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STUDIES ON THE MECHANISM OF NIDATION

Summary.: A single administration of ergocornine methanesulphonate (ECO) interrupts pregnancy of the rat when given on any day until the 7th after coitus, but not later. The drug also interrupts pseudopregnancy at any time during its course, without temporal limitation. The failure of ECO to interfere with pregnancy is correlated with the presence and endocrine activity of an implanted conceptus.

The factors causing failure of ECO to interfere with gestation after implantation were identified by a series of successive steps : (1) The presence of deciduomata—thought to be analogous to maternal decidual tissue—in the pseudopregnant uterus was shown not to oppose ECO action. (2) Animals, whose foetuses have been removed, leaving only maternal and foetal placenta in situ, were protected against the action of ECO. Thus, this implicated by elimination the foetal placenta as causing failure of ECO action in pregnancy after the 7th day. Indeed, placental grafts from late pregnant donors could be shown to overcome ECO action even in this first 7-day period.

As early as the 10th day, a luteotrophic influence was present in placental extracts, as measured by prevention of ECO action on pregnancy. In the literature, a luteotrophic influence is attributed to (foetal) placental tissue. The failure of ECO to interrupt pregnancy by the 8th day is taken as indication of placental luteotrophic activity at that time, i.e. 3 days before it can be detected when hypophysectomized rats are used for this purpose.

The action of ECO is considered as mediated by pituitary LtH depression. Thus, the use of this drug allows suppression of LtH without performing hypophysectomy. Placental luteotrophin is not affected by ECO.