Alterations in the properties of the rat myometrium during gestation and post partum.

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Abstract
The relationships among progesterone and estradiol contents in the sera, membrane activities, catecholamine actions and contents of cyclic nucleotides were investigated in the rat myometrium during gestation and postpartum and under conditions of hormone treatment. Progesterone contents declined and estradiol contents increased in the sera on the 21st day of gestation. During the late stage of gestation, estradiol related to a regularity and progesterone to an irregularity in the spike generation of myometrial cells. In the longitudinal muscle, catecholamines dominantly activated the .beta.-adrenoceptors during gestation, but activation of the .alpha.-adrenoceptors was seen during and after delivery, while in the circular muscle, .alpha.-adrenoceptor dominancy altered to .beta.-adrenoceptor dominancy at the last stage of gestation. In both muscle cells, increases in the cAMP contents and activations of the .beta.-adrenoceptors by application of catecholamines appeared simultaneously. At the late stage of gestation, estradiol treatment rather than progesterone increased the cAMP contents, in both muscle layers. In 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.

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