THE ACCUMULATION, RETENTION AND INTERACTION OF OESTRADIOL AND OESTRONE IN CENTRAL NEURAL AND PERIPHERAL TISSUES OF GONADECTOMIZED FEMALE RATS

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Abstract
SUMMARY: Adult female rats which had been ovariectomized and hysterectomized were given tritiated oestradiol or tritiated oestrone and killed 1, 2 or 4 h later. Several brain samples were taken including anterior hypothalamus, posterior hypothalamus, 'cerebral peduncle' and cerebral cortex. Pituitary and blood plasma samples were also taken. [3H]Oestradiol and [3H]oestrone showed different patterns of retention in basal brain structures. After [3H]oestradiol administration the anterior hypothalamus retained more radioactivity than the posterior hypothalamus, which in turn retained more radioactivity than the cerebral peduncle. With [3H]oestrone, samples from the cerebral peduncle and posterior hypothalamus retained more radioactivity than samples from the anterior hypothalamus. The cerebral peduncle and posterior hypothalamus did not differ from one another in this respect. After administration of either hormone, all basal brain structures retained more radioactivity than cerebral cortex and plasma. The pituitary retained six times more radioactivity after administration of [3H]oestradiol than after [3H]oestrone. For ovariectomized females killed 2 h after the injection of [3H]oestradiol, pretreatment with oestradiol for 30 min reduced the radioactivity retained in the pituitary and anterior hypothalamus, while pretreatment with oestradiol for 24 h produced no changes in uptake except in the uterus where radioactivity levels were nearly doubled. The increased uterine uptake was independent of increases in uterine weight. Oestrone pretreatment failed to produce consistent effects except at high doses where it reduced [3H]oestradiol uptake in the pituitary and hypothalamus. Pretreatment with either oestrone or oestradiol had no effect on uptake by neural tissues after [3H]oestrone injection. It is concluded that there are at least four kinds of oestrogen uptake mechanisms in the female rat. The uterus contains a limited capacity 'receptor system' which selectively accumulates oestradiol and which permits displacement of oestradiol by oestrogen post-treatment, and stimulation of oestradiol uptake by oestrogen pretreatment. In the pituitary, oestradiol is selectively accumulated by a limited capacity receptor system which permits oestradiol displacement, but not oestradiol uptake stimulation. The brain contains two receptor systems: a regionally localized limited capacity receptor system for the non-displaceable selective accumulation of oestradiol, and a regionally localized comparatively unlimited capacity receptor system for the selective accumulation of oestrone.

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