A comparison of progesterone and epinephrine inhibition on the myometrium of the rat

Abstract

This study was executed to gain insight into the possibility of a relationship between the smooth muscle depressing effects of epinephrine and of progesterone. The first part of the investigation considered the possibility that an adrenergic blocking agent, dichloroisoproterenol, may affect the ability of progesterone to exert its inhibitory effects on smooth muscle as the blocking agent does with epinephrine. The second was a comparative study on the oxygen-stimulating effects of epinephrine and progesterone. The rationale behind this last experiment was derived from observations of Bueding and Bulbring ∗ ∗ E. Bueding and E. Bulbring, in Pharmacology of Smooth Muscle, pp. 37–54, Macmillan, New York (1964). which have led them to the conclusion that the epinephrineinduced relaxation of smooth muscle is mediated through an increase in oxidative metabolism. Epinephrine (1.04 mg/ml) caused inhibition of the spontaneous contractions of rat uterine strips when bathed in Krebs original Ringer phosphate buffered solution. Progesterone, at a concentration of 20 mg/ml, also caused inhibition of spontaneous activity of the rat uterus under the same conditions. Dichloroisoproterenol, at 1 mg/ml, inhibited the depressing effect of epinephrine at the previously mentioned dose, but had no effect on the depressing effect of progesterone. Epinephrine caused an increase in the rate of oxygen consumption of the rat uterus at 5, 15, and sometimes 30 min, after which the rate diminished as the effect wore off. Progesterone caused a significant depression of oxygen consumption of the uterus over the entire hour measured, and especially during the last 15-min period. The conclusion was drawn from these results that epinephrine and progesterone depress smooth muscle activity via independent mechanisms.