Effect of low doses of continuously administered catecholoestrogens on peripheral and central target organs

Osmotic minipumps containing low doses of either 4-hydroxyoestradiol or 2-hydroxyoestradiol2) were sc implanted for 152 h (6 1/3 day) into immature male and female rats. At the end of the test period the animals were killed and the uterine weight, the vaginal opening, the gonadotrophin serum levels and the gonadal weight monitored. The following results were obtained: 1) a significant increase in the uterine weight and a consistent vaginal opening were observed after 4-hydroxyoestradiol but not after 2-hydroxyoestradiol treatment, 2) LH-levels increased after 2-hydroxyestradiol but not after 4-hydroxyoestradiol; the increase was, however, not significant, 3) FSH-levels and gonadal weights were lowered by 4-hydroxyoestradiol treatment in male animals only; 2-hydroxyoestradiol had not effect on FSH-levels in both sexes, 4) in no instance an antioestrogenic effect of either catecholoestrogen was observed. It is concluded that 4-hydroxyoestrogens - using the above paradigm - have a significant importance on uterine growth and vaginal opening but (on day 6) no role of LH-release, whereas 2-hydroxyoestrogens may increase LH levels (on day 6) but are nearly ineffective with respect to peripheral parameters.