Activity and drug responses of the sheep uterus in relation to reproductive condition

Abstract

It is well known that the activity, and response to drugs, of uterine muscle may alter with the reproductive condition of the animal. In a number of species there is, for instance, the phenomenon of reversal of the action of adrenaline, which, whilst it relaxes the non-pregnant uterus, in pregnancy causes contraction. It is not always clear from the literature whether the ovaries of the nonpregnant animals investigated contained corpora lutea. Certainly pregnancy is not always normally necessary for such a reversal; in the cow Cupps & Asdell (1944) found this reversal within the oestrous cycle.On the sheep uterus little work seems to have been done. Polovceva (1940) has made in vivo recordings from non-pregnant animals and found the strength of contractions greatly increased at the time of heat, and their frequency diminished. Recently Gunn (1944) has observed, in vitro, that adrenaline is motox to the non-pregnant uterus of the sheep but inhibitory at the time of parturition-a reversal in the opposite sense to those previously known.The results presented here coh2ern the spontaneous activity in vitro, and the responses to acetylcholine, adrenaline and posterior pituitary extract, of uteri from a number of ewes killed at various stages of pregnancy, and also from a few non-pregnant animals-some normal, other § previously treated with pregnant mare serum gonadotrophin or stilboestrol. It ias been found that the action of oxytocin is prolonged during pregnancy in that it is followed (a) by the appearance of characteristic 'slow' rhythmic contractions which may persist for as long as 1 hr. after the drug is washed out and which resemble the type of activity exhibited by strips of parturient uteri, and (E) by the potentiation of subsequent doses of acetylcholine. It is also shown that the action of adrenaline in pregnancy is a mixture of motor and inhibitory effects and that the inhibitory after-effects may depress the response to other motor drugs.

Relationship of Endocrine State to Spontaneous Motility of Sheep Myometrium

“…Earlier studies have suggested that spontaneous motility of the sheep uterus is greatest during estrus, diminishing with the development of a corpus luteum (Polovceva, 1942;Ambache and Hammond, 1949). In addition to confirming these published observations, the present results indicate that the uterus is moderately active without ovarian hormonal influences.…”

“…In sheep, neither the variation in spontaneous uterine motility during the estrous cycle nor the effects of exogenous ovarian hormones on this motility have been studied extensively. Most reports on the subject deal primarily with uterine activity in response to pharmacological agents, with ovarian status given secondary importance (Alexander, 1945;Ambache and Hammond, 1949), although Polovceva (1942) reported that uterine motility, studied in vivo, was greatest during estrus and lowest on the fourth or fifth day post estrus.…”

Spermatozoa in the Genital Tract of the Ewe I. Rapidity of Transport

“…They concluded that "excitement, fright, or other disturbing influences would affect motility in the uterus" and that "such action, in turn, would diruiuish or inhibit spermatozoan transport depending upon the degree of fright and the degree of stimulation resulting in the release of oxytocin" (Van Demark and Hays 1954). In ewes, oxytocin is released following vaginal distension (Debackere and Peeters 1960) and the uterine muscle responds to oxytocin by tetanic contractions (Alexander 1945;Ambache and Hammond 1949). While the response of the intact uterus of oestrous ewes to adrenaline has not been fully investigated, Alexander (1945) found that adrenaline inhibited uterine activity in both the pregnant and non-pregnant ewe.…”