Aromatization in the Central Nervous System of Rabbits: Effects of Castration and Hormone Treatment 1

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Abstract
In vitro incubation of tissue homogenates from the hypothalamus and limbic system of adult male and female rabbits with A4 androstene- 3-17-dione-7-3H resulted in the formation of tritium-labeled estrone. There was no measurable conversion by the pituitary gland, olfactory lobes and cerebral cortex. Activity was primarily localized in the anterior hypothalamus. While in female rabbits the amount of limbic activity was equal to that in the hypothalamus, in males the hypothalamus was more active than the limbic system. Addition of large amounts of nonradioactive estrone to the incubation had no dramatic or consistent effect on aromatization. There was a significant sex difference in hypothalamic activity; the male being three times as active as the female (p > 0.02). The aromatizing activity in male limbic system was consistently higher than in the female. The sex difference in the hypothalamus was diminished by chronic castration as a result of a markedly increased activity in both sexes. The limbic system of males and females also showed increased activity after castration. Estradiol treatment of the animals did not abolish the sex difference despite an increase in the activity of both hypothalamus and limbic system. Testosterone treatment diminished the sex differences. The male hypothalamus showed no effect of testosterone treatment while the activity in the female was stimulated to the level of the male. After testosterone administration, limbic aromatization increased in both sexes, resulting in a decreased sexual difference. Progesterone treatment caused significant decreases in the activity of male hypothalami while no effect was seen in females. As a result the sex difference was abolished. After progesterone the limbic system of both sexes showed inconsistent activity. These experiments indicate that aromatization in the central nervous system is influenced by the hormonal state of the animal.(Endocrinology92: 589, 1973)