Abstract
The effects of chronic administration of estradiol and hexestrol on the plasma cholesterol level were studied in male rats weighing 200 to 250 gm. When 0.3 mg per rat of estradiol was injected subcutaneously twice per week, the plasma cholesterol level initially decreased for a week, but then turned to increase and finally attained to 2 to 2.5 times the initial level at the end of 3 weeks. When varing amounts of estradiol were given, the least amount (0.03 mg per rat) gave only a slight increase of the plasma cholesterol level which was gradually elevated during the hormone treatment. Conversely, the largest amount (0.3 mg per rat) of estradiol caused an initial decrease followed by a significant increase in the plasma cholesterol level. The moderate amount of estradiol produced an intermediate responses of both hypo-and hypercholesterolemic effects. When the dose of estradiol was gradually increased by injection, the hypocholesterolemic effect was observed more evidently. In contrast to the biphasic effect of estradiol, a single effect, hypocholesterolemic, was induced by hexestrol during the treatment. The hypocholesterolemic response to hexestrol was, however, gradually reduced after the successive injection and finally disappeared, but this tachyphylactic phenomenone was prevented by the gradual increase of the dosage for every injection. Testosterone propionate caused no effect on the manifestation of the hypocholesterolemic effect of estrogens but it suppressed the hypercholesterolemic effect of estradiol. From these results, the dual effect of estrogens on the rat plasma cholesterol level was discussed.
