Comparison of alpha- and beta-receptor stimulation in the circular and longitudinal muscle of the oestrogen and progesterone dominated rabbit uterus.

Abstract

Abstract: Longitudinal and circular muscle strips from the progesterone‐dominated rabbit uterus were stimulated in vitro with the α‐ and β‐adrenergic agents noradrenaline and isoprenaline, and the effects were compared with results obtained from the oestrogen‐dominated uterus. The spontaneous activity in oestrogen‐ and progesterone‐dominated strips was the same. Noradrenaline caused an increase in frequency and basal tone in all strips. In the oestrogen‐dominated strips the force of the induced contractions exceeded the force of the spontaneous contractions. In the progesterone‐dominated strips the force of the contractions subsequent to the addition of noradrenaline was usually a little reduced. No difference between the circular and longitudinal strips was observed. Reserpine‐treatment of the oestrogen‐dominated animals substantially reduced the force of the noradrenaline‐induced contractions. In progesterone‐dominated animals reserpine treatment had no such effect. Isoprenaline produced a reduction in the force and the frequency of the spontaneous contractions. In the circular strips, the spontaneous activity was less inhibited by isoprenaline in the progesterone than in the oestrogen‐dominated strips. As to the longitudinal strips, the dose‐response curves were quite similar. The circular strips were much less inhibited by isoprenaline than were the longitudinal ones. It is concluded that the different reactions to adrenergic nerve stimulation in oestrogen‐ and progesterone‐dominated rabbit uteri reported previously by other investigators, might depend on the different reactions of the muscle to α stimulation, this difference being partly explained by the higher catecholamine content of the oestrogen‐dominated tissue.