The effect of luteectomy-induced progesterone-withdrawal on the oxytocin and prostaglandin response of the first trimester pregnant human uterus

Abstract

In 9 normal first trimester pregnant patients strong stimulation with a single i.v. dose of 250 mU oxytocin, or 100 μg PG F2α, only provoked barely detectable and transient contractures, rather than advanced cyclic IUP. Evidently, the normal early pregnant human uterus is not an “inert” muscle organ, but is “refractory” to stimulants. Luteectomy-induced rapid and continued P-withdrawals in 5 of the 9 patients “converted” these “refractory” uteri to “responsive” organs. This “conversion” was revealed by advanced cyclic IUP during the OR and PGR within 24–48 hours after luteectomy. Abortion occurred in 60.6±7.6 hours. “Conversion” was delayed in those 2 patients whose P-withdrawal was slow and who only aborted after 140.5±13.5 hours. The remaining 2 patients, whose luteectomy induced P-withdrawal was moderate and transient showed no “conversion” and failed to abort. The rate and degree of P-withdrawal in these 3 groups of patients was a function of gestational age. Apparently the normal pregnant human uterus is a suppressed organ, refractory to stimulants. Continued P-withdrawal suspends suppression, lowers threshold and thus “converts” the refractory uterus to a reactive organ. Once “converted” the pregnant human uterus becomes spontaneously active under endogenous stimulation and expels its contents, a process which can be hastened by exogenous stimulants.