IN VITROCONTRACTURE OF PSEUDOPREGNANT UTERINE MUSCLE CONTRASTED WITH ESTROUS MOTILITY

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Abstract
Using excised uterine strips in vitro, it is shown that uterine muscle of the sow in the lutein phase of the cycle and of the rabbit in pseudo-pregnancy respond to electrical stimulation in all respects similarly to that of the same sp. in estrus. The uterine muscle of both spp., when under the dominance of progesterone, spontaneously develops a state of contracture and, contrary to previous reports, is not relaxed or inhibited. This contracture is reversible and can be suspended by electrical shock or anoxia. The O2 tension in the bath and the temp. have a direct relationship to the speed of development of the contracture. Using frequent electrical stimulation (6-15/min.) the progesterone contracture can be imitated with strips from estrous uteri. Incomplete contracture has been observed on the 2d day of pseudopregnancy, representing an intermediate stage between estrus and the full development of pseudopregnancy. Response to epinephrine cannot be observed distinctly if contracture is fully developed. Pitocin has a definite effect on pseudopregnant uterine muscle, producing a suspension of the progesterone contracture. This action is the reverse of that exerted upon estrous muscle.

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