Journal of Clinical Endocrinology & Metabolism, Vol 51, 1311-1315, Copyright © 1980 by Endocrine Society

ARTICLES

Synergism of estrogen and bromergocryptine in the induction of luteolysis in cynomolgus monkeys (Macaca fascicularis)

VD Castracane and AA Shaikh

Sequential administration of estrogen (40 microgram depoestradiol cypionate and estradiol benzoate) on cycle days 18--20 and bromergocryptine (CB-154; 0.5 mg/kg, twice daily) on cycle days 20-22 induced luteolysis in seven of nine cynomolgus monkeys, significantly shortened menstrual cycles (23.5 +/- 0.7 days), and caused a significant decline in plasma progesterone levels during the period of CB-154 administration. Two treated monkeys did not have shortened menstrual cycles, although a luteolytic effect on plasma progesterone was evident. One monkey with a late ovulation (confirmed by endocrine parameters and laparoscopic observation) was treated with the same regimen in the early luteal phase; this also resulted in a decline in plasma progesterone and a shortened luteal phase (11 days). Treatment with the estrogen or the CB-154 component alone had no effect on menstrual cycle length or plasma progesterone levels. Similarly, treatment with CB-154 throughout the luteal phase had no effect on luteal function. An abbreviated treatment consisting of 1 day of estrogen and 1 day of CB-154 administration gave some indication of a luteolytic effect. None of these treatments produced detectable side effects. These studies have demonstrated a synergism of estrogen and CB- 154 in the induction of luteolysis in cynomolgus monkeys. The present regimen, because of the effectiveness and apparent lack of side effects, deserves further investigation for possible clinical application.