Effects of a non-steroidal pure antioestrogen, ZM 189,154, on oestrogen target organs of the rat including bones

ZM 189,154 ([1RS,2RS]-2-(4-hydroxyphenyl)-2-methyl- 1-[9-(4,4,5,5,5-penta-fluoropentyl)sulphinylnonyl]-1,2,3,4- tetrahydronaphth-6-ol) is a non-steroidal pure antioestrogen. It has a high relative affinity for the oestrogen receptor, completely blocks the trophic action of oestradiol (OE2) on the uterus in immature and ovariectomized (OVX) adult rats and, in the latter, also completely blocks the trophic action of OE2 on vagina, bone and growth rate. ZM 189,154 displays no intrinsic oestrogen-agonist activity on uterus, vagina, bone, LH secretion or growth rate in OVX rats. Differential sensitivity of OE2-regulated processes was more apparent in intact rats. Daily doses of 0.6 mg/kg per day of ZM 189,154 blocked ovulation; 2 mg/kg per day achieved maximal uterine atrophy but did not affect bone density or growth rate; 10 mg/kg per day produced a broader spectrum of effects (reduced bone density, increased basal LH, slightly increased growth rate), but the magnitude of these was smaller than after ovariectomy; the 10 mg/kg dose also produced multiple ovarian follicular cysts. The failure of ZM 189,154 to achieve complete ovariectomy-like effects in intact rats may be due to the action of ovarian factors other than OE2, or to the circulating OE2 levels resulting from the disturbance to ovarian function posing too strong a challenge to the antagonist.