Chronic treatment of female rhesus monkeys with low doses of the antiprogestin ZK 137 316: establishment of a regimen that permits normal menstrual cyclicity

Large doses of antiprogestin typically disrupt menstrual cyclicity, A chronic low-dose regimen of the potent new antiprogestin ZK 137 316, which permits continued menstrual cyclicity but alters gonadal-reproductive tract activity, was established, Rhesus monkeys received vehicle (n = 6) or 0.01 (n = 8), 0.03 (n = 8) or 0.1 (n = 5) mg ZK 137 316/kg body weight daily for five menstrual cycles (C-1 to C-5), Oestradiol, progesterone and gonadotrophin profiles were normal during cycles involving vehicle and 0.01 and 0.03 mg ZK 137 316/kg body weight, In the 0.1 mg/kg group, mid-cycle oestradiol and gonadotrophin surges, and subsequent progesterone production, were absent in C-3 and C-5, Ovarian cyclicity was accompanied by timely menstruation in the vehicle and 0.01 mg/kg groups, By C-3, half the animals in the 0.03 mg/kg group and all animals in the 0.1 mg/kg group were amenorrhoeic, A corpus luteum was noted during the mid-luteal phase of C-5 in the vehicle, 0.01 mg/kg and 0.03 mg/kg groups, Large antral and cystic follicles were evident in the 0.1 mg/kg group, Thus, a daily treatment with 0.01 mg/kg ZK 136 317 permitted normal menstrual cyclicity in macaques, While the daily administration of 0.03 mg/kg ZK 136 317 allowed ovarian cyclicity, menstruation was disrupted in some animals, Increasing the dose to 0.1 mg/kg antagonized pituitary function and resulted in anovulation and amenorrhoea, A chronic low-dose regimen of the antiprogestin ZK 137 316, which permits normal ovarian/menstrual cyclicity, has potential as a contraceptive in women.