AJP - Endocrinology and Metabolism, Vol 257, Issue 1 E20-E26, Copyright © 1989 by American Physiological Society
Desensitization of rabbit myometrium to oxytocin and prostaglandin F2 alpha
H. Eiler, C. S. Armstrong-Backus and W. A. Lyke
Agricultural Experiment Station, University of Tennessee, Knoxville 37901.
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.
