oestrous cycle of the hamster differs from the mouse and rat in two unique features: the extreme regularity of the 4-day cycle and the fact that the corpora lutea always begin to show signs of histological regression by Day 3 and have almost completely vanished by the next ovulation. The rapidity of luteolysis raises the question whether luteal regression in the cyclic hamster is attributable to withdrawal of pituitary luteotrophic hormone(s) or to a surge in release of a hormone which directly destroys the corpus luteum. In the following experiment, these alternative possibilities were explored by hypophysectomizing hamsters on Day 1 of the cycle (metoestrus) and determining the subsequent fate of the corpora lutea in comparison with those in intact cyclic or pregnant animals. Serial sections of ovaries from three different hamsters were examined for each day; the ovaries were sectioned at 10 μ and stained with haematoxylin