Role of cyclic adenosine 3',5'-monophosphate in the isoprenaline-induced relaxation of the oestrogen dominated rabbit uterus.

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 times 10- minus 8 M produced an inhibition of the mechanical activity but no increase in cyclic AMP. Isoprenaline 2 times 10- minus 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 X 10-MINUS 6 M. 4. Dibutyryl-ccylic 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 beta-adrenergic effect in the oestrogen dominated rabbit myometrium. However, it seems not to be an obligatory link between stimulation of beta-adrenoceptors and relaxation. Other mechanisms may also exist.