PRETREATMENT WITH PORCINE RELAXIN AND MG IONS ENHANCES INHIBITORY EFFECTS OF DIBUTYRYL-CYCLIC-AMP IN LONGITUDINAL MUSCLE OF ESTROGEN-TREATED RAT MYOMETRIUM

Phasic contractions were evoked in Mg-free Krebs solution by electrical stimulation in the longitudinal myometrial strip taken from estrogen-treated rats, and the application of 30 mu M dibutyryl cyclic AMP (db cAMP) for 15 min depressed the amplitude of contraction to 81+/-18% (+/-SD, n=23) of the control. The contractile depression caused by db cAMP was not significantly altered by pretreatment with either 1 mM Mg (40 min) or 100 mu porcine relaxin (15 min) alone; however it was markedly enhanced to 22+/-30% (n=7) of the control response by the combined pretreatment with Mg and relaxin. The enhancement lasted for longer than 2 h thereafter in Mg-free Krebs solution. It was discussed that some memory factor was induced by relaxin in the presence of 1 mM Mg to respond strongly to db cAMP.