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KMID : 0377619670120010057
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Korean Jungang Medical Journal
1967 Volume.12 No. 1 p.57 ~ p.68
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Experimental Study of the Action of Oxytocin on the Isolated Uterine Segment of Rabbits
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Abstract
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The first report of an extract of the posterior pituitary gland having an effect on the uterus was described in an article on “The physiological action of ergot” by Dale (1906). Bell (1909) soon utilized the extract in his practice and reported that it effectively reduced postpartum uterine hemorrhage. In 1911, Hofbauer introduced its use to stimulate uterine contraction during labor. Kamm et al. (1928) fractionated posterior pituitary extract into two polypeptide portions: one predominantly oxytocic (oxytocin) and the other predominantly vasopressor and antidiuretic in action (pitressin) and Du Vigneaud (1951) successfully synthetized these two polypeptides and described their structural formulas.
Although numerous investigators have shown the uterine contracting activity of oxytocin, the exact effects of this substance on the uterus are uncertain and many features are controversial. This uncertainty arises from species differences in response to oxytocin, the variable effects of the sex hormones on the responsiveness of the uterus and unknown factors influencing uterine activity. Knaus (1926) found that estrogen increases spontaneous motility and the response of the human uterus to pituitary extract. In reviewing the literature extensively, Henry and Brown (1943) concluded that the spontaneous activity of the human uterus and its sensitivity to pituitary extract are great in the luteal phase of the cycle and by the same token that progesterone is not a uterine sedative. However, the consensus among clinicians, contrary to the finding of Henry and Brown, is that progesterone reduces uterine motility and sensitivity to the posterior pituitary extract.
It is generally known that the responsiveness of the uterus to oxytocin varies during pregnancy and gradually increases to become maximal at term and immediately postpartum. The nonpregnant uterus is known to be much less responsive to this drug. However, no experimental data has been reported to indicate that oxytocin produces uterine relaxation. While examining the relationship between the uterine motility and myometrial catecholamines it was found that oxytocin significantly inhibited the motilty of the isolated uterine segment from progesterone-treated rabbits. This interesting finding led us to reinvestigate the mechanSism of the action of Oxytocin on the rabbit uterus, segment from oophorectomized estrogen-treated rabbits by directly acting on myometrium. However, there exists some possibility to suggest that an adrenergic mechanism may be partly involved in this stimulatory effect of oxytocin.
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