MITOTIC ACTIVITY IN THE ANTERIOR HYPOPHYSIS OF FEMALE RATS OF DIFFERENT AGE GROUPS AND AT DIFFERENT PERIODS OF THE DAY11

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Abstract
In different age groups of sexually mature [female] rats the post-ovulatory mitotic activity in the hypophysis was greatest in rats 50-80 days of age and gradually declined in the older age groups. In those animals 300 days or older the number of mitoses reached a low level and was no greater than that in young animals in diestrus. It was concluded that the decline in mitotic figures with advancing age is due to some change in the cells of the hypophysis that makes them increasingly refractory to factors that cause mitosis. There were significantly fewer mitoses in the hypophysis during the 9-hr. period after midnight than at other periods of the day. The mitotic count was tripled in the hypophyses of animals receiving colchicine intraperitoneally 9 hrs. before death.