ROLE OF CYCLIC ADENOSINE 3‘,5’‐MONOPHOSPHATE IN THE ISOPRENALINE‐INDUCED RELAXATION OF THE OESTROGEN DOMINATED RABBIT UTERUS

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Abstract
1 The role of cyclic adenosine 3′,5′-monophosphate (cyclic AMP) in the relaxation produced by isoprenaline in muscle strips from the oestrogen dominated rabbit uterus has been investigated. 2 Isoprenaline 2 × 10−8 M produced an inhibition of the mechanical activity but no increase in cyclic AMP. Isoprenaline 2 × 10−6 M produced both inhibition of mechanical activity and increase in cyclic AMP. 3 The increase in cyclic AMP, but not the inhibition of mechanical activity, was blocked by propranolol 3.4 × 10−6 M. 4 Dibutyryl-cyclic AMP produced a relaxation which mimicked that produced by isoprenaline, in that the longitudinal strips were more sensitive than the circular ones. 5 It is concluded that cyclic AMP may be a mediator of the β-adrenergic effect in the oestrogen dominated rabbit myometrium. However, it seems not to be an obligatory link between stimulation of β-adrenoceptors and relaxation. Other mechanisms may also exist.