Effects of metabolic inhibitors on the rat uterus and on its response to oxytocin

¹ Department of Pharmacology, Harvard Medical School, Boston, Massachusetts

Myometrial strips from white rats between the 6th and 9th and the 20th and 22nd days of pregnancy were arranged for the simultaneous recording of membrane potentials from single muscle fibers and isometric tension from the entire strip. The 6- to 9-day uteri behaved as though they were progesterone controlled, while the 20- to 22-day muscles seemed to be under the control of estrogen. Dinitrophenol (DNP) (10^–3 m) depolarized the muscle cell membrane and stopped all contractions in the 6- to 9-day uteri, but only diminished the contractions in the 30- to 22-day muscles. In both groups of muscles, DNP (10^–3 m) abolished the stimulatory action of oxytocin. The inhibitory action of DNP was reversible. Monoiodoacetic acid (IAA) (2 x 10^–4 m) abolished all activity and the response to oxytocin in both groups of muscles but, in contrast to DNP, there was no change in the level of the resting membrane potential. The action of IAA was irreversible.

Key Words: DNP depolarization of myometrial cell membrane • DNP and myometrial muscle contraction • IAA inhibition of myometrial muscle activity • estrogen- and progesterone-controlled myometrium • metabolic inhibition of rat myometrium • effects of oxytocin on metabolically inhibited rat uterus • effects of DNP and IAA on membrane potentials and contractions of the myometrium • effects of oxytocin on excitability and contractility of uterus during metabolic inhibition • effects of DNP and IAA on isolated rat uterus and its response to oxytocin

Submitted on June 26, 1963

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