Comparison of beta 1- and beta 2-receptor stimulation in oestrogen or progesterone dominated rat uterus

Electrical stimulation of rat uterine preparations induced constant and reproducible contractions. The inhibitory effect of some adrenergic substances was tested on oestrogen- or progesterone-primed electrically stimulated rat uteri. The rank order of the relative potencies of some adrenergic agonists was shifted from Iso greater than E greater than Salb greater than Ne greater than H 133/22 greater than Phe greater than Clo in the oestrogen primed uterus to Iso greater than Salb greater than E greater than Ne greater than Phe greater than Clo greater than H 133/22 in progesterone primed uterus. The selective beta 2- agonist salbutamol was relatively more potent in progesterone treated rats than in oestrogen treated, while the beta 1-agonist H 133/22 was more potent in oestrogen dominated uterus. We therefore suggested that beta 2-receptors is dominating in the progesterone primed uterus, while both beta 1 and beta 2-receptors could be found in oestrogen primed uterus. No dissociation between the inhibitory effect on contractility and the cAMP increasing effect of isoprenaline could be demonstrated in rat uteri.