Luteolysis and termination of early pregnancy in the rhesus monkey with prostalene, a synthetic prostaglandin analog

Prostalene, a synthetic prostaglandin (PG) analog was compared to PGF 2α for ability to both shorten the luteal phase and to terminate early, confirmed,pregnancy in the rhesus macaque. 15mg of either prostalene or PGF2a administered as a single intramuscular injection 30 days from last menstrual bleed aborted all treated animals. In contrast, while a single dose of 15mg of prostalene administered 7 days before expected menstruation to regularly cycling, non-pregnant monkeys shortened the luteal phase by 5.0 ± 0.7 days, the same dose regimen of PGF2a was ineffective whether judged by circulating levels of progesterone or by menstrual cycle length. Mean, peripheral, plasma progesterone levels in the non-pregnant monkeys declined abruptly following prostalene treatment. Although menstrual flow was of normal duration, the cycle length following the prostalene treated cycle was greater than pretreatment cycle lengths, suggesting that follicular maturation was not accelerated after treatment. Experiments in the mare and pregnant hamster demonstrated that a two fold increase in dose above the luteolytic dose of prostalene was required to ensure immediate return of ovulation. It is suggested that prostalene demonstrates both luteolytic and hypothalamo-pituitary stimulating properties but at different dose levels. The compound may thus be useful in dissecting the differing biological mechanisms concerned.