抄録
The relationships among progesterone and oestradiol contents in the sera, membrane activities, catecholamine actions and contents of cyclic nucleotides were investigated in the rat myometrium during gesta-tion and post partum, and under conditions of hormone treatment. Progesterone contents declined and oestradiol contents increased in the sera on the 21st day of gestation. During the late stage of gestation, oestradiol related to a regularity, and progesterone to an irregularity, in the spike generation of myometrial cells. In the longitudinal muscle, catecholamines dominantly activated the β-adrenoceptors during gesta-tion, but activation of the α-adrenoceptors was seen during and after delivery, while in the circular muscle, α-adrenoceptor dominancy altered to β-adrenoceptor dominancy at the last stage of gestation. In both muscle cells, increases in the cyclic AMP contents and activations of the β-adrenoceptors by application of catecholamines appeared simultane-ously. At the late stage of gestation, oestradiol treatment rather than pro-gesterone increased the cyclic AMP contents, in both muscle layers. In the light of the results, alteration in the myometrial properties during the last stage of gestation and delivery cannot be explained solely by progesterone withdrawal phenomena.
