It has been shown that the ovarian hormones oestrogen and progesterone regulate the behaviour of the myometrium, and that the reactions of the uterine musculature are determined by the relative amounts of the two hormones secreted. These effects have been demonstrated both in vitro (Csapo & Corner, 1952; and in vivo (Schofield, 1954(Schofield, , 1955.Contractility is dependent basically on the intracellular concentration of actomyosin, ATP and other high-energy phosphates, and these substances are maintained by the presence of a minimal amount of oestrogen which is responsible for their synthesis (Csapo, 1950;Menkes & Csapo, 1952). It can be assumed that after puberty, in the rabbit, oestrogen levels are always adequate to maintain at least a basic level of intracellular contractile proteins in the myometrium, and the uterus is always capable of contracting if suitably excited. Superimposed on this basic level of oestrogen there may be a higher level of oestrogen secretion when the uterus can be said to be 'oestrogendominated', or alternatively a high level of progesterone when the uterus would be 'progesterone-dominated'. After puberty, therefore, the myometrium is dominated by either oestrogen or progesterone according to the relative amounts of these two hormones secreted. The uterus behaves differently when under the dominance of oestrogen and of progesterone respectively; although the intracellular contractile system maintained by minimal levels of oestrogen is apparently the same, the reactions of the myometrium to a given set of stimuli are different. Csapo (1954) has shown that this difference is due to the effect of progesterone on the myometrium in inhibiting in some way the link between the stimulus and the contractile proteins (activation) and the passage of the stimulus along the muscle to activate the contractile elements simultaneously (conduction). Further analysis indicates that these variations are due, not to any difference in cellular structure or in the 1 PHYSIO. CXXXVIII
Investigations concerning the physiology of uterine muscle have accumulated a mass of valuable data in a variety of animals. Many of the findings are, however, contradictory and in the evaluation of these data one of the pressing questions is, can the differences be accounted for purely on the basis of species difference? The fact that wide variations are reported in the same species indicates that other factors are also involved.It has been emphasized by Csapo (1954a) that for a more complete understanding of myometrial function it is necessary to break down the complexity of the myometrium and study it in steps at different levels of organization. This has been done in the last fifteen years on cross-striated muscle and much valuable information has been drawn from the observations (Szent-Gyorgyi, 1953). The study of uterine muscle is somewhat complicated by the regulating effect of the two ovarian steroids, oestrogen and progesterone, which determine its functional state. The influence of these hormones, therefore, has to be carefully controlled if any constancy in the results is to be obtained. Csapo (1950a, 1953a) has shown that uterine muscle can be closely compared with skeletal muscle at the molecular and cellular levels and that the same chain of events occurs during the contraction cycle in both types of muscle. Actomyosin is the intracellular contractile element deriving its energy from the high energy phosphate compounds adenosine triphosphate (ATP) and creatine phosphate. Moreover, the character of the isometric contraction which is developed by the myometrium on the application of electrical and pharmacological stimuli is closely related to the intracellular concentration of the monovalent cations. Csapo demonstrated by these observations that the uterus is built on a framework similar to that of skeletal muscle. Csapo & Corner (1952) have shown how this basic structure and function of the uterine muscle is * Present address: Royal Veterinary College, London, N.W. 1.
The comprehensive review by Gruber (1933) indicates how conflicting is the evidence concerning the influence of the hypogastric nerve on the uterus in different species, and, because of this diversity, data relating only to the rabbit are referred to and discussed in this paper. Langley & Anderson (1895) concluded that the sole nerve supply to the uterus of the rabbit is through the hypogastric nerve, and is excitor in effect. Dale (1906) and Cushny (1906) both found that hypogastric stimulation and adrenaline injection had similar excitor effects on the uterus and this has been confirmed by subsequent workers. Mann (1950) analysed blood obtained from the uterine veins and found that both adrenaline and noradrenaline were present in increased amounts during stimulation of the hypogastric nerve. She also found that the uterine response to hypogastric stimulation was not potentiated by eserine and was abolished by dibenamine. She concluded that the nerve fibres concerned are adrenergic.Evidence exists which suggests that the fibres are cholinergic rather than adrenergic. Labate (1941) was unable in the majority of experiments to potentiate the effects of adrenaline and hypogastric stimulation on the uterus with cocaine, and he therefore assumed that the majority of the hypogastric fibres in the rabbit are cholinergic. In later experiments Labate & Sheehan (1943) found that although small doses of atropine did not abolish the uterine responses to hypogastric stimulation, the response was abolished by large doses ranging from 10 to 50 mg. Langley & Anderson (1896) and Cushny (1906) noted that atropine in doses up to 50 mg did not affect the spontaneous uterine activity or the response of the uterus to hypogastric stimulation.The position of the ganglion cells of the hypogastric fibres is still a matter of some doubt. Langley & Anderson (1896) concluded that although some of the fibres supplying the uterus have a synapse in the inferior mesenteric ganglia, the majority of the ganglion cells lie close to the uterus. Cushny (1906) found that the excitor response of the uterus to stimulation of the hypogastric
Summary. A flock of thirty ewes was observed through two pregnancies to determine whether parturition could be delayed by the systemic administration of gestagens. In the first season, the four treated groups received daily injections of 2-5 and 10 mg, 6a-methyl-17a-hydroxyprogesterone acetate (6-map) and 10 and 40 mg progesterone for 14 days starting 1 week before the expected date of delivery. The time and course of delivery appeared to be unaffected. The following season the dose levels were increased to 25 and 40 mg 6-map, and 80 and 160 mg progesterone. A high proportion of pregnancies was affected by this treatment. Some sheep delivered to schedule but most of the others had to be subjected to Caesarian section. The mortality of lambs delivered at term was higher than in the control group and in all the cases of delayed parturition the lambs died in utero. The foetal death was not considered to be due to post-maturity. The results are discussed and it is concluded tentatively that placental progesterone in the ewe is not replaceable by systemic progesterone.
The development of a pressure-sensitive radio transmitter (endoradiosonde) which can be surgically implanted and which has several weeks transmission life has provided a tool for the long-term appraisal of intra-uterine pressure which does not entail any connexion of the uterine cavity with the exterior. This is a valuable advance and as the authors were anxious to make a study of the aetiology of Ring-womb the radiosonde seemed an obvious aid. Ring-womb is a disorder which occurs in parturient ewes: labour starts but no progress is made and the cervix never dilates sufficiently for the lambs to be delivered. The incidence has a seasonal variation but in some areas a fairly high proportion of the ewes presented to the veterinary surgeon in the lambing season may have this disorder: Caesarean section is usually necessary. It seems likely that this non-dilatation of the cervix is due primarily to disordered myometrial activity and that an investigation of this would be the best approach. However, information concerning normal myometrial activity in the ewe is lacking and it was thought appropriate initially to follow intra-uterine pressure changes by means of radio telemetry during the last three weeks of pregnancy in normal ewes. Accordingly a small flock of sheep was kept at Risdon's Fishleigh, Hatherleigh, Devon and the following paper describes the results from ten successful experiments. METHODS TechnicalThe miniature radio transmitter shown in Fig. la was specially developed to allow longterm (up to three months) transmission of pressure information from the uterus. It differs from previously described radio pills (Wolff, 1961) in the following major respects.The method of encap&ulation. Almost all plastics and some potting materials exhibit both water absorption and transmission of water vapour. In addition some of the more easily machined and glued plastics such as Perspex and polystyrene tend to craze when used in thin sections. These effects are unimportant in gastro-intestinal application where a life of only
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