Cyclic adenosine 3'5'-monophosphate and the relaxant action of relaxin in the rat uterus in vivo.

The relationship between relaxant actions of relaxin in the uterus and changes in uterine cAMP concentrations was assessed in anaesthetized bilaterally ovariectomized nonpregnant rats. Relaxin i.v. bolus (5 μg kg -1 ) did not change cAMP concentrations but inhibited uterine contractions with rapid onset. Uterine contractions were significantly reduced by 30-70% for 60 min. Relaxin (50 μg kg -1 ) produced a short-lived (up to 5 min) and small (up to 3-2-fold) increase in cAMP concentrations plus a marked (90%) and prolonged inhibition of uterine contractions (70-90% over 60 min)