Affiliation:
1. Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland
Abstract
Ovariectomized white rats were treated as follows: group 1, 6.0 µg estradiol benzoate daily for 5 days; group 2, 6.0 µg estradiol for 3 days, then 1.6 µg estradiol plus 12 mg progesterone for 5 days; group 3, untreated controls. Membrane potentials were recorded from single uterine fibers, tension from the entire uterus. Untreated control fibers were quiescent, having a mean resting potential of 35.2 mv. Estrogen-dominated fibers were rhythmically contractile and had a mean resting potential of 57.6 mv. A train of action potentials accompanied and preceded each contraction of the muscle. In certain areas the fibers showed pacemaker-like characteristics, i.e. slow membrane depolarization between action potentials. Progesterone-dominated fibers had significantly higher resting potentials, mean 63.8 mv, but no localized pacemaker areas. Action potentials did not consistently precede or accompany contractions. In groups 1 and 2, acetylcholine stimulated contractions, lowered the membrane potential and increased the discharge rate of action potentials. Epinephrine diminished contractions, raised the membrane potential and abolished the action potential discharge.
Publisher
American Physiological Society
Cited by
143 articles.
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