BIOSYNTHESIS OF OVARIAN STEROIDS IN RABBIT - INFLUENCE OF PROGESTERONE OR ESTRADIOL IMPLANTATION INTO HYPOTHALAMUS AND LIMBIC STRUCTURES

The feedback action of progesterone and estradiol was investigated directly in rabbits by implanting a small amount of solid progesterone or estradiol in the hippocampus, amygdala, and hypothalamus, and estimating its influence on the incorporation of acctate-1-C14 into ovarian steroids by ovarian homogenate. The results were as follows: 1. Cl4-progestin formation from acetate-1 -C14 was markedly increased by progesterone implants in the alveus of the hippocampus. Therefore, this region might take part in a positive feedback mechanism that regulates progestin formation. 2. Estradiol implantation in the fascia dentata of the hippocampus resulted in a slight increase in C14-cstrogen (estradiol + estrone), 20α-hydroxy-pregn-4-en-3-one, and 17-hydroxyprogestcronc formation. 3. Progesterone implants in various parts of the amygdala caused little change in the biosynthesis of ovarian steroids. 4. Estradiol implants in the medial nucleus of the amygdala markedly suppressed C14-cstrogen formation. Therefore, this site seems to be related to the negative feedback control of estrogen formation. 5. Estradiol implants in various parts of the amygdala produced a decrease in the rate of progestin labelling.6. Progesterone implants in the supraoptic nucleus and anterior hypothalamic area did not greatly affect ovarian steroid biosynthesis, implants in the medial preoptic area suppressed Cl4-estrogen formation, and implants in the ventromedial hypothalamic nucleus and periventricular arcuate nucleus facilitated C14-esttogen formation. C,4-progestin formation was inhibited by progesterone implants in the ventromedial hypothalamic nucleus, but facilitated by implants in the periventricular arcuate nucleus. These results may suggest that the periventricular arcuate nucleus and ventromedial hypothalamic nucleus arc related to different feedback mechanism for progestin and estrogen formation and that the medial preoptic area is related to the reciprocal feedbak control of estrogen formation. 7. Estrogen formation was inhibited by estradiol implants in the medial preoptic area, anterior hypothalamic area, ventromedial hypothalamic nucleus and periventricular arcuate nucleus, but facilitated by implants in the supraoptic nucleus. Progestin formation was facilitated by estradiol implants in the medial preoptic area, anterior hypothalamic area, and ventromedial hypothalamic nucleus, and was inhibited by implants in the supraoptic nucleus and periventricular arcuate nucleus. © 1969 S. Karger AG, Basel.