Desensitization of rabbit myometrium to oxytocin and prostaglandin F2 alpha

The desensitizing effects of oxytocin (OT) and prostaglandin F2 alpha (PGF2 alpha) were investigated in the uteri of rabbits. Uterine motility was measured in anesthetized rabbits infused intravenously with either PGF2 alpha (50 micrograms/min) or OT (100 mU/min) alternately. The treatment sequence was saline (30 min), first drug (OT or PGF2 alpha, 90 min), second drug (OT if PGF2 alpha was first drug and vice versa, 90 min), and first drug (repeated) 60 min. Both OT and PGF2 alpha infusions increased motility approximately 200% within 5-10 min. Thereafter, motility decreased linearly to base-line value. Fifty percent desensitization was completed at 35-45 min and 100% at 90 min. A tenfold increase in the infusion rate caused no further increase in motility. However, OT infusion into a PGF2 alpha desensitized uterus (and vice versa) elicited an immediate uterokinetic response. Oxygen consumption and glucose oxidation rate of uterine slices measured at different stages (preinfusion, maximal motility, and desensitized) of uterine motility showed no difference (P greater than 0.05) between the two experimental treatments. It was concluded that either OT or PGF2 alpha infusions specifically desensitized the uterus.