EFFECTS OF SEX STEROIDS ON THE CHOLINE ACETYLASE ACTIVITY IN THE HYPOTHALAMUS OF FEMALE RATS

Abstract

The effects of gonadal hormones-estradiol, progesterone and testosterone on the activity of choline acetylase in relation to the synthesis of acetylcholine in the hypothalamus of the spayed rats were studied to clarify the feedback mechanism of those gonadal steroids on the central nervous system. The following results were obtained: The elevation in the choline acetylase activity in the hypothalamus following ovariectomy was reduced to the level of the normal control by daily injection of estradiol benzoate in a range of doses of 0.1μg to 10μg. Attention should be given to the finding that the posterior hypothalamus is mainly responsible for the inhibitory effect of estradiol. However, no definite effect of estradiol was observed in the rats on the 20th day and the 100th day after castration which showed the lowered enzyme activity in the hypothalamus. Progesterone or testosterone had no demonstrable effect on the choline acetylase activity in the hypothalamus except that as small as 10μg of testosterone caused an increase in the activity of the rat on the 20th day after castration. It seems reasonable to conclude from the results mentioned above and those from the studies on cholinesterase and acetylcholine in this laboratory that there is the estrogen sensitive structure of cholinergic nature in the hypothalamus, especially in its posterior part, and the structure is closely involved in the mechanism of the secretion of gonadotropins as well as in the feedback mechanism of the steroid.